Tomato Disease Investigation

 

A foliar disease on Tropic tomatoes in our hoophouse.
Pam Dawling

Tomato diseases are many, and are important because tomatoes are so popular! A couple of weeks ago, we started to notice yellowing of tomato leaves and upward/inward leaf-rolling in the middle of one of the two rows in our hoophouse, on the Tropic variety. The veins of the yellowing leaves remain green, a pattern called chlorosis. Yellowing indicates chlorophyll is not functioning, photosynthesis is not happening much and so no new leaves will grow, no sugars will be made and fruits will not be sweet and tasty.

One of our crew did some research and reported back that chlorosis can be caused by several physical problems, some nutrient deficiencies, or by disease, including a few viral diseases. The chlorosis is spreading to other varieties

The University of Illinois Urbana-Champaign Extension provides helpful starter info.

Seminis has a thorough 78-page 1997 well-organized downloadable pdf Tomato Disease Guide, with good photos.

Another source including good photos is the 168-page 2017 De Ruiter and Seminis Tomato Disease Field Guide available online from Bayer or Noresco. I’m not advocating using anything but organic methods, but these companies have good ID information.

Penn State has Scouting and Identifying Tomato Diseases, a short video, useful to learn how to scout well and what to look for.

Root-knot nematode (M. enterolobii) symptoms on ‘Rutgers’ tomato roots. Other species of root-knot nematode produce similar galling symptoms
T. Schwarz, NC State University

 Here’s our summary:

Chlorosis Cause 1: physical or chemical problems

  1. It could be a high pH problem. I think this is unlikely, but we can do a soil test in October.
  2. Injured roots? Check for root knot nematodes when we pull up the plants in a couple of weeks.
  3. Compacted roots? Very unlikely, unless someone has been stomping all round the stems.
  4. Poor drainage? Unlikely, unless
    Effects of excess soil salt levels on crop foliage.
    Photo Rose Ogutu, Horticulture Specialist, Delaware State University

    there were a big drip tape leak, which there has not been.

  5. Salt buildup? We have had very hot weather, maybe salts have built up faster than usual. We will soon do our twice annual salt washdown. This does seem possible.
  6. Clemson Extension provides info on leaf roll, see HGIC 2222, Tomato Leaves Rolling? “Excessive moisture and nitrogen, insufficient phosphorus, heat, drought, severe pruning, root damage from tilling or hoeing, early planting and transplant shock are some of the cultural and environmental factors that can cause physiological leaf roll in tomatoes. Initial symptoms are usually apparent in the lower leaves with an upward cupping of leaflets followed by an inward lengthwise rolling of the leaflets toward the mid-vein. The affected leaves tend to become thickened and have a leathery texture, but retain a normal, healthy green color. Over time, all of the leaves on the plant may be affected. . . The good news is that the condition has minimal impact on tomato fruit production and plant growth.” Viral infections and herbicide injury can also cause leaf roll (more on viral infections below).
Using a lawn sprinkler to wash down the salt build up in our hoophouse. Photo Pam Dawling

Chlorosis Cause 2: Nutrient deficiency

  1. Check which foliage turned chlorotic first. Younger tomato leaves are generally towards the top of the plant (or on sideshoots). Older leaves are lower. Mobile nutrients (nitrogen, phosphorus, potassium, magnesium, chlorine) show symptoms first on older leaves, and immobile nutrients (iron, manganese) show symptoms first on younger leaves.
  2. Of the immobile nutrients, iron chlorosis starts at the leaf base and the leaf becomes very pale; manganese deficiency looks like magnesium deficiency, but starts in the younger leaves, not the older ones as it does with magnesium deficiency.
  3. From the video Iron Deficiency in Tomatoes, from Matthew DeBacco, I really don’t think we have an iron deficiency. The younger leaves are not the main site of the problem, and our plants don’t have the elongated look that the ones in the video have.

    Chlorosis on our Tropic tomato leaves, plus mottled fruit.
    Pam Dawling
  4. From the nutrient deficiency photos on page 74 of the 1997 78-page downloadable pdf Seminis Tomato Disease Guide, ours look closest to the magnesium-deficient ones, IMO. Green veins with interveinal yellowing.
  5. The Illinois Extension says “Other elements such as calcium, zinc, manganese, phosphorus, or copper in high amounts in the soil can tie up iron so that it is unavailable to the plant. However, a shortage of potassium in the plant will reduce the availability of iron to the plant.” A soil test will show if we have shortages or excess of anything. Then we can add any needed amendments for the winter and next summer’s crops.
  6. Nutrient deficiencies would generally affect plants along the whole bed, but we have healthy Green Zebras right next to the Tropics.

    Healthy Green Zebra tomato plant right next to diseased Tropic.
    Pam Dawling
  7. Last winter’s crops in that bed were chard, senposai and turnips, all of which could have taken a lot out of the soil. But the bed was composted adequately on 10/9/23 with 5 barrows of compost for a 90’ x 4’ bed.
  8. Was there anything unusual about the planting of the tomatoes? Not enough compost in the holes? Not enough or too much firming of the soil around the tomatoes? Do we remember?

Chlorosis Cause 3: Tomato Chlorosis Virus ToCV or Tomato Infectious Chlorosis Virus (TICV)

  1. ToCV and TICV are both Crinivirus diseases in the family Closteroviridae. TICV was first detected in Orange County, California in 1993; ToCV in Florida in 1998. The viruses have since spread worldwide. Both viruses can seriously reduce tomato yields. They can be mistaken for magnesium or nitrogen deficiency, physiological disorders or pesticide damage, which appear very similar. They require the whitefly vector. They are not seed-borne. Although tomato is the major economic host for both these viruses, they can infect a range of other plants including some common weeds.
  2. See page 55 of the Seminis Tomato Disease Guide for an image of Infectious Chlorosis Virus (TICV). It does look like what we have. Vectored by whitefly only. Symptoms start on older leaves as interveinal yellow blotches, while veins remain green. The interveinal yellow patches can become white or die and be brittle. Symptoms can easily be mistaken for problems caused by poor growing conditions, aging or nutrient deficiency.

    Silverleaf whitefly from http://www.ars.usda.gov/is/graphics/photos/index.html
    {{PD-USGov-USDA-ARS}} Image Number K4600-7
    A one-sixteenth-inch long Silverleaf whitefly, Bemisia argentifolii. Category: Hemiptera  Photo by Scott Bauer.
  3. But these diseases are spread by whiteflies. We have had no sign of whiteflies this year or ever, in our hoophouse. Are we sure we don’t have whitefly? They are tiny (1 mm). Shake the lower leaves early in the morning and a cloud of whiteflies will rise, if they are there. We don’t see any.
  4. Dead aphid skins fall off some plants when they are shaken. Can aphids spread the virus? We did have a lot of aphids this spring. No, just whitefly.
  5. As ToCV is also known to affect southern peas, eggplants, lettuce, potatoes, pumpkin and sweet peppers, should we avoid those crops in that bed this winter and next summer? This list includes other nightshades (unsurprisingly), but also lettuce, beans and squash, so maybe also other members of those families, which covers almost everything, but notably not brassicas!! I hope we are growing brassicas in that bed this winter. Keep an eye on the peppers!
  6. Watching the How we can identify ToCV (Tomato Chlorosis Virus video from Mohammad in South Africa, ToCV seems less likely. We do not seem to have the main vector (whitefly), although the speaker suggests mechanical vectors are also possible for ToCV. Our plants look different. It is true that with the virus the chlorosis starts in the middle of the plant, as ours did. In the video, the affected leaves are distorted, buckled, and turned yellow all over, including the veins, even when the plant didn’t yet have much of an infection. As the disease spreads fast, the leaves look golden all over in just 2 weeks. The tops of the plants yellow and wilt. That’s not how ours are.

Chlorosis Cause 4: Other viruses?

  1. Tomato Yellow Leaf Curl Virus? It’s shown on the Clemson Extension document, HGIC 2222, Tomato Leaves Rolling?. Plants are very stunted. Spread by whitefly, not seed-borne. Can spread from tobacco and Jimson weed.
  2. Beet curly-top virus? The photo on page 51 of the Seminis Tomato Disease Guide looks more curly, stunted and less chlorotic than our plants, but not impossible. Spread by leaf-hoppers

There is no cure for tomato virus infections. Careful removal and destruction of the plants is recommended. Control of insect vectors and weed hosts is also important.

Leaf Chlorosis on Tropic tomatoes. Pam Dawling

Chlorosis Cause 5: Other causes?

  1. Texas A&M has a site on Disorders of Tomato Leaves. Nothing there looks like what we have. It did cause me to wonder about high salts.
  2. Missouri Botanical Gardens has A Visual Guide: Tomato Foliage, Stem & Root Problems. Not many virus pictures, though.
  3. Fusarium Rot fungus (pages 52-55) causes interveinal chlorosis, spreading up the plant from the lower leaves, and reddish-brown lesions in the vascular material of the main root and lowest part (only) of the stem, which would be evident when we pull up the plants. Not the same disease as Fusarium Wilt. Can be spread in soil, water, and through the air.
  4. Psyllid Yellows and Vein-Greening are bacterial diseases spread by tomato psyllids. Doesn’t much look like what we have, I think. Leaves curl outwards. Ours are curled in. Pictures in the 168-page Tomato Disease Field Guide
Salt Build-up

My current top four suspects:

A.    Magnesium deficiency
B.    TICV and we didn’t see the whiteflies
C.     High salt build-up in the soil
D.    Nematodes

Dealing with Flea Beetles on Brassicas and Nightshades

Young turnips (with flea beetles!) in need of thinning for cooking greens.
Photo Pam Dawling

This article will mostly be about brassica flea beetles, as our current struggle is getting fall brassica seedlings established. Brassica flea beetles are a different species from the ones that plague eggplant, and if you have one, you won’t necessarily have the other. Most methods for managing flea beetles are the same, regardless of the type of flea beetle and the crop they are attacking.

Unlike some cool-weather vegetables such as spinach, brassicas do germinate very well at high temperatures: the ideal is 77°F–85°F (25°C–29°C), but up to 95°F (35°C) works. Some people find refrigerating the damp seeds for 24 hours gives a better germination rate. Given enough water, summer seedlings will emerge in only three days. Once they have emerged, the bigger challenge begins. As well as temperature and moisture in the right ranges, the seedlings need protection from pesty bugs. We deal organically with flea beetles, harlequin bugs and, sometimes, cabbage worms. Our main defenses are farmscaping and insect netting.

Systems for growing transplants

The same systems you use for growing brassica transplants in spring may also work well for fall. Flea beetles can only fly a few hundred yards (meters). If you use flats, it can help to have them on benches in an enclosed shade-house, or outdoors, above the height of flea beetles. Ira Wallace of Southern Exposure Seed Exchange tells me 3′ (1 m) is high enough. Richard Jones, in his book Beetles, says flea beetles can jump at least a hundred times their body length.

Brassica seedlings under Proteknet.
Photo by Bridget Aleshire

We use an outdoor nursery seedbed and bare root transplants, because this suits us best. The nursery bed is near our daily work area, so we’ll pass by and water it. We’re always relieved to close the greenhouse transplant season in May, as we no longer need to water little plants many times each day to keep them alive. Having the seedlings directly in the soil drought-proofs them to some extent; they can form deep roots and don’t dry out so fast.

If you have no small troublesome pest insects, you can use shadecloth (up to 50%), which also keeps out large insects if well anchored to the soil. If you have flea beetles you will need covers with no sizeable holes, and you will need to close any gaps, either by burying the edges of the fabric, or weighting them down with sticks, jugs of water, or rocks. You can use clothes pins or binder clips to close any accidental holes (or sew them up with synthetic thread).

Rowcover can make the seedlings more likely to die of fungal diseases in hot weather — good airflow is vital. In warm weather, I prefer netting to keep bugs off, because it lets in lots of air. We use insect netting (ProtekNet) on wire hoops.

Biointensive integrated pest management (IPM)

This is a step by step approach that tailors strategies for each situation. The goal is to reduce pest damage of crops to an acceptable level, while minimizing the effects of pesticides on crops, workers and the wider environment. The focus is on restoring and enhancing natural balance and resilience to create healthy plants and soil better able to withstand attacks. Bio-intensive IPM includes controlling pests by physical and mechanical means (preventing the pest from reaching the crop, or removing the pest from the crop).

Start with preventative methods, monitor for pest levels, and if needed, take action via physical and mechanical methods, only turning to biological controls when other methods are insufficient.

 

  1. Prevention (cultural controls)

In your plans, minimize opportunities for pests to get out of control. Include such strategies as caring for the soil, minimizing soil compaction and hardpan layers, adjusting soil pH to suit the crops being grown, planting resistant, pest-tolerant, regionally adapted varieties, growing strong plants, maintaining good sanitation, promptly removing and destroying pest-infested plants, ensuring that transplants are pest-free before planting out.

 

  1. Avoidance (physical controls)

After growing the healthiest plants possible, the next stage is taking actions to reduce the chances of a specific pest taking over. All these methods reduce problems without adding any new compounds into the soil:

Crop Rotation Pinwheel

Use good crop rotations so that it’s hard for pests in the soil to find new host crops; plant successions of the same crop distant from each other, and each harvest day, pick the newer crop before the older one to minimize transfer of pests to the new planting; remove pest habitat; grow transplants in a protected greenhouse and plant out once the starts are large enough to withstand most pests.

Netting with small holes is better than rowcover for physically excluding pests in hot weather, as airflow is better. ProtekNet Pest Control Netting from Dubois Agrinovation is made of clear high-density polyethylene, polypropylene or knitted nylon, with UV resistance and a lifespan of eight to ten years (a lot longer than rowcover). Although it is not cheap, it is durable, given moderate care, and is easy to drape. Its light transmission is 90%. The 25g, 47g, 56g, or 70g mesh will protect against flea beetles and bigger insects. Netting also lets water through and protects crops against weather damage.

Bare root transplants growing outdoors under insect netting.
Photo Pam Dawling

Netting is best held on hoops above the plants so bugs can’t lay eggs or feed on the leaves through the holes. We remove netting about three weeks after transplanting brassicas, once the plants are big and sturdy. We also use this netting against flea beetles on eggplant transplants, removing it when the plants flower and need pollination. As we transplant, we hose the eggplants with a jet of water to dislodge any flea beetles already there, while someone else follows immediately behind to spread the cover and batten it down quickly with sticks. Collars around each transplant can be used to repel cutworms and cabbage root fly.

Mixed crop plantings (intercropping), hedgerows, field borders and farmscaping (intentional planting of suitable flowers that attract beneficial insects) can help maximize the diversity of insects and other beneficial organisms and avoid problems. We plant sweet alyssum in our spring broccoli patch to attract predators of aphids and caterpillars. Expect to plant 5% of the crop area to insectaries.

An insectary circle in early June. The flowers will attract beneficial insects.
Photo Pam Dawling

Provide habitat for bats, insectivorous birds, spiders, birds of prey and rodent-eating ground predators (snakes, bobcats).

Physically remove pests by handpicking, spraying with a strong water spray, flaming, vacuuming or by using a leaf-blower to blow bugs into a collecting scoop. Covering the soil with plastic mulch does reduce the problem.

  1. Monitoring

Just because a pest appears does not mean you have to kill it. The action level is the point at which the losses from the pest warrant the time, money and ecological disruption put into applying control measures. If flea beetles get your radish leaves, no one need know about them!

Make a habit of walking around weekly to scout for trouble as well as for natural enemies of pests. Scout vulnerable crops daily at critical stages. Learn to recognize bugs of all kinds and understand their lifecycles and enemies. Take a hand lens. Use a red LED headlamp for nighttime scouting. Photograph or capture insects you are unsure about and identify them from websites or books such as Whitney Cranshaw’s Garden Insects of North America.

Garden Insects, Whitney Cranshaw. Stock Image

Good record keeping helps improve effectiveness. Record pest names and numbers, date, crop, location, which input (if any), relative success of your action, comparison with methods used previously and overall evaluation.

Use weather forecasting to help determine when pest outbreaks are more likely. Use any available online pest-specific forecasting sites. These sites combine scouting and reporting of outbreaks with weather forecasts of temperature and wind direction to make a forecast map.

Keep a phenology chart to predict the likely arrival of key pests. Phenology is the study of seasonal and yearly variations in climate by recording regular plant and animal life cycle events each year. A visible change can be used as an indicator that another species is also likely to be changing. For example, we expect brassica flea beetles when the redbud blooms.

Traps

Set traps and lures. Although these may not significantly reduce the pest population, they are useful for indicating whether a certain pest is on your crops, so that other measures can begin as early as possible.

 Flea beetles can be trapped with a vacuum cleaner, or inside a bucket coated with Tanglefoot paste (hold the inverted bucket over the plant, tap it and catch the jumping beetles in the goo). A flea beetle trapping method I have not yet tried is to fill clear or white plastic bottles with water, cap them, coat the outside with sticky Tanglefoot compound around the middle two-thirds and set the bottles every 15′ (5 m) along the row under hooped covers. The water warms during the day and attracts the flea beetles at dusk. In four days you can expect to have caught almost all of them.

 Plant perimeter trap crops to lure pests from the food crop. Cleome attracts harlequin bugs, which can then be shaken off the tall flower heads into a bucket of soapy water. A row of pungent mustard greens can be used to lure brassica flea beetles. Once your trap crop is successful, you need to deal with them before you create a flea beetle breeding ground. Flaming the mustard plants is one possibility. If you have poultry that likes eating flea beetles, you could cut off some of the leaves and carry them to the chicken run.

Push-pull pest control
  1. Suppression

When the established action level for a particular pest has been reached, and prevention and avoidance strategies have been exhausted, biological, microbial, botanical, mineral (and for non-Organic growers, chemical) control measures can be used to reduce or eliminate that pest or its impact while minimizing environmental risks.

Design a series of measures that work together, to ensure that one action does not mess up another. Choose the least toxic materials and the least ecologically disruptive methods. Be aware of sensitive areas, such as waterways and habitat of vulnerable species. Be aware of better times to spray, eg for materials that kill honeybees, spray in the very early morning or at dusk when bees are not flying. For compounds that break down in sunlight, spray at dusk for maximum effectiveness and minimum amounts.

Bad damage from Mexican bean beetles on these bean leaves. Beetles will also attack the pods after a while, making them inedible.
Photo Wren Vile
  1. Biological control involves either introducing beneficial predators or parasites of the pest species, or working to boost populations of existing resident predators and parasites. Before we started buying the Pediobius wasp to deal with Mexican bean beetle, we used to plant more successions of beans, and flame the old plants when the pest count got too high. Most years we buy the Pediobius wasp parasite of the Mexican bean beetle. Some years populations are not high enough for us to need the parasites. Hb nematodes will control flea beetles, as will the braconid wasp Microctonus vittatoe Muesebeck.
  2. Microbial controls include fungi, bacteria, and viruses that kill pests. Bt (Bacillus thuringienisis), a species of bacteria, is the best-known microbial control. One strain kills caterpillars, another mosquitoes, another Colorado potato beetles. Spinosad is a fermentation product (no longer live material) of a soil microbe containing an enzyme that kills thrips, leaf miners, most caterpillars and some other insects. It is effective at one-eighth the recommended strength, if you don’t need to annihilate every last bug. It breaks down in sunlight, so spray at dusk. We use it against Colorado potato beetles on our March-planted crop. The June-planted potatoes don’t need any CPB control beyond the hay mulch we roll out to keep the soil cool and moist. We have also used Spinosad against the vegetable weevil larva when they took over our winter hoophouse turnips and greens.
  3. Botanical controls use plant-based products for pest control. If no selective method works, flea beetles can be killed with neem oil (it degrades in UV light in four to eight days and must be reapplied if the organisms are still around), or with Spinosad, a broad-spectrum insecticidal enzyme produced by a natural, although rare, soil organism. Pyrethrum is a botanical insecticide effective against flea beetles as well as beneficial insects. It is slightly toxic to birds and very toxic to fish so must not be allowed to contaminate waterways. Pyganic is one brand name. Rotenone is a strong broad-spectrum insecticide with short-term results that I do not recommend. In Canada, rotenone products are no longer registered for any agricultural use. It is toxic to cold-blooded animals including fish, and other animals including pigs. Research found that exposure to rotenone caused Parkinson’s disease-like symptoms in rats and correlated with a higher incidence of Parkinson’s disease in humans.
  4. Inorganic (mineral) controls, also known as bio-rational disease controls, include oils and soaps. Insecticidal soaps are made from potassium salts of fatty acids. They are effective only on soft-bodied insects such as aphids, not beetles. Kaolin clay, besides being a protective layer on crops, can suppress feeding of striped cucumber beetles, flea beetles, thrips and grasshoppers.

A useful resource is Kuepper, G. Flea Beetle: Organic Control Options (IP389). ATTRA, 2015.

Weeds of the Month for July: Pigweeds (Amaranth species)

 

Redroot pigweed
Photo by: D.G. Swan, WSU CAHNRS and WSU Extension

In May, I wrote about galinsoga, a warm weather annual that dribbles out seeds from an young age. In June, I wrote about docks, tap-rooted perennials that are best tackled early in life. This month is the turn of pigweeds, warm weather annuals that put out seeds in a “Big Bang” as Chuck Mohler describes in Manage Weeds on Your Farm. Pigweeds are fast-growing, tall, erect-to-bushy weeds that respond to high levels of nutrients as found in gardens and crop fields. Like corn, they use the C4 photosynthetic pathway, which means they thrive in high temperatures and high levels of light. They avoid getting shaded by growing fast, and they tolerate drought. Their vulnerability is that they do not produce seeds until they have been growing for some time and have reached a noticeable height.

Green Amaranth/Calaloo, grown for cooking greens.
Photo Baker Creek Seeds

Pigweeds are amaranths, a family that includes valuable food crops used for grains and greens, as well as dreaded weeds such as Palmer Amaranth, Waterhemp and Spiny Amaranth. Pigweeds are frost-tender, but if you have a long enough frost-free period, one plant can produce over 200,000 seeds.

Species of pigweeds

Mark Schonbeck has written a profile of pigweeds on the eOrganic site. He provides a list of eight unwelcomed pigweed species:

Silver Queen sweet corn with wilting pulled pigweed amaranth. Corn is a C4 crop, amarnath (pigweed) a C4 weed. Photo Kathryn Simmons.

Our experience with redroot pigweed in sweet corn

When I first encountered pigweed, I was told they were more-or-less impossible to deal with. Once I learned from Manage Weeds on Your Farm that, as tender annuals, they die with the frost, and as Big Bang weeds, they produce no seeds during most of their growth (unlike galinsoga!), I started a program of pulling them in our sweet corn patches. We used to grow a lot of sweet corn, and this tall crop, taking about ten weeks to mature the harvest, is a good habitat for pigweeds. We cultivate our sweet corn two weeks and four weeks after sowing, then don’t come back until the corn is ripe. This is an excellent window for pigweed to mature in! We started pulling the huge pigweeds each time we harvested corn. Inevitably, the weeds were right next to the corn plants, where our hoeing had failed to dislodge them. We found that if we put one foot against the base of the corn stalk and grasped the pigweed firmly and pulled up, we could usually tug them out. This won’t work if your soil is a tight clay, and if the pigweed breaks, the stem will branch and regrow. Most times, we harvest a patch of corn for two weeks and then disk or till it under. Usually we are turning the crop and weeds under before the regrown pigweed has had a chance to set seed.

Here is a video about Redroot Pigweed:

https://www.youtube.com/watch?v=Muqv3D-EujI

Economic weed thresholds of pigweed

Mark Schonbeck reports:

“Economic thresholds (weed levels that cause a 5% yield loss) for pigweeds emerging with corn and soybean crops have been estimated as low as 0.2–0.5 plants per 10 square feet, and 2–4 plants per 10 square feet for weeds emerging after crop seedlings have several leaves (Costea et al., 2004). In Ontario, redroot pigweed that emerged in corn at the 3–5-leaf stage at populations of 0.5–2.5 weeds per foot of row reduced yields 10–30%, whereas pigweed emerging at the 7-leaf stage had little effect (Knezvic et al., 1994)”

Our experience was that our corn yields were good, and we had found a successful method to manage the levels of pigweed over several years. We were cultivating between the rows and undersowing with soy at 4 weeks after sowing the corn, so the pigweeds growing were only those very close to the corn stalks. I do picture that an understory of pigweed would have a serious effect.

Spiny Amaranth

Spiny amaranth – a weed to exterminate by careful pulling.
Photo Pam Dawling

Spiny amaranth has been designated the world’s 15th worst agricultural weed. We have twice eliminated spiny amaranth from our gardens for a number of years, and then had it return. The seeds can remain viable in the soil and regrow when they are exposed to light. Although not as tall-growing as redroot pigweed, spiny amaranth has other ways of succeeding against those who would remove it from their crops: The nasty 0.5” (13 mm) spines (borne in opposing pairs at each leaf node) are not very visible among the branches, and are close enough together to make grasping the stem difficult.

The leaves of spiny amaranth are a darker green than redroot pigweed and have a V-shaped mark in a different color. Spiny amaranths can produce even more seeds than redroot pigweed: 235,000 each. Beware importing animal manure from other farms, and even gravel. I have seen a spiny amaranth germinate in a fairly large gravel pile brought in for road repairs.

Six methods of tackling pigweeds

Mark Schonbeck lists six methods of tackling pigweeds in organic production systems, and recommends using a combination of:

  • Cultivation, flame weeding, and manual removal 2-3 weeks after emergence
  • Stale seedbed
  • Mulching
  • Crop rotations that vary timing of tillage and other operations [our sweet corn was one year in 3 or4]
  • Cover crops and competitive cash crops
  • Measures to prevent or minimize production of viable seeds

Pigweed Flea Beetle

Disonycha glabrata – Pigweed Flea Beetle.
Photo from Bug Guide.net

Pigweeds even have their own striped flea beetle, Disonycha glabrata from the Chrysomelidae family. It is a large flea beetle. More the size of a striped cucumber beetle, but with a reddish thorax. It feeds on Redroot Pigweed (Amaranthus retroflexus) and other amaranths, so we never even try to grow salad amaranths as the leaves get riddles with holes. The first larval stage lasts 3.6 days, the second 2.6 days, and the third 2.9 days.  It spends 13.5 days in the soil.

Another Weed Management Resource

The book Steel in the Field, available as a downloadable pdf from SARE

Steel in the Field: A Farmer’s Guide to Weed-Management Tools. 1997. Edited by Greg Bowman. Sustainable Agriculture Research and Education (SARE). This book is a farmer’s guide to weed management tools using cultivation equipment.

Capture hornworms, and watch the film Six Inches of Soil

Large (4″/10 cm) tobacco hornworm on the ground.
Photo Pam Dawling

Hornworms

Hornworms just started to arrive on our hoophouse tomatoes and so we have started to capture them. We have tobacco hornworms on our farm, which was a tobacco farm over 57 years ago. They have 7 diagonal stripes on each side and a red posterior horn.  Tomato hornworms have 8 chevrons on each side and a bluish black horn. So if your hornworms look different from ours, you may have the tomato hornworm.

See my earlier posts

Hunting Hornworms on Tomato Plants

Dealing with Hornworms on Tomato Plants

When I saw the batch of new ones that my colleague Raen had photographed, I was reminded of those tests online to make sure you aren’t a robot “Click all the squares with. . .  ‘, and so I decided to make our own.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Click all the squares with hornworms in. Nothing will happen, it’s just for fun and to help us all get better at spotting them lurking in the foliage.

Movie: Six Inches of Soil

On a completely different topic, I enjoy following the farmers at Lynbreck Croft in the Cairngorms of Scotland. I’ve introduced Lynn and Sandra and their book Our Wild Farming Life here previously. Earlier this month Sandra and Lynn posted some updates including them waking on June 6 to the sight of fresh snow on the mountains.  They hosted a local showing of the film about Regenerative Farming, Six Inches of Soil. Click to see the trailer, and consider how you might one day host a screening, as someone in New Zealand has done. There were six in the UK today!

Here’s the information from Lynbreck Croft’s website

Six Inches of Soil is a story of courage, vision and hope. 

Story of the Film — Six Inches of Soil

Watch the trailer here on You Tube

“Our film, Six Inches of Soil, tells the story of remarkable farmers, communities, small businesses, chefs and entrepreneurs who are leading the way to transform how our food is produced and consumed.

Agroecology is an approach to farming that includes ‘regenerative’ farming techniques that work in harmony with, rather than against nature. It focuses on local food systems and shorter supply chains. The advantages are numerous: we get to know who is growing our food and how, farmers get paid a fair price and have the satisfaction of producing healthy food in a healthy environment.  Agroecology may also be our best chance in the face of climate change: it keeps carbon in the ground and creates resilient systems in the face of climate uncertainty.

Six Inches of Soil tells the inspiring story of young British farmers standing up against the industrial food system and transforming the way they produce food – to heal the soil, our health and provide for local communities.

There are approx.178,000 farmers working in the UK who manage 71% of the UK’s land, providing half of the food we eat, we import the rest. Current “industrial” mainstream farming practices significantly contribute to soil degradation, biodiversity loss and climate change. Regenerative farming practices, (within an agroecological system) promote healthier soils, provide healthier, affordable food, restore biodiversity and sequester carbon.

Six Inches of Soil is a story of three new farmers on the first year of their regenerative journey to heal the soil and help transform the food system – Anna Jackson, a Lincolnshire 11th generation arable and sheep farmer; Adrienne Gordon, a Cambridgeshire small-scale vegetable farmer; and Ben Thomas, who rears pasture fed beef cattle in Cornwall.

As the trio of young farmers strive to adopt regenerative practices and create viable businesses, they meet seasoned mentors who help them on their journey. They are joined by other experts providing wisdom and solutions from a growing movement of people who are dedicated to changing the trajectory for food, farming and the planetOur farmers will have to navigate a broken food system, farm in a landscape degraded by industrial agriculture and learn how to reconnect people with the soil, where their food comes from and how it is produced.

We don’t shy away from tackling complex and thorny issues. This includes exploring the connection between food and health, food poverty and affordability, the role of animals in the farming system, Britain’s hugely unequal system of land ownership, barriers to new entrant farmers especially from diverse backgrounds and whether there is a place for carbon offsetting on farms.

Alongside hard-hitting facts, we also convey what it feels like to farm agroecologically – to farm with authentic connection with the land, changing seasons and the environment, to produce food for people you know and care about in the local community: to spend your days with your hands in the soil.

The film looks at the history of British farming and asks “How did we get here?” through a short animated chapter that brings the audience up to speed with the industrial heritage of farming and the solutions that are within reach.

We show that agroecological farming is not simply a job, but a way to live values and engage in practices which not only nourish the planet but also the farmers themselves.”

 

2024 Spring Spinach Trials and previous ones

Our sparse spring 2024 late spring spinach variety trial.
Photo Pam Dawling

I have conducted trials of spinach varieties before, such as when our long-time favorite Tyee was dropped by the market. Now we need to look again.

Winter 2017-2018 spinach trials

February 5 photo of our 2017-2018 winter hoophouse spinach variety trial.
Photo Pam Dawling

We compared Avon, Reflect, Acadia, Escalade, and Renegade in the 2017-2018 winter in our hoophouse and outdoors. We were looking for a dark-leaved savoy type, with good cold tolerance and good bolt-resistance once spring arrives.

Our observations for the hoophouse were

  • Renegade made fast early growth in November and December
  • Acadia and Escalade won on early harvests (December and January).
  • The smoother-leaved Renegade had thinner leaves 4/10, and therefore a lower weight yield.
  • Acadia and Escalade won in the hoophouse on 4/24, for bolt resistance and thick leaves
  • Acadia won on bolt-resistance in the hoophouse on 5/1. Escalade was not far behind.
  • Reflect won on 4/25 over Avon on bolt-resistance in the 4th hoophouse planting.
  • Acadia won on 4/25 on bolt-resistance in the 5th hoophouse planting (late January).
  • There was no clear winner between Reflect and Avon on bolt-resistance in the late hoophouse transplanting from the 4th and 5th sowings.

For outdoor spring plantings:

  • Avon won on productivity over Renegade on 4/26
  • Reflect won over Acadia, Escalade on 3/21 and 4/26.
  • No winner between Avon and Renegade on 5/2
  • Reflect won over Avon on 5/2.
  • Reflect and Acadia won over Escalade for productivity on 5/2. Of the two, Acadia had better color.
  • Escalade may have been more bolt-resistant.

I also wrote about Success with Spinach for Fall, Winter and Spring. That post includes tips for growing spinach, as well as observations on varieties going into the winter.

From that complicated picture we could have chosen different varieties for different times and places, but we came down in favor of Acadia every time, with Escalade as a close second. Now I hear Acadia is being withdrawn and we must switch again.

Earlier winter spinach trials

Tyee spinach in our hoophouse in October 2002. Photo Twin Oaks Community

For those wanting to dig deeper, here are my earlier blogposts about spinach variety trials

Oct 4, 2016: Three spinach varieties (Tyee, Avon, Chevelle)

October 2016:  Sowing Tyee, Avon, Chevelle

Feb 21, 2017 : Spinach overwintered in a coldframe; Transplanting the last Tyee, alongside Reflect and Avon in spring.

February 6, 2018Spinach Variety Trials (Tyee, Chevelle, Avon, Reflect, Renegade, Escalade and Acadia) and Planting Plan. Details of the varieties.

April 10, 2018: Spinach Trials Update

2024 Spring Spinach Bolt-Resistance Trials

Meanwhile I agreed to trial five spinach varieties for bolt-resistance. It would be gratifying to have a spinach variety more resistant than Acadia. I sowed Sunangel, Tarsier, Seaside, Kolibri and Lizard to compare their bolt-resistance. Sowing from mid-March to early April is much later than I would normally do here in central Virginia, so it would be a real test. I had 4 sowing dates each a week apart and three reps of each variety to even out any “unfairness” due to differences between bed edges and middles. It was all over by June 7.

I kept a spreadsheet, and included air temperature high, rainfall, irrigation, and after a while, soil temperature every Friday when I did my monitoring.

I didn’t get to harvest any spinach from this trial, as the number of plants was small, but I did see some clear differences in bolt-resistance. Sunangel is clearly the least bolt-resistant, by a long way. Kolibri is clearly the most resistant of the five under our conditions. Tarsier was second to Kolibri after a gap.

Bolting Sunangel spinach on April 21.
Photo Pam Dawling

We had challenging conditions:

During March we had a lot of rain, and we were unable to till in the wheat cover crop and prepare the bed and sow when we hoped.

I pre-sprouted the seed for the first sowing (“3/15″) for a week, and sowed it 3/22, the same day as the second sowing. By then we had tilled the too-wet bed roughly.

A week later, 3/29, some cover crop was poking through and regrowing, and the soil was still very wet.

A week after that (4/5) the soil temp was 58F. Germination was poor for all varieties in the first three sowings. We made the fourth (last) sowing. The weather turned to drought (the bed got overhead irrigation once a week). Air temperatures reached 89F, although the soil was still 60F.

All germination rates were poor, some very poor, which I attribute to the conditions. The first sowing of Sunangel started bolting 4/21.

By 4/26 the soil temp had reached 70F

After three weeks of no rain, we got a lot, 1.8″ one week, 2.1” the next. Daytime temps reached the high 80’s.

On 5/31 we got an outbreak of what I think was downy mildew. All varieties were equally affected. The second sowing of Sunangel started bolting.

It was another week before the first sowings of the other varieties started bolting. Kolibri was noticeably most resistant in all sowing dates.

Our winter favorite, Acadia, is currently still available from High Mowing, Pinetree and Harris. Escalade and Kolibri are available from Stokes. Kolibri is good at bolt-resistance, but not DM resistance and I’ve no idea how it does in the winter. We can try it next winter. Space is the variety often grown commercially. It has high DM resistance and claims to be for all seasons.

What triggers bolting?

Hoophouse spinach Top row: bolting Renegade; nearer row: Escalade.
Photo Pam Dawling

I wrote a post a few years ago What makes vegetable crops bolt and how can I stop it?

This article from Michigan State University also does a good job of explaining how cold temperatures trigger bolting (flowering) in spinach and other crops.

Harvesting Alliums (onions, garlic and relatives)

Onions curing and drying in strings.
Credit Southern Exposure Seed Exchange

The allium family includes all kinds of onions, garlic, leeks, perennial onions such as potato onions, and also less well known alliums, mostly perennials.

This is the time of year for harvesting most alliums except leeks. (It’s the time for planting out leeks for fall and winter harvests.)

I have a whole series of Alliums for the month posts. Here’s a link to Alliums for June. It includes the starter for the list I provide here, of the relative timing of harvests for various alliums.

Order of Allium Harvests

Our allium harvests generally occur on these dates. Your dates will differ but you can expect this order of harvests:

  1. Nov 18–May 10: Onion scallions in the hoophouse
  2. Mar 15–May 31: Garlic scallions
  3. May 7–May 28: Garlic scapes
  4. May 10–Jun 30: Onion scallions outdoors
  5. May 25–Jun 10: Green bulb onions (Allium cepa)
  6. May 30–Jun 8: Hardneck garlic
  7. May 30–Jun 11: Potato onions ( cepa aggregatum) planted in fall
  8. Jun 6–Jun 25: Potato onions planted in January and February
  9. Jun 10: Shallot bulbs (cepa aggregatum), fall-planted. They are not fully hardy in zone 7a. I recommend storing bulbs and replanting in early spring instead
  10. Jun 11–Jun 12: Softneck garlic bulbs
  11. Jun 11–Jul 11: Bulb onions sown in fall, with slow spring-sown ones to Jul 26
  12. Jun 19–Jul 2: Cipollini (cepa cepa) Small bulb onions grown in a hoophouse from spring transplants
  13. Jun 30–Jul 5: Elephant garlic ( ampeloprasum ampeloprasum) We stopped growing this when too many winter-killed
  14. Jul 1–Jul 8: Shallots from bulbs refrigerated over the winter and replanted in early spring
  15. Jul 1–Jul 15: Cipollini outdoors from spring transplants
  16. July: L’itoi (A. cepa aggregatum). This peppery little perennial clumping onion sends up edible shoots in early July.
  17. Jul 4–Jul 30: Shallots from seed started in late January, plugs transplanted in March. Harvest 4–8 weeks later than those from bulbs replanted in October
  18. July–September: The small red-purple bulbils of Egyptian onions can be pickled. Earlier in the year, before the bulbils appear, harvest the tasty, succulent leaves of this very hardy perennial.
  19. Spring, summer, fall according to size: Welsh onions ( A. fistulosum) are non-bulbing, hardy perennial onion greens, larger than chives and scallions. Japanese bunching onions are similar. Can be sown in fall or spring. Clumps can be divided and replanted
  20. Sep 6: Shallots direct sown outdoors in February and March

Here’s some details on harvesting some of the smaller alliums

Harvesting onion scallions

Scallions ready-to-harvest.
Photo Pam Dawling

From around May 10, through June, our outdoor onion scallions are big enough to harvest (just as the hoophouse ones finish up!) We start these from seed in January and February and transplant as clumps in March and April. In cooler climates, you can schedule harvests through summer, but we cannot get good quality ones here after late June. It’s good to develop an efficient harvest method with little scallions or it takes way too long. To harvest, loosen the soil with a digging fork, then lift out a clump. Deal with scallions in bunches as much as possible, rather than one at a time. Shake the plants, and trim off the roots and the ragged tips. Holding the bunch in one hand, pass the scallions one at a time to the other hand, separating them and pulling off a single outer leaf, not more. Don’t fuss with them too much. Next set the scallions in water in a small bucket, to clean themselves while you work on the rest. If you are going to band them, start out with a bunch of rubber bands around three fingers on the hand that holds the bunches (leaving the forefinger free for tasks demanding dexterity). When you’re ready to band them, use the other hand to pull a rubber band into position. When the bucket is full enough, dunk the scallions up and down, and transfer them to a clean bucket with a small amount of water to keep them fresh.

Harvesting garlic scallions

A healthy patch of garlic scallions in spring
Photo credit Kathryn Simmons

Garlic scallions (small whole garlic plants) provide our first allium harvest of the calendar year, starting in mid-late March and continuing (if we have planted enough) into May. Some people cut the greens at 10″ (25 cm) tall and bunch them, allowing cuts to be made every two or three weeks. We prefer to simply lift the whole plant once it reaches about 7″–8″ (18–20 cm) tall. You may need to loosen the plants rather than just pulling. The leaves keep in better condition if still attached to the clove. Trim the roots, rinse, bundle, set in a small bucket with a little water, and you’re done! Garlic scallions can be sold in bunches of three to six depending on size.

Harvesting garlic scapes

Harvesting garlic scapes
Photo by Wren Vile

Another spring allium harvest is garlic scapes (the firm, edible flower stems of hardneck garlic).  Here scapes appear when tulip poplars flower. In a warm spring, that can be the end of April. Garlic scape arrival is partly temperature dependent. We harvest scapes two or three times a week for about three weeks, until there are no more. At the Roxbury Agriculture Institute at Philia Farm in New York State, they wait until the scape has curled round, then cut it off. We harvest ours sooner than that, in order to let the bulb grow as big as possible. We pull our garlic scapes to get the most out ! In our climate, the appearance of scapes indicates the garlic will be ready to harvest in three weeks. I’m not sure if the same timing works everywhere, so keep records and you’ll learn what to expect. Exactly how day-length and temperature interact as triggers for scape and bulb harvest dates, I don’t know. I’ve done some research, but haven’t found much solid info yet.  In general, plant flowering is triggered by some combination of enough vernalization (chilling hours — maybe 10 weeks below 40°F/4.5°C), plant maturity, temperature and photo-period (the relative length of day and night). In cold weather the plants suppress the flowering signal. The leaves perceive the amount of daylight, and when the temperature is also right, they trigger flowering by sending a signal (called Florigen) to the shoot tips. Florigen may be an actual compound, or may be some combination or ratio of several hormones produced by the plant. Almost all these factors are outside our control once the plant is in the ground, so the best we can do is pay attention and be ready to act.

Harvest garlic bulbs and bulbing onions

(see Alliums for June) I won’t go into details here, as I’ve done that previously.

240 heads of garlic drying in Tenax fencing.
Photo Sierran Farmer

Harvest small potato onions

produced by large ones planted in September.

Yellow Potato Onions.
Photo Southern Exposure Seed Exchange

Harvesting cipollini

(aka cocktail onions, boiling onions, pickling onions)

Red Marble cipollini.
Photo Fedco Seeds

These small, attractive onion bulbs can be easier to grow in marginal onion climates than full-sized onions or can be an additional allium crop. The larger ones can be used as fresh bunching onions. All may be cured. Cipollini naturally have more sugar than most onions, which makes them ideal for caramelizing or roasting whole. The scheduling and final size of your cipollini will depend on your latitude and temperatures.

Weed of the month: Docks in June

Dock weeds flowering and seeding in early June.
Photo Pam Dawling

 This is the second of my once-a-month series of posts focusing on weeds. One weed that is making itself very evident on our farm in late May and early June is the dock. We have both the broadleaf dock, Rumex obtusifolius L. and the narrow-leaved or curly dock, Rumex crispus L. Docks are in the buckwheat family.

Docks are tap-rooted perennial weeds, requiring different approaches to last month’s weed, the fast-seeding annual galinsoga.

Cover of Manage Weeds on Your Farm
SARE

See the excellent information on docks in the book, Manage Weeds on Your Farm: A Guide to Ecological Strategies, By Charles Mohler, Antonio DiTommaso and John Teasdale. Click the link to read my review. It’s a book worth having on your shelf and it’s also available online from SARE  It explains how to tackle various types of weeds in an ecological way and then profiles many individual weeds. With good clear photos of weeds at various stages of their lifecycle. Here you can find out what dock seedlings look like, and go and hoe them out before they get too big.

Another resource on ecological weed management is the ATTRA publication Sustainable Weed Management for Small and Medium-Scale Farms

When dock seeds germinate they first develop a rosette of leaves close to the ground. The rosette grows quite large (leaves can be 12″ by 6″ with broad-leafed docks, 12″ x 2.5″ for narrow-leafed docks), at which point most of us cannot simply pull the dock out as the tap root will be sturdy and long. You will need a digging fork or a shovel to get the root out. As with other tap-rooted perennial weeds, if the root breaks, the part remaining in the soil can regrow. The short, vertical underground stem that attaches to the roots regrows readily. In spring, new plants can also grow from fragments of the true root.

Broad-leafed docks have branching taproots, while the narrow-leafed docks have a single root, with almost no branches. If left to their own devices, the leaves become speckled with red  and the plant puts up a tall stem with clusters of inconspicuous reddish flowers. The flowers mature into winged fruits surrounding three-sided glossy reddish seeds.

Dock as a rosette. Photo University of Maryland Extension

Docks can become established in uncultivated but fertile areas, especially along edges of pastures or areas with long-term cover crops. frequent mowing before docks get a chance to grow large can help other plants to out-compete the docks. The key is to provide enough nitrogen for your crops but not more, or the docks will suck it all up! Vigorous crops can out-compete docks for light (part of why docks do well on edges where they have no competition).

If docks get too big and have flowering heads or even seed heads, it is best to dig them out and take them away. This is a good time of year for that, before the seeds mature and scatter. If I dig just one or two docks, I put them on the driveway to dry out and get road-killed by vehicles rolling over them. If we take advantage of a day with lots of help, especially after rain when the soil is easier to dig, we take wheelbarrows and make a team sport of it, digging all the docks from one area. We have a special place under trees that we call the End of the World, where we pile noxious weeds. The shade discourages them from regrowing, as does the sheer weight of the weeds we pile up.

On a larger scale, if a whole field has become infested with dock, say a pasture that you want to convert to growing annual crops, then stronger measures are called for. Disk or plow the field in midsummer (now!), and repeat the cultivations whenever the weather is suitable for drying out fresh root pieces that will get brought to the surface. I would not normally advocate repeated tillage and leaving soil bare, but annual crops are no match for established perennial weeds.

Narrowleaf or curly dock with a stem of still-green flowers. Photo University of Kentucky Dept of Plant and Soil Sciences

If you are using a rototiller, be sure to work down to a depth of four inches. If you till shallowly, you might just severe the neck from the root, allowing the dock to regrow. Run your machinery slowly and get maximum chewing-up action. When you see new shoots with 2” leaves growing, repeat the tilling. This is the stage at which the regenerated plant has extracted lots of nutrients from the root piece and has not yet paid much back. Don’t wait longer!

Winter cover crops can do a lot to suppress new dock seedlings as well as regrowths. The growth rate of docks is slow-and-steady, the opposite of galinsoga! Tackle docks before they disperse their seeds. Once shed, dock seeds are initially dormant for some months. Germination occurs at 50°F–95°F (10°C–35°C) with 68°F–77°F (20°C–25°C) optimal for fastest germination. Cooler nights and warmer days help speed germination, as does light exposure, unless filtered through overhead trees, which decreases germination. Flushes of seedlings tend to germinate in spring and fall.

Seeds of broadleaf dock can remain viable for 40 years, and those of narrowleaf dock can live in the soil as long as 80 years! But the rate of seed mortality each year is quite high. Manage Weeds on Your Farm quotes one experiment in Ontario, when less than 15% of curly dock seeds and 1% of broadleaf dock seeds survived more than one year.

Large dock weeds in early June
Photo Pam Dawling

Docks that survive the winter as rosettes make new growth in spring (February to March) and flower in April and May. Seeds mature a mere 6-18 days after flowers open. If you see flowering docks, don’t delay!

Both dock species are relatively short-lived perennials, nearly all dying within 4 years. By that time, they may have produced over 240,000 seeds.

Dock leaves are edible by people and pigs, but not cattle, horses or poultry. They may be cooked like spinach and many people find them very tasty.

Success with Growing Watermelons

Crimson Sweet Watermelon. Credit Southern Exposure Seed Exchange

 Watermelons are delicious as a snack on a hot day in the garden, helping improve your heat tolerance.  If lightly salted to balance the electrolytes, they can cure dehydration. The seeds, if well chewed to break up the indigestible seed coat, can provide amino acids, fatty acids, vitamin E, potassium and phosphorus. Watermelons are easily digested and add fiber to the diet. Second only to tomatoes as a source of lycopene (said to prevent some cancers), watermelons are also an excellent source of vitamin C, beta carotene, folic acid, biotin, potassium, magnesium and citrulline (an amino acid important for healing wounds and removing toxins from the body).

Watermelon Varieties

Amish Moon and Stars watermelon. Credit SESE

Watermelons are all Citrullus lanatus. After trying several varieties, we chose Crimson Sweet (85d from transplant, OP), a 20–25lb (9–11 kg), striped, 10″ x 12″ (25 x 30 cm) oval melon. It has tolerance to some strains of Anthracnose and Fusarium, and according to Southern Exposure Seed Exchange, it promotes beneficial soil fungi that inhibit Fusarium. We saved seed for many years, selecting for size, earliness, disease resistance and flavor. See Fruit of the Month for September for more about choosing varieties. At this point, you have probably made your choice for this year, and may have them in the ground.

Watermelon Crop Requirements and Yield

Watermelons do best in free-draining light soils that warm quickly in spring. Ensure high organic matter content, sufficient boron and a pH of 6.5. Black plastic mulch, either the removable or the biodegradable kind, will speed growth and ripening. If you want to use organic mulches, put them around the plants after the soil has warmed up, or you will delay the harvest. Drip irrigation is better than overhead, as it reduces the chance of foliar diseases. Water well during fruit development, then cut back during the harvest period for best flavor and to prevent fruit bursting. We often run our irrigation at the same time as harvesting, so we can easily check for leaks.

If drainage is an issue, make ridges or raised beds before planting. You can use straw or spoiled hay in the aisles to absorb some of the water. Watermelons easily die in waterlogged soil.

There are on average 24 seeds/g, 670/oz, 11,000/lb, 24,200/kg. Crimson Sweet seeds are about half the size of others, so need only half as much seed.

Yield of Crimson Sweet and other varieties can be 460lbs/1,000 ft2 (227 kg/m2). For our 6,600 ft2 patch, (613 m2) we can expect an average of 3,000lbs (1,400 kg), whether 150 melons at 20lbs (9 kg) or 300 at 10lbs (4.5 kg). We have got as many as 300 melons from this area, using 2′ x 5.5′ (0.6 x 1.7 m) spacing. More on spacing follows.

Dried watermelon seeds in a paper bag.
Photo Pam Dawling

Sowing Watermelon Seeds

Watermelon seeds need a soil temperature of at least 68°F (20°C) to germinate, taking 12 days at that temperature, but coming up in a mere 3 days at 95°F (35°C). If direct seeding, station-sow 4–6 seeds 1″–1.5″ (2.5–4 cm) deep at the final spacing. Later, thin the emerging seedlings to one or two at each spot. Pests are more likely to attack plants stressed by planting in cold conditions. If in doubt, wait.

Transplanting is the way to go for early melons. It allows young plants to be raised in close to ideal conditions, and it gives the soil time to warm up. We use Winstrip 50-cell ventilated plug flats for this crop, or soil blocks. Cells should be at least 1.5″ x 1.5″ (4 x 4 cm). We put two seeds in each cell and after emergence we pinch off the weaker seedling. We sow 30% more cells than we hope to take to the field, which is another 30% more than we need to plant because of their fragility. Casualties with melons are usually fatal. (We expect casualties on planting day.) We sow April 26.

They come up very fast in our hot germination chamber. Once the seedlings emerge, they need maximum light and warmth, but not too much watering. We transplant at 15–19 days old. Four weeks old is about the maximum for watermelons — they start to get stunted if held too long.

Watermelon transplants in a Winstrip tray on May 2nd. Photo Pam Dawling

Transplanting Watermelons

Don’t rush watermelon transplants into cold soils, it’s better to wait — cold conditions can permanently stunt them. Once outdoor daily mean temperatures have reached at least 60°F (15.5°C) and the first true leaf has fully opened, you can plant them out.

We have found watermelons to be amongst the crops needing the most skill at transplanting. The stems are fragile, the roots respond poorly to disturbance, and spending extra time later replacing the dead plants is frustrating and doesn’t lead to early melons. It also requires the grower to produce lots of spare plants, which all take time and care.

Pulling a roll of biodegradable mulch.
Credit Wren Vile

We roll out drip tape, test it for leaks and then unroll biodegradable plastic over the drip tape and shovel soil along all the edges of the mulch. See our method of using biodegradable plastic, setting it out by hand. The next day we turn on the irrigation while planting. This helps ensure no one stabs the drip tape, and the plants can be set by the emitters. (Yes, you can still find them, even though they are under the plastic.) Watermelon transplants can easily get leggy in the greenhouse, so make holes deep enough to bury the whole stem as well as the roots. We use pointed trowels to punch through the plastic.

We drape netting or rowcover over hoops. This prevents the cover abrading the leaves, creates a volume of warm air around the plants and keeps insect pests away. A week after transplanting, we fill any gaps with more transplants or with a few seeds station-sown at each spot where we want a plant. Sowing pre-sprouted seeds will help make up for lost time if something has gone wrong.

Watermelon Spacing

Spacing can make a difference to size and yield, but not sweetness. There are widely varying recommendations, from 9 ft2 (0.8 m2) to 80 ft2 (7.4 m2) each! The area is the important factor, so choose a row spacing that works nicely for you and adapt your in-row spacing to give the area you want for each plant.

 


Watermelons growing on (torn) plastic mulch. A tented row with rowcover is in the background. Photo Nina Gentle

We used to transplant our watermelons 2′ (60 cm) apart in rows 10′ (3 m) apart. I read about watermelons only needing 10 ft2 (0.9 m2) per plant, so we switched to a spacing of 2′ x 5.5′ (0.6 x 1.7 m), 11 ft2 (1 m2), in order to fit more plants in the space and therefore get more first and second melons. The new spacing seemed fine and the total yield was in the right range. We have tried 2.5′ (80 cm) in-row spacing, some at 3′ (90 cm) and some at 3.5′ (1.1 m). These spacings correspond to areas of almost 14 ft2 (1.3 m2), 16.5 ft2 (1.5 m2) and 19 ft2 (1.8 m2) each. We didn’t keep records and didn’t notice a difference in size. A Brazilian study on Crimson Sweet found that 13 ft2 (1.2 m2) per plant gave the highest total yield, but 15–20 ft2 (1.4–1.9 m2) gave bigger melons.

Factors in Deciding Watermelon Spacing

Total yield (by weight): reduced spacing (to a certain point) increases total yield. Reducing plant spacing 50% may increase the total yield by 37%–48%, while reducing the size of each melon only 10%-13%. Reduced spacing does not decrease the percentage of marketable fruit.

Yield/plant (by weight): decreases at close spacing, sometimes because the number of melons per plant is reduced, sometimes because the size of the fruit decreases. It is not a linear decrease.

Size: reduced plant spacing sometimes affects melon size, but not in a linear way. Other (environmental) factors affect melon size. Bigger varieties are more likely to have their size affected by closer spacing than small varieties are. Small size is an advantage in some markets.

Number of melons/plant: decreases as plant spacing is reduced, but not linearly. At close spacings, the difference is negligible.

Number of melons/area (fruit density): increases with plant density. More plants = more melons.

Early yield: variety, early transplanting, good conditions and hot weather will provide more early melons. The first melon on each plant is the early harvest. More plants means more first melons. Plastic mulch produces crops a month before organic mulch. Spacing has no influence on the ripening rate.

Sweetness: the flavor of watermelon is not related to the size of the ripe melon or the plant spacing. Healthy foliage and long hot sunny days are the biggest factors in building good flavor. August has shorter days than July, and September’s days are even shorter, so don’t expect late-season melons to be as sweet.

Plant health: overcrowding can increase foliar diseases, reducing photosynthesis and sweetness.

Labor requirement: closer spacing = more transplanting. More melons = more time harvesting.

Watermelon with healthy foliage and a flower. Photo Nina Gentle

Clarify your goals and choose your variety and spacing accordingly. If your goal is the highest weight of watermelons for a given area, plant Sugar Baby at 10–11 ft2 (0.9–1 m2) each. If your goal is the highest number of melons, try them even closer! But if you like Crimson Sweet and want fairly large melons, try 15 ft2 (1.4 m2) if 12lb (5.4 kg) melons are an acceptable size (you might still get 15lb/6.8 kg melons!). Otherwise, use 20 ft2 (1.9 m2). Go up to 30 ft2 (2.8 m2) if you want big melons and can accept a lower total yield.

Ideally, the ground will be filled with foliage by the time the first blossoms appear so that the crops can intercept and use all the available sunlight. Given that the market is for early melons, and early ones are sweeter, having many plants (one early melon each), and having them optimally cared for, is important.

Caring for the Watermelon Crop

Remove rowcover from transplants after three weeks (wait longer with direct sown crops) and remove netting once you see female flowers. Pollination is now the critical step, not warming. Pull any big weeds. (Cultivate between the rows if you have bare ground.) Water regularly — drip irrigation set out at planting is the best way to go, as there will be less chance of fungal diseases than with overhead watering.

Watermelons have separate male and female flowers on the same plant, and insect pollinators are necessary. Many species of native bees pollinate watermelons, but augmenting them with honeybees will help pollination, which means bigger, better-shaped melons as well as more of them.

Weeding is important and needs to be completed before the vines run. If big weeds get away from you and pulling them endangers the crop roots, wade in with pruners and clip off the weeds at ground level. This prevents the weeds seeding, and lets the melons get more sunlight again. Do not turn over the vines when weeding — cucurbits don’t like that! Removing damaged fruit will help the good ones grow better.

See Fruit of the Month for September for information on pests and diseases, harvesting and choosing varieties for next year. this material comes from my book, Sustainable Market Farming, where even more info can be found!

Ripe watermelons are a treasure! Photo Nina Gentle

Cicadas – the real story for Virginia

Top: Annual cicada. Credit Bugwood.
Bottom: Periodical Cicada. Credit Eric Day

Cicadas

Despite hype, cicada double-brood emergence won’t affect Virginia, Virginia Tech expert says

https://news.vt.edu/articles/2024/03/ext-cicada-double-brood-emergence-wont-affect-virginia.html

There are annual (“dog-day”) cicadas that emerge every year. Annual cicadas have black-green coloring, while periodical cicadas have black-red-orange coloring.

Annual cicadas, although noisy and large, are not at all dangerous to people. In fact, they are edible, but I do recommend removing the wings and legs first, otherwise it’s too much like eating crunchy food wrappers. Well, I suppose it is eating crunchy food wrappers! The flavor is mild, and the texture creamy.

Annual cicadas can damage young trees, because the females make slits in the bark of pencil-thickness twigs to lay their eggs. The overall effect is like pruning back the twigs about a foot. Not a problem on a big tree, but to be avoided on young trees if possible.

How do you protect young trees from cicadas? Cicadas emerge from the ground in a pupal shell, which they climb out of when they’re ready, splitting the top of the skin. You may have seen these cast shells still gripping on to siding or boards or other things that could be mistaken for a tree. Before too many emerge, cover your vulnerable new saplings with netting, or fabric. If you are a gardener, you may have rowcover or insect netting that will be perfect. If not, you may have old bedsheets or nylon net curtains. Keep the plants covered until no more cicadas are emerging. Cicadas die after laying eggs (I wonder when the males die?)

If you get the chance, stop and watch as an adult cicada emerges from its nymph shell. At first the wings will be crumpled and bright pink. Gradually they will stretch out and dry. Here’s a great little time lapse video of the process. In real life, it takes a bit longer! Note that it is the adult emerging from the nymph, not the nymph emerging.

The hype this year has been about the periodical cicadas. In particular, doomsayers have been trying to panic us into thinking we are all going to be battling a combination of the 13-year cicada and the 17-year cicada in some places. Mostly it’s not true.

Doug Pfeiffer, professor and Extension specialist in the Department of Entomology of Virginia Tech. explains “They have evolved this strategy of emerging all at once in order to overwhelm predators, a defense strategy called predator satiation.

“Periodical cicadas emerge after either 13 or 17 years, both prime numbers,” said Pfeiffer. “That is an adaptation to avoid predators who might develop a converging lifecycle and emerge to eat them.”

Each type of cicada exists as several Broods. Blacksburg, home of Virginia Tech, is on the very edge of the range of Brood XIX (19), a population of 13-year periodical cicadas produced from eggs laid in 2011, resting underground since then. Virginians living south of Caroline County and east of the Interstate 95 are probably seeing and hearing Brood XIX by now. Virginians living along the North Carolina border, especially those in Brunswick County, should also be on the lookout. See the map from Virginia Tech.

Virginia map showing likelihood of finding periodical cicadas in each county. Credit Virginia Tech Extension Service

People in the red zone will get no periodical cicadas. People in the bright green zones will probably get them. Other Virginians are in the maybe zones.

And the scary double-brood? A brood of 17-year cicadas (Brood XII) will also emerge in2024 – in Illinois! Very little geographical overlap!

When it is all over, the dead cicadas lie on the soil, feeding it as they decompose. The eggs hatch into tiny wingless nymphs, which walk down the tree and bury themselves in the ground, sheltering until it’s time to go above ground again, eating nutrients from plant roots.

Here’s a chart of when you can expect periodical cicadas in your neck of the Virginia woods:

Chart of cicada broods in Virginia

We are home to the 17 year brood II, last heard here in 2013. due back in 2030.

And here’s a map

East Coast cicada dates

Cold-hardiness zone map, heat zone map and fruit chill hour requirements

 

Our pond iced over.
Photo Ezra Freeman

I was alarmed to hear on NPR that the USDA had issued a new map of winter-hardiness zones. It seemed so recent that we got an update! Relax! (Sort of!) It’s the same 2023 map that I reported on here in November 2023. What is new and worth a visit is the interactive map posted by NPR .

2023 USDA Cold-hardiness zones map

Enter your location and see a map with your zone on the previous 2012 map. Scroll down (it was not immediately obvious to me to do this. . . ) and you can see what zone that area is in now. Scroll further down and you can see the amount the 30-year minimum temperature average has changed since the 2012 map (which used the data from 1976-2005). In my case, Louisa, Virginia has got 3 Fahrenheit degrees warmer in winter on average, than it used to be. Good for keeping some perennials and annuals alive over winter; not so good for fruits requiring a certain number of chill hours, such as apricots.

Our grape rows from the north.
Photo Kathryn Simmons

Fruit and Nut Tree Chill Hours Explained

Apple trees and other fruit and nut trees need cold temperatures to be able to set fruit the following season. Chill hours are the cumulative number of hours during the winter, below a temperature of 45ºF. Nut and fruit trees need a specific number of chill hours each winter to regulate their growth. It is a cumulative total for the whole of the dormant season, whenever they happen. Chill hours are further explained on the Stark Brothers website where there is also this map.Click the link for the ability to zoom in on your location.

Chilling Hours map of the US, for fruit and nut tree growers. MRCC Vegetation Impact Program

Citrus fruits do not need any chill hours. At our farm, we get around 700-800 chill hours each winter. Any tree needing less than 700 will be well served by our winters! Redhaven peaches need 800 – a bit of a gamble. Honeycrisp apples need 800-1000, so they are not for us!

Deke Arndt, director of the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information says that winters are warming at a faster pace than other seasons.

Also, an increase in the quantity and quality of data collected at weather stations across the nation in recent years has helped to increase the overall accuracy of temperature readings. The 2021 data are more accurate than the 2012 data, so the difference (change) over that time is a bit uncertain.

Immature frosty cabbage. Photo Lori Katz

Scroll down the NPR page further, and after a reminder that your zone measurement is an average of the coldest yearly temperature in your area over the past 30 years, you can see a scatter chart of the actual coldest temperature each year from 1991 to 2020. The coldest here was -13ºF in 1996. In that same period, seven winters have had a minimum that was warmer than 10ºF. When you average those coldest nights in each of the 30 years, the average comes out at 4F here. That is, the average coldest night over 30 years was 4ºF.

Scrolling down further we see that puts us in zone 7a, where the average lowest temperature each winter is in the range 0ºF-5ºF. Next comes a reminder that this is only useful for plants that have to survive the winter.

The site focuses on ornamental perennials: You plant them once and they come back after each winter if they’re given the right environment to survive. Think things like trees, shrubs and woody plants. Hydrangeas, Azaleas and Lavender can survive our winters. The Windmill Palm grows in zones 7-11. It might survive here. But, anyway, I’m more interested in vegetables.

A stormy winter day, garlic, rowcovered spinach beds and our hoophouse.
Photo Wren Vile

However, it’s also true that the lowest winter temperature affects annuals that are overwintered to produce spring vegetable crops. Combine the information about your winter-hardiness zone with my Winter-Kill Temperatures of Cold-Hardy Crops list to see what vegetables it is worthwhile keeping in your garden over winter, and which ones will probably survive with rowcover. And which would need a hoophouse or greenhouse to survive.

On its own, your cold-hardiness zone can’t tell you what to grow in your area. For example, parts of Juneau, Alaska; Boston, Mass.; and Santa Fe, N.M are all in USDA’s Zone 7a, as are we in Louisa, VA.

Juneau has relatively temperate winters that are extremely wet, averaging over 80″ snow a year. Santa Fe is extremely dry, with much hotter summers than Juneau. Boston has temperate winters and temperate summers. It gets rain, but not nearly enough for Juneau’s rainforest plants to thrive. It gets heat in the summer, but is colder and wetter in the winter, preventing desert plants like cactuses and other succulents from thriving.

Because all these three cities rarely get below 0ºF each winter, they are all classified as zone 7a.

Vates kale with a freeze-killed center January 19 2018.
Photo Pam Dawling

Here are some things to keep in mind about winter-hardiness zones:

  • Your winter temperature can still dip below your hardiness zone. Remember, your zone is a measure of the average coldest night in 30 years. Some years are above average, others are colder!! Even much colder! In 2014, the temperature in St Louis (zone 7a) dipped three half zones below St. Louis’ hardiness zone, to -10º F. So be alert to the threat of extreme cold snaps. And find a way to keep your plants warmer until the snap passes.
  • The hardiness map says nothing about the frequency of extreme cold weather. A plant or an animal can survive an occasional short dip to a temperature much colder than usual. But an extended period of very cold weather is more deathly.
  • Sweet potatoes in storage. An ideal crop for winter meals, as they store at room temperature for a long time, maybe seven or eight months.
    Photo Pam Dawling
  • The hardiness map can’t tell you if your plants will survive the summer.  I have had people ask me what zone sweet potatoes can grow in. My reply is that winter-hardiness zones will not affect sweet potatoes, because they are not out there in the soil in the winter! They are in your basement or a root cellar or a storage room, above 55ºF.
  • AHS Heat Zone Map 1997
  • For thinking about summer temperatures, consult the 1997 American Horticultural Society heat zone map that measured the average number of times per year that the temperature of an area exceeds 86ºF. The heat zone map is on the NPR site, if you scroll far enough. With 60-90 days a year with a high temperature above 86ºF, Louisa, VA is in heat zone 7 of the 12 created. I hope an update of this map comes soon.
  • If your winter-hardiness zone has changed, you could plant some new things, or leave plants such as figs, or spinach, that you previously wrapped each winter, unwrapped.
  • Warm microclimates such as containers on paved surfaces or near brick buildings absorb a lot of radiant heat during the day and hold it into the night.
  • Remember the cold-hardiness zone calculations are using the past 30 years’ data. If you notice temperatures are continuing to climb, year after year, you could experiment with less-hardy plants from the half-zone warmer than yours.
  • Your local Extension Service may be able to help with more local information.