Category: Insect pests

Hoophouse Solarization Ponderings

 

Our hoophouse on solarizing day, August 5. Note we kept the big shadecloth over the roof until we had done the work of installing the plastic over the soil. Photo Ken Bezilla

Solarization Benefits We Hope For

I wrote Solarization of Our Whole Hoophouse on 8/12/26. This summer we decided to solarize the whole hoophouse. We hope to reduce fungal diseases in our winter crops, draw down the weed seed bank, and kill lots of nematodes. We planned to solarize for the whole of August (4 weeks). We started that on August 5, and solarized until September 3, a full 4 weeks later.

A One-Month Break from Usual Hoophouse Work

It was a nice break to do nothing in the hoophouse for a month except run the drip irrigation twice a week. We left the drip tape in place so we could water the soil and keep it alive below the hot zone. It was an unearthly sight to just have a sea of plastic in there, and one of the crew popping in there to turn on the irrigation reported that to was quite surreal to walk barefoot on the hot plastic.

We agreed to use the time to do some infrastructure repairs, and did get a new window made and the other one repaired.

We repaired our big all-encompassing shadecloth and reset the grommets to be a better fit with the spacing of the hooks in the baseboards.

We researched horizontal airflow fans to replace our hippy-rigged box fans, but we balked at the $1000 price tag. Maybe EQIP grants would help?

We did our crop planning for the winter and made a map. We cross-checked the schedule against the map and made sure everything fit. We did some perimeter weeding and laid down landscape fabric.

A Bad Choice Narrowly Avoided

We had the notion that if we had thought of it in time, we might have spread mature compost on the beds before spreading the plastic and killed the weed seeds that landed on the compost pile while we ignored it all summer. We got behind with the mowing, and we know grass and spiny amaranth seeded somewhat on to the pile. Fortunately, we didn’t do that! Sterilized compost has most of its microorganisms killed! Instead, we re-composted the weed-seed-infested pile and got a new pile in the meantime.

Hoophouse soil thermometer showing 100F (38C). Photo Ken Bezilla

De-Solarizing Day

On de-solarizing day we allowed a little lead time (not enough!) to disperse some of the 120F (49C) heat by flinging open the doors and windows. The soil temperature was 100F (38C). The peak air temperature during the month may have reached 140F (60C) although no one wanted to linger in there long enough to really study the thermometer. It had been 80F (27C) before we solarized and is back down to that temperature in as I write this in late September.

Normally we leave the big shadecloth in place over the whole hoophouse until mid-September or so, but this year we wanted maximum heating for the solarization, so we removed it a couple of days after solarizing (when it stopped raining).

We had bought 32’x100’ (9.7×30.5m) plastic which was just right for the footprint of our 30’x 96’ (9 x 29m) gothic hoophouse. We unrolled it down the center bed (it was folded in several concertina folds from each edge to the middle). We mimicked that kind of folding to pack it away.

The first step of removing the hoophouse solarizing plastic: folding the edges to the middle. Photo Ken Bezilla

We started by removing the buckets of rocks we had set round the edges to hold the plastic down. Next we folded both sides to meet in the middle. We got old towels to wipe the underside of the plastic dry. We used some of the drying time to teach broadforking and cultivation and raking to new crew members. We noticed how warm the soil was to our hands.

Wiping the solarizing plastic dry between folds. Photo Ken Bezilla

Next we brought the outer folds in to meet in the middle again, and repeated the mopping operation. Later we thought a sponge mop might have been a useful tool. We used more drying time to start to return things we had stored in a shed during Solarization Month.

Removing hoophouse solarizing plastic: second fold of edges to the middle. Photo Ken Bezilla

We repeated the folding until a simple folding in half made a sensible size for rolling, and ended up with a fat roll of plastic tied up with rope. We wrote on it to deter anyone who might think of using that plastic for any other purpose.

The last fold of the the hoophouse solarizing plastic, making it ready to roll once dried. The dried stems are from a buckwheat cover crop we covered with the plastic. Photo Ken Bezilla.

Disadvantages of Solarizing

I was sad to say goodbye to the hoophouse bell peppers as they were the best we’ve had in years. Usually we keep the peppers until October and do our winter crop planning so that the pepper area is the last planted in winter crops, but we made that sacrifice! For several years our peppers didn’t do well, as the salinity of our soil had got too high. We now do salt wash-downs in September and March. This year the peppers were spectacular! Big plants, huge peppers! Rather disappointing to have to pull them at the beginning of August.

Bullnose pepper in our hoophouse June 27. Photo Alexis Yamashita

Several days into the solarizing I realized with dismay that we had killed off all our zipper spiders and probably their egg cases. The spider corpses were still attached to the framework. Zipper spiders seem to be homebodies. Surely they could have found a way to leave? But mostly they do die at the end of summer, just not on open display. In recent years we have not had any of these spiders outdoors, but many in the hoophouse. They do good work consuming the insects they trap.

Zipper spider on the pepper plants in our hoophouse on September 10 a previous year.
Photo Pam Dawling
Zipper spider egg cases hanging from the hoophouse plastic.
Photo Wren Vile

One big disadvantage of our choice was that the work of bed prep and planting in there after de-solarizing was dreadful! We had hot sunny weather, and the allocation of each day’s prep work took 3 hours or more. By lunchtime it was 120F (49C) in there on many days. Exhausting work! But it didn’t seem worth putting the big shadecloth back in place as we normally remove it around September 20.

Hoophouse fall bed prep. Broadforking in plastic sandals is not recommended! Photo Ken Bezilla

Apart from the workers suffering the effects of the heat, the soil also dried out a lot faster, and we had to keep working (no rest!) to break up the big lumps of soil before they became bricks.

We prepped one bed and got ready to sow. We decided to use wire hoops and a 6’ (2m) roll of shadecloth like we do outdoors for lettuce in hot weather. That worked well, although the bed edges did dry out fast, maybe because the paths were still holding heat from the solarizing. So we had to handwater the bed edges daily for a week or so.

Spinach seedlings from pre-sprouted seed in the hoophouse in September.
Photo Pam Dawling

One of the first crops we sow is spinach, using seed pre-sprouted in the fridge for 6 days. No way would it have germinated in that hot hoophouse soil! On sowing day, the spinach seed showed little sign of sprouting, but we sowed, watered well, shaded it, and it came up great! The extra attention paid off. This spinach will feed us all winter until about March, as we just harvest leaves. By September 21, all the early crops in that bed had emerged (scallions, Bulls Blood beets, tatsoi, radishes as well as the spinach). We needed to remove the shadecloth from the bed once everything had emerged, so the seedlings didn’t get leggy. 12 hours of daylight isn’t so much.

The perennial weeds growing in under the baseboards did not die. Once we removed the plastic the wiregrass (Bermuda grass) raced across the edge bed and started colonizing the next bed. Fortunately juvenile wiregrass is relatively easy to pull up.

De-solarizing our hoophouse. Note the vigorous wiregrass along the south baseboard. Photo Ken Bezilla

Most years we grow summer cover crops in the hoophouse, thus keeping the soil-life active and adding organic matter. This summer offered no gain of organic matter, which I do regret.

Advantages of Solarizing

We have sowed an outdoor seedbed with things to transplant into the hoophouse in October when we have more beds prepared. Work is progressing well, although we’ve had to scramble some days to stay on track.  Because using transplants from outdoors is part of our usual plan, we did not have to make any changes to the beds after the first one, om account of high temperatures.

The advantages of solarizing will become apparent in the next 6 months. Two weeks after uncovering the soil we did find a tiny tomato seedling, but the seed could have been dropped from our clothes after the solarizing month, rather than being a survivor. It was interesting to see it.

For myself, I’m unsure if I’d want to do this again. The advantages are going to have to be huge – like no more nematodes. I’ll write more as the next year unfolds.

Solarization of our whole hoophouse

 

Solarization plastic spread across our hoophouse. Next we weighted down the edges with small buckets of rocks. Photo Ken Bezilla

I wrote in August 2019 about Solarization and Crop Choices to Fight Nematodes. Previously we solarized part of a bed in our hoophouse, or one or two beds. I’ve written before about our first efforts at solarization to fight root knot nematodes in our hoophouse. Back then we shoveled soil on the plastic edges to make a good seal between the plastic and the soil. Later we developed a good technique of pushing the plastic edges down into soil using spades, which gives a much better seal, and if you work both sides of the bed at the same time you can avoid wrinkles.

Solarizing a single bed in 2019 using a spade to push the plastic edge into the soil..
Photo Pam Dawling

This summer we decided to solarize the whole hoophouse. We hope to make progress on reducing fungal diseases in our winter crops, drawing down the weed seed bank, and killing lots of nematodes. We plan to solarize for the whole of August (4 weeks). Here’s the story so far.

Solarization

Solarization is a method of killing pests, diseases and weed seeds near the surface of the soil by covering the soil with clear plastic in hot weather. Nematodes are only active in warm weather, and we have not had problems with them outdoors, but of course, it’s warmer in the hoophouse!

In my Book Review: The Organic No-Till Farming Revolution: High Production Methods for Small-Scale Farmers, Andrew Mefferd, I wrote a little about solarizing:

“Solarization uses clear plastic (old hoophouse plastic is ideal). In a summer hoophouse, solarization can be as quick as 24 hours, Andrew says. When we’ve done this, one of our goals was to kill nematodes and fungal diseases, not just weeds, so we waited a few weeks. Outdoors it takes several weeks. You can see when the weeds are dead. Bryan O’Hara poked a thermometer probe through solarization plastic and found a 50F degree (28C) difference between the outside air and the soil immediately under the plastic; a 10F (6C) difference at 1″(2.5 cm) deep and little temperature gain lower than that. Solarization does not kill all the soil life!”

Preparation for Solarizing

Last time we changed the plastic, we saved our old hoophouse plastic in one large sheet, for just this option of solarizing the whole hoophouse. Unfortunately, someone used it for some other purpose, and we ended up having to buy new plastic to carry out our plan. Ouch! Label your old plastic very thoroughly! We bought 4 mil Tufflite Nursery Clear plastic from Nolts Greenhouse Supplies, Ephrata, PA (only rated for one year outdoors), thinner than the 6mil we buy for covering the frame. Be aware that shipping can be a big part of the cost, unless you are ordering lots of things.

Clearing hoophouse tomatoes and sunn hemp cover crop.
Photo Pam Dawling

We pulled up our tomatoes and cucumbers at the end of July, a week earlier than usual. The squash had already gone. I was sad to say goodbye to the bell peppers as they were the best we’ve had in years. Usually we keep the peppers until October and do our winter crop planning so that the pepper area is the last planted in winter crops, but we made that sacrifice! For several years our peppers didn’t do well, as the salinity of our soil had got too high. We now do salt wash-downs in September and March. This year they were spectacular! Big plants, huge peppers!

Lady Bell peppers ripening on 7 July.
Photo Pam Dawling

We decided to keep the big shadecloth in place for the solarizing day, expecting it to be very hot. It wasn’t, but it was a wise precaution. We planned to remove the shadecloth the next day, but it was raining and we need the shadecloth to be dry to pack it away. So we waited a couple of days for our little monsoon season to pass. Normally we leave the shadecloth in place until mid-September or so, but this year we want maximum heating for the solarization.

We are leaving the drip tape in place so we can water the soil and keep it alive below the hot zone. If we had thought of it in time, we might have spread compost on the beds before spreading the plastic and killed the weed seeds that have landed on the compost pile while we ignored it since early April. We were stretched thin and got behind with the mowing, and we know grass and spiny amaranth seeded somewhat on to the pile. We did have it partly covered with a tarp.

Unrolling the Plastic

Unrolling plastic to solarize the hoophouse.
Photo Pam Dawling

We bought plastic 32’x100’ which was just right for the footprint of our 30’x 96’ gothic hoophouse. We unrolled it down the center bed (it was folded in several concertina folds from each edge to the middle). We gradually unpacked the folds and pulled the plastic out to the edges. It is important to get as smooth and tight a fit as possible (few airgaps between soil and plastic).

We designated one person to take their sandals off and walk on top of the plastic, while the rest of us gathered small buckets and put some rocks in them, to anchor the edges. This all went very smoothly and took less time than we expected. We used about one bucket of rocks every 20’ down the length. We rolled our painters’ pole that we use for our SnoBrum in the plastic across the west doorway, the direction the strongest winds come from, for add extra security in preventing wind getting under that edge of the plastic. We did not bury the plastic edges in the soil, as that seemed difficult and we figured a large area would suffer less edge cooling/heat escape than a single bed.

Closing Up the Hoophouse for a Month

We closed the doors and windows and relaxed into enjoying a summer month off from harvesting in the hoophouse. We have made a list of infrastructure repairs, landscape care and, of course, the winter crop planning to do in t he next month. And we’ll be irrigating maybe twice a week and checking the soil thermometer periodically. It showed 80F last week, before we solarized.

Hoophouse solarization at Dripping Springs Garden, Arkansas.
Photo Pam Dawling

More Resources on Solarizing

eOrganic’s Organic Vegetable Production Systems Topics list offers publications on plant disease management, weed management and management of soil-borne pathogens using Anaerobic Soil Disinfestation. Here’s a 2025 webinar about On-farm Anaerobic Soil Disinfestation for the Management of Soilborne Pathogens in High Tunnel Production Systems:

 

https://www.youtube.com/watch?v=2pEf26ae6XI

The University of California Solarization site and their Small and Organic Farm Advisor have good information, including some in Spanish and Hmong

More Resources on Nematodes

I’ve written here before about our struggles with root knot nematodes in our hoophouse, and you can read everything I know about nematodes in the Year-Round Hoophouse.

My article on nematodes in Growing for Market  in November 2014 describes our discovery of the beasties and our first attempts to deal with them. My most thorough blogpost about nematodes was for Mother Earth News  Managing Nematodes in the Hoophouse. It’s free for MEN members.

There is info on dealing with nematodes from Garry Ross in Hawaii, where nematodes are a fact of daily life, in my post Cold weather, snow, thinking about nematodes from February 2015.

Unusual Crop for June: Plant Bug-Resistant Summer Squash Substitutes

Bug-Resistant Summer Squash Substitutes 

Tromboncino Squash. Southern Exposure Seed Exchange

Most summer squash and zucchini are in the species Cucurbita pepo. They are easy to grow —the main challenges are pests, diseases, and moderating the quantities available. These crops can crank out high yields of a vegetable almost everyone likes.

Where insects are a problem for summer squash, vigorous plants of other squash and gourd species can bear all season in those areas. Growers with bad pest problems can try:

  • Tromboncino squash (60d OP), a C moschata squash; Light green fruits grow long, curving to a bell at one end. Vigorous vining plants that can be grown on a trellis. Harvest at 8”-10” (20-25 cm) long when the flavor is fine and sweet. Southern Exposure Seed Exchange. On the coast of France and Italy, Tromboncino d’Albenga and Trompette de Nice were traditionally grown as summer squash and a few fruits left to ripen for winter storage.
  • Zucchino Rampicante (60-70d OP) C moschata; Italian heirloom, vigorous vining squash; long slender 15” (38cm) fruit with a bulb at the bottom. One of the best eating summer squash: very tender, mild tasting. The long neck makes great slices with no seeds in them! Insect and disease resistant. Baker Creek.

    Rampicante squash. Baker Creek
  • Tromboncino and Rampicante are closely related, if not the same.
  • Long de Nice (C moschata); Fruit range in size between 10-20 lbs (4.5-9 kg) each with a long neck and fine-grained flesh with few seeds. Vines spread at last 15ft (4.5m), consider trellising. One or two full-grown squash per vine, but you’ll get more if you harvest them immature. Generally not as long as Rampicante or tromboncino. Baker CreekLong de Nice squash. Baker Creek
  • Luffa (Luffa acutangula and aegyptiaca vegetable sponge, 65d OP, zones 7-13), Very long vines, consider trellising. Tastes similar to summer squash when harvested at 4” (10cm) for eating raw, pickled, cooked with other vegetables. The mature fruits are harvested when the skins dry brown, to use as vegetable bath sponges or pot scrubbers, with an incidental seed harvest at the same time.

    Maturing Luffa. Seed from Survival Garden Seeds
  • Cucuzza (Lagenaria siceraria, snake or serpent gourd, 60-75d OP grows in zones 2a-11b.) Cucuzza edible gourds have more resistance to squash bugs. Just be sure to harvest them relatively small (while skins can be pierced by a fingernail, 12” (30cm) max) for good flavor. These are very vigorous, sprawling plants, which, happily, are also prolific. One option is to plant a row of regular zucchini alternating with these bigger plants —when the zucchini succumb to disease, the sprawlers will take over. Vines can reach 25’ (7.6m)

    Cucuzza Seeds from Italy.
    Growitalian.com
  • Lunga Da Pergola (Lagenaria siceraria, 60d to 6” (15 cm) fruit). Edible gourd, vigorous vines. At its best small, about 6” (15cm) long, when fruits will be slightly sweet and tender. Fruit can grow up to 5’ (1.5 m) long. A very productive strain with white mottling on the gourd and leaves.

    Serpent Gourd Lunga di Pergola. N E Seeds

Some zucchini varieties are especially attractive to cucumber beetles and may be grown as a trap crop: Cocozelle summer squash, Seneca, and Dark Green zucchini. When beetles accumulate in the trap crop, flame it or till it in.

Crop Requirements for Squash and Gourds

Summer squash thrives on high levels of organic matter. Although only a light to moderate feeder for nitrogen and phosphorus, it requires quite high levels of potassium. Foliar seaweed spray can be used to make up for nutrient deficiencies. This crop does best with plentiful, but not excessive, moisture. That said, be careful not to overwater the seeds before they germinate, or they will rot.

This frost-tender warm-weather crop germinates at 60°F (15.5°C) minimum and does best at 85°F (30°C). Germination takes 5–10 days. During growth the ideal temperatures are 75°F–85°F (24°C–30°C) in the day and 65°F (18°C) at night.

Sowing Squash and Gourds

Seed can remain viable for up to 5 years, if stored in a cool, dark, dry place. Seeds should be sown 0.5″–1″ (1–2.5 cm) deep, 6″–12″ (15–30 cm) apart, in widely spaced rows if you are not trellising. Sow deeper in hot weather, when it helps to turn on the drip irrigation, and sow each seed right by an emitter. Water at sowing, then not again until seedlings emerge. For a slightly earlier harvest, you can pre-sprout the seed.

Covering the row with netting will keep the pests away. If possible, use hoops or a rope above the row, pulled taut between stakes, to hold the netting above the leaves, as cucurbits are susceptible to abrasion damage. Remove the netting as soon as you see female flowers, to allow for pollination.

Transplanting Squash and Gourds

When transplanting squash, take care to disturb the roots as little as possible. If you sow 2 seeds in each cell, be sure to pinch off the smaller one as soon as possible to remove the competition.

As soon as the plants have one or two true leaves, at about 3–4 weeks of age, transplant in a mild spell, burying the entire stem below soil level, up to the seed leaves (carefully!) to protect it from damage. Cucurbits started indoors grow long spindly stems, which are quite fragile. Make the hole deep enough, slip the plant out of the container, perhaps on the blade of a knife, pop it into the hole, and close up firmly.

Plant 2’–3′ (60–90 cm) or more apart in the row. Transplanting allows a crop to be established earlier than would be possible with direct sowing in spring. Alternatively, a crop can be gained from a summer window in the planting schedule for a bed, after an early spring crop. Transplants do not grow as sturdy a root system as direct sown squash do, so I would not recommend transplanting if direct sowing is possible.

Pests of Squash

Squash bugs are probably the most common pest. The adults are long gray insects that emerge from overwintering in wooded areas once temperatures reach about 70°F (21°C). They are more attracted to pepo squash than they are to moschatas. Plants attacked by squash bugs look baked to a crisp, with curled bronzed leaves. Squash bugs can do a lot of direct damage to leaves, and they also vector yellow vine disease. They feed on young seedlings for preference and lay groups of spaced bronze eggs on the undersides of leaves. The eggs hatch in 10 days, and the nymphs suck sap from the plants. There are many generations each year, and numbers quickly build. Drop handpicked adults into soapy water rather than crushing them as the smell of the crushed bugs attracts more. It is also possible, but not easy, to crush the hard-shelled eggs. An alternative is to tear off egg-covered leaf pieces and drown the eggs in soapy water. Squash bugs can be trapped overnight under boards on the soil near the plants —in the morning, lift the boards and collect the bugs.

For more info on squash bugs, see the ATTRA publication, Squash Bug and Squash Vine Borer: Organic Controls, that includes pest lifecycles, systems-based management practices, mechanical and physical practices, and biological and botanical controls. Buckwheat can be interplanted to attract tachinid flies that parasitize squash bugs.

Striped cucumber beetles are our worst pests some years, even compared to squash bugs. In the hoophouse, we handpick the adults inside squash flowers in the mornings while they are still sluggish. Long pointed tweezers are our tool of choice. Our hope is that, by battling this first generation, we will reduce numbers for the rest of the season. To attract beneficial insects that are predators or parasites of the cucumber beetle, grow buckwheat, cilantro, dill, or winter peas near the squash plants, timed so that they flower when the rowcover or netting is removed from the squash plants. Another method of reducing pest attacks, especially useful after flowering, is Surround kaolin clay spray. It does need renewing after rain or overhead irrigation. If all else fails and action is imperative, Spinosad will kill them (and some other insects too).

The adult squash vine borer is a fairly large orange-and-black fuzzy moth with glassy black wings. It is active in May and early June, and there may be a second generation in late July/early August. The small flat brown eggs are laid singly at the base of the stem. The larvae hatch after 1 week, and are white with a brown head. They spend 4–6 weeks in the stem, eating upwards and growing to 1″ (2.5 cm) in size. Then they dig into the soil and pupate for the winter.

Plant symptoms include wilting of the whole plant and stem holes surrounded by frass (caterpillar poop). To save the plant, act at the first sign of trouble and pick out the grub, then pile soil over the injury to help the plant recover. Injecting Bt (Bacillus thuringiensis) into the stem is another solution. For prevention, rotate crops and use netting or rowcover over plants until flowering. Another technique to try is pinching out the growing tips of the vine when it is 1’–2′ (30–60 cm) long, which causes the plant to branch and increases the odds that some part of it will survive.

Diseases of Squash and Gourds

I haven’t yet done a Plant Diseases of the Month Series, so I’ll include info here.

  • As always, aim to avoid diseases by ensuring good air flow and appropriate water levels.
  • Powdery mildew (PM) (a white coating starting on older leaves) is a common fungal disease in hot dry weather. Drip irrigation helps reduce the spread of PM, compared to overhead irrigation.
  • Downy mildew (yellow angular spots with leaf curling and a purplish cast to the undersides of leaves) happens in cool wet weather late in the season, and plants can recover if the weather heats up.
  • Anthracnose (dark brown spots on the leaves and round sunken spots on the fruit) is a fungal disease worse in warm wet weather from mid-season onwards.
  • Angular leaf spot, Pseudomonas syringae pv. lachrymans (browning of the leaf between the veins and small round spots on the fruit) is a bacterial disease more common in cool damp weather. The symptoms can resemble those of downy mildew.
  • Black rot/gummy stem blight (Didymella bryoniae) is a fungus occurring with wet soils, in wet weather (cool or warm).
  • Mosaic viruses can be spread by aphids. Succession cropping helps evade these.
  • Bacterial wilt (Erwinia) causes sudden dramatic wilt and death of the whole plant. It is spread by cucumber beetles.

This post is adapted from a chapter in my second edition of Sustainable Market Farming, with some additional information on squash varieties.

Front cover of Second Edition of Sustainable Market Farming book
The second edition of Sustainable Market Farming, release April 15, 2025

Sweet Corn Almanac – it’s planting time!

Young sweet corn plants in July. And solar panels.
Photo Bridget Aleshire

It’s sweet corn planting time for many of us again and many growers are searching my site for information. Here are quick links to my many sweet corn posts over the years. Inevitably there is some overlap. There’s also a full chapter on sweet corn with all this information in my book Sustainable Market Farming, 2nd edition.

After these links there are seasonal details on planting sweet corn.

  • Success with Planting Sweet Corn: Before you plant, understand the 6 sweet corn genotypes and avoid producing starchy unpleasant-flavored corn caused by planting warring types; soil temperature requirements; amount of seed required; seed spacing and depth; an overview of our corn-growing methods; sweet corn crop requirements; dealing with weeds; transplanting sweet corn; my slideshow on Succession Planting.
  • <iframe src=”https://www.slideshare.net/slideshow/embed_code/key/9pRbveAmBcqtaz” width=”510″ height=”420″frameborder=”0″ marginwidth=”0″ marginheight=”0″ scrolling=”no”style=”border: var(–border-1) solid #CCC; border-width:1px; margin-bottom:5px; max-width:100%;”allowfullscreen></iframe><div style=”margin-bottom:5px”><strong><a href=”https://www.slideshare.net/slideshow/succession-planting-for-continuous-vegetable-harvests-2024-60-mins-pdf/280479965″ title=”succession-planting-for-continuous-vegetable-harvests-2024-60-mins-pdf” target=”_blank”>succession-planting-for-continuous-vegetable-harvests-2024-60-mins-pdf</a></strong>from <strong><a href=”https://www.slideshare.net/SustainableMarketFarming” target=”_blank”>Pam Dawling</a></strong></div>
  • Preparing for Sweet Corn: Crop rotations; planning for succession plantings for a continuous supply; planning preceding cover crops for next year; problems with living mulch; under-sowing for a follow-on cover crop; caring for growing sweet corn; staying on top of weeds; sweet corn growth stages.
Sweet corn growth stages. University of Illinois Extension
  • Growing Great Sweet Corn: More on caring for sweet corn as it grows, including resources; under-sowing sweet corn; succession planting, including a link to my slideshow on this topic; last worthwhile sowing date; fast-maturing sweet corn varieties; sweet corn season extension including transplanting; pests and diseases of sweet corn; harvesting sweet corn.
  • Sweet Corn, Potatoes and Okra: includes my slideshow on succession planting, sowing with an EarthWay seeder; using a wheel hoe between corn rows; hoeing sweet corn; our sowing and harvest start dates; dealing with raccoons, skunks and curious cats.
Our first sweet corn of the season. Bodacious
Photo Pam Dawling
Mature Sweet corn ear.

Skunks

When harvesting our fifth planting of sweet corn (Bodacious, Kandy Korn, Sparkler and Silver Queen), I beefed up our raccoon traps following the suggestions from Joanna Reuter of Chert Hollow Farm, staking the traps down and smearing peanut butter high on the stake in the back of the cage. Well, the first morning I caught a small, very white skunk! I let it out carefully. The next morning I caught the same skunk again. And the third morning, again. The little animal never seemed ferocious or scared, more curious about how to get out. I was more scared than it was, I think! I bet you’re wondering how I released it. Well, I gently laid a large plastic bag over the top and nearside of the trap (just in case. . . ) and gingerly unlatched the door. Then  I used a strong stick to lever up the door a bit, as it is a tight fit. Then I bravely put my foot on top of the trap and pulled the door up by hand. Then I dropped the stick and ran! Later the skunk ambled out. By the third morning I think it was happy with the arrangement. A small can of cat food is a big meal for a small skunk, after all. But I was tired of the game, so I took the traps away. Raccoons don’t seem to like Silver Queen as much as Kandy Korn anyway, maybe because the husks are tighter and harder to rip off. Actually I like Kandy Korn better than Silver Queen too! Meanwhile we are working on setting up a temporary electric fence around the last corn patch, with our new solar charger.

A Way to Garden

For a valuable second opinion, see Margaret Roach (who grows in Massachusetts) in A Way to Garden:

Seasonal tips on planting sweet corn

  • Ensure you have compatible sweet corn varieties, and that none of your seed is older than one year.
  • Plan where your corn will go, and calculate how much seed you need.
  • Use a soil thermometer! Flag its location so you don’t lose track of it! Sweet corn needs warm soil. Catalogs usually indicate the soil temperature (measured at 4″ (10 cm) deep at 9am) recommended for each variety. 50°F (10°C) is the absolute minimum, and applies to treated seed and OP or (su) varieties only. 60°F (15.5°C) is better for most, and 65°F (18°C) or higher is required by some varieties.
  • Corn has no tolerance of frost, but escape from a late spring frost is possible if the seedlings are less than two weeks old and not yet very tall, as the growing point may still be underground. Thus, in a spring that promises to be warm and dry, it is possible to risk an early planting as much as 2-3 weeks before the last frost date. Having some transplant plugs for a back-up helps reduce the risk level.
  • Common phenology signs for the season being advanced enough to sow corn are that white oak leaves are the size of squirrels’ ears and that ragweed is germinating.
  • Sow shallowly 6” (15 cm) apart, in rows you’ll be able to walk between. 30”-36” (76-92 cm) works well. Close the furrows and tamp down the rows with the back of a hoe or rake, or do the “soft shoe shuffle” with your feet. The goal is to get good contact between the seed and the soil.
  • Water as needed.
  • Emergence takes 22 days at 50°F (10°C), 12 days at 59°F (15°C), 7 days at 68°F (20°C), and 4 days at 77°F (25°C).
Our first sweet corn harvest of the year. We like to leave the husks in the field, but it does mean they need good washing before cooking. Pam Dawling

Crop protection and support ideas for smaller gardens

Eggplant transplants under a food safe for protection from pests. Pam Dawling

Crop Protection on a Small Scale

I’m more usually writing about large gardens or small farms, and in the case of protecting crops from pests, long rolls of rowcover or netting. But if you have a small number of important plants you could consider using a food safe. These netting structures close like umbrellas for storage, and keep bigger insects out.

The eggplants above have just been moved outdoors after being raised indoors without any netting, when they suffered aphid predation. The food safe fabric wouldn’t keep tiny insects off – it’s like tulle (bridal veiling).  Outdoors it can keep insects and small rodents away, but not whatever creature especially love Swiss chard! This garden had a single chard plant in a bed of tatsoi, pakchoi and Napa cabbage. Those Asian greens stayed protected under the food safes. An exposed row of spring kale was not eaten either. But over a few days Something ate the whole chard plant down to the ground!

Site of the disappeared chard plant. Pam Dawling

The creature ripped through two sides of the food safe (entry and exit?) If you have any idea which creature particularly loves Swiss chard, please leave a comment at the end of this post.

Food safe that failed to save the chard. Pam Dawling
The far side of the ripped food safe. Pam Dawling

Crop Support on a Fairly Small Scale

Raspberry Trellis suiting for fall fruiting. Pam Dawling

In the same garden is this trellis for restraining raspberries in a way that can be easily dismantled to mow for fall fruiting. Fall raspberries fruit on the primocanes, the ones that grow that spring. There are particular varieties developed for fall fruiting, and some that can be used either for summer or fall fruiting, depending how you prune them. They are a great way to extend the fruit season, and their pruning is simplicity itself! Roll up the cords or wires. Mow the canes down after fruiting, and weed. In early spring, thin the canes to 2″ apart, install and tension the wires or cords between the posts.

The same system can be used for summer raspberries, but you’ll have to deal with the wires while pruning, as in other trellis systems.

This trellis uses 4″ x 4″ posts with crosspieces at 1.5′, 3′ and 5′. They have holes drilled towards the ends and paracord threaded through.

Raspberry trellis with paracord threaded through the arms and tied at one end. Pam Dawling

At the far end the cords are tensioned using plastic “camjam” cord tighteners. You could alternatively just pull and tie them off for the season. On a larger scale using wire you could use something from the fencing supplies.

Raspberry trellis paracord tensioned with cam locks. Pam Dawling

Pests of the Month in April: Garlic bloat nematodes

Garlic bulb cut horizontally to test maturity (almost!)
Photo Wren Vile

This is the last of my monthly series on pests. Scroll down for links to the others and to each of my ten monthly series.

I’ll start with a few seasonal tips, then get to details of the garlic bloat nematode

  • Aphids, see Posts in February and November
  • Cabbage moths, see my December post. In mid-April we finish filling gaps in broccoli & cabbage plot, and plant alyssum every 6 ft in center of beds. Alyssum is a wonderful flower for attracting beneficial insects. Link to Good Seed Co. post on decoy butterflies: https://goodseedco.net/blog/posts/cabbage-butterfly-decoy. Encourage paper wasps, they will haul away lots of caterpillars! Use Bt against caterpillars. The Action Threshold is an average of 1 cabbage looper, 1.5 imported cabbageworms, 3 army worms or 5 diamondback moth larvae per 10 brassica plants.
  • Keep eggplant above 55°F and netted against flea beetles.
  • Colorado Potato Beetles Deal with potato beetles with Spinosad [or Neem] once larvae are seen, if >50 adults/50 plants or >200 larvae/100 plants. Spinosad: Shake well, 1-4 Tbsp/gall (1fl.oz=2Tbsp=30ml.) Repeat in 6 days. See this June post on monitoring for CPB. Also see this post on potato pests and diseases from June 2020

Special Topic for April:

Garlic Pest Field Notebook. University of Maine Cooperative Extension, 2022

Garlic stem and bulb (bloat) nematode (Ditylenchus dipsaci)

As garlic is growing, be on the alert for bloat nematodes. Anytime your garlic grows poorly and you can’t tell why, send a sample with the soil it’s growing in to your Extension Service to be tested for nematodes. Symptoms of garlic bloat nematode are similar to some other pathogenic organisms, such as bulb mites or Fusarium, so get an accurate diagnosis and take the appropriate management steps.

Nematode infestations show up as stunted, distorted, bloated, spongy leaves and bulbs, perhaps with brown or yellow spots. Cloves may turn soft and brown. Top growth yellows and dies prematurely and may separate from the root system. Pull up a suspicious plant and the roots may stay in the ground. Cracking may be seen around the basal plate later in the season. Infested bulbs are light in weight, shriveled, soft and brown.

Large numbers of nematodes (microscopic worms) can congregate as a visible woolly mass between wrapper layers. Weakened plants are more vulnerable to other pests and diseases. These nematodes can overwinter in the soil and can attack any allium, as well as other bulbs, celery, parsley, nightshades, and some varieties of peas and lettuce. Even low populations (less than 10 nematodes per 0.5 quart/liter of soil) have been recorded as causing significant crop loss.

Garlic infested with bloat nematodes. Eric Sideman

The lifecycle can take as little as 3 weeks in favorable conditions – this pest is favored in cool damp conditions. The eggs hatch in the soil, and when the soil is damp, the fourth and final juvenile stages swim to the surface and enter the garlic through wounds, leaf axils and even stomata. Nematodes at this stage can survive years in dead plant matter. The final molt occurs inside the plant tissue, and the adults emerge to reproduce. An adult female nematode can lay 500 eggs.

The problem is usually spread by infested seed, so if you suspect nematodes, carefully do the hot water pre-plant seed treatment in future. See Pre-plant seed garlic treatments against diseases and pests (including garlic bloat nematode)

Garlic bloat nematode infestation. UMass Extension Vegetable Fact Sheet

Destroy known infested bulbs (don’t make a cull pile that can spread the nematodes through rain runoff later – they move in a film of water). Do not replant any cloves, even from bulbs with no visible symptoms, if there was any infestation in the crop. Nematodes can survive winter and very dry conditions, in the plant or free in the soil.

Use a 4-year rotation away from all susceptible crops. Practice very careful sanitation and consider biofumigation with mustard or sorghum-sudan cover crops ahead of the garlic planting season. Be careful not to move infested soil to clean areas: this is the main way of spreading infestation (other than introducing infested cloves). Nematodes cannot move far under their own steam.

Garlic beds in April. Keep them healthy! Photo Kathryn Simmons

 

Resources on garlic and bloat nematodes

eOrganic Insect management in Organic Farming Systems has a long list of dozens of short publications, including specific ones for nematodes, as well as scouting and farmscaping.

ATTRA Organic Production of Garlic, Onions, and Other Alliums includes the use of tarping, solarization and anaerobic soil disinfestation as ways to reduce pest problems next year, and about pests such leaf miners.

Bloat Nematode on Garlic. Cornell University College of Agriculture and Life Sciences, 2015. https://rvpadmin.cce.cornell.edu/uploads/doc_325.pdf

Garlic Seed Foundation.

Grey Duck Garlic. The Complete and Easy Guide to Growing Gorgeous Giant Garlic from Seed. greyduckgarlic.com

Johnson, S. B., & Fuller, D. Garlic Pest Field Notebook. University of Maine Cooperative Extension, 2022. extension.umaine.edu/agriculture/wp-content/uploads/sites/14/2022/02/Garlic-Field-Guide-updated-02.22.pdf

Madeiras, Angela. Garlic Bloat Nematode. UMass Extension Vegetable Fact Sheet, 2015.

Poromarto, S. H., et al. Decrease in Population of Ditylenchus dipsaci in Garlic Cultivation with the Application of Mycorrhizae and Organic Fertilizers. IOP Conference Series: Earth and Environmental Science, 1114(1), 012062, 2022. https://iopscience.iop.org/article/10.1088/1755-1315/1114/1/012062

Sideman, E. Garlic Bloat Nematode. Maine Organic Farmers and Gardeners, 2012. mofga.org/resources/garlic/garlic-bloat-nematode/

 

Round up of Pests every Month of the year:

  • May Cucumber beetles and squash bugs
  • June Mexican bean beetles and harlequin bugs and tips on many more seasonal pests
  • July Corn earworm, cutworm and tomato hornworms
  • August Grasshoppers, brown marmorated stink bugs, and Japanese beetles, with tips on harlequin bugs, cutworms and spider mites
  • September Brassica caterpillars, blister beetles and allium leaf miners
  • October Squash bugs, squash vine borers, spinach webworms, squirrels and groundhogs
  • November Aphids and slugs
  • December A mystery cocoon, buck moth, various brassica caterpillars, beet webworms, grasshoppers and crickets.
  • January Vegetable weevil larvae in the hoophouse
  • February Oils and soaps for aphid control
  • March Allium leaf miners and asparagus beetles
  • April (this one!)

Summary of my monthly series

 My next monthly series

Unusual crops for the month – leave a comment with your ideas.

Pests of the Month in March – Allium Leaf Miners and Asparagus Beetles

Allium leafminer pupae on bulb onion. Photo by Debbie Roos.

Here’s another post in my monthly series on pests. I feature the pests I’m most familiar with here in central Virginia. If you are in a different climate, you can use the Search Box on this site. All the crop chapters in the new second edition of Sustainable Market Farming also have sections about dealing ecologically with pests. If you have other good strategies, please leave a comment on this post.

Pests in February covered how to remove aphids with insecticidal soap.

Pests in January covered vegetable weevil larvae, a hoophouse winter greens problem here.

Pests in December featured a mystery cocoon, the buck moth, various brassica caterpillars, the beet webworm, grasshoppers and crickets.

Pests in November covered aphids and slugs

Allium leaf miners

Here’s information from my book Sustainable Market Farming, 2nd edition (2025):

Allium leaf miners (Phytomyza gymnostoma) are invasive pests attacking all allium types in the South, feeding on the sap. Penn State Extension has some good information on them. The adult form is a small (0.13”/3 mm) long-winged black fly with distinctive orange patches on the head. The female emerges from the soil in spring and makes slits as a straight line of white dots in the leaves, depositing eggs.

The yellow larvae are about 0.3″ (8 mm) long, and drill down towards the bulb. Weakened plants are prone to fungal and bacterial infections. The pupae, mahogany cases the size of a rice grain, are found all summer under the outer skin of the bulb or neck of the plant. A second generation emerges in the fall, and pupae overwinter in the soil. There is no cure.

Allium leaf miners can be a problem here in central Virginia in March/April and Sept/Oct. Covering alliums with hooped rowcover or very small-mesh netting tightly fastened down to the soil, during the periods while the miners are flying, can keep them out.

Follow stringent crop rotations, use preceding brassica cover crops, avoid excess nitrogen fertilizer, do very good postharvest cleanup. Soil solarization works well to deal with a heavy infestation.

Examples of oviposition marks left on allium leaves. The far right photo also shows mining by an allium leafminer larva. Photos by Debbie Roos.

Debbie Roos reported on Growing Small Farms in spring 2024, that some growers in the North Carolina Piedmont noticed new problems with their allium crops, especially bulb onions, leeks, and garlic.

Allium leafminer was first detected in the northeastern U.S. in 2015, and in North Carolina in 2023.

Symptoms include twisted/distorted leaves, stunted plants, and even plant death. Below ground, brown pupae infest the plants and larvae feed inside the leaves and bulbs.The crop damage may be small (rows of oviposition dots on the leaves, that also feed exudate to the flies), medium (twisted leaves on leeks and scallions, worst in the fall), or terrible (rotted leaves and bulbs infested with yellow-white larvae and pupae resembling mahogany-colored rice grains or sesame seeds.)

Debbie Roos maintains a web page with photos and lots of information. The most recent update is February 2026! Early spring is the time to be on the lookout for the allium leafminer, as flies could start emerging in NC as early as February, (they start laying eggs in March in New York). Her web page discusses control strategies. Her January 2025 post Growers: Start Scouting in February for the Allium Leafminer has excellent photos plus control strategies.

Dead allium leafminer fly found inside a garlic bulb. The allium leafminer fly is only 1/10″ long and has a mostly yellow/orange head. Photo by Debbie Roos.

Allium Leaf Miner in Virginia

We found this pest in 2025 in our leeks in Virginia, and I wrote a post in September 2025 that included allium leaf miners.

I had a comment on that post from someone who netted her leeks and had great success with that. She said she let the weeds get bad because it seemed like a hassle to “unwrap” them to weed. Even so, she got a much better crop than in recent years without netting.

We tried netting in 2025, but a worker removed it, thinking it was squashing the leeks. Our hoops are too small for a full bed (4 rows) of our leeks. We could use two sets of hoops with each set covering two rows of leeks, offset. With one roll of netting over the whole lot. We could get bigger hoops. Johnny’s sells some square hoops 32″ wide x 22″ high.

Photos on Growing Small Farms shows netting successfully draped over bulb onion beds with no hoops.

Crop covers are the most effective control for allium leafminer. They must be deployed before egg-laying begins. Photo by Debbie Roos.

For More Information

ATTRA Organic Production of Garlic, Onions, and Other Alliums to learn about use of tarping, solarization and anaerobic soil disinfestation as ways to reduce pest problems next year, and about pests such leaf miners.

ATTRA Leaf Miners—Botanical Control Formulations for recipes for homemade leaf miner pesticides using Quassia, chili peppers, walnut leaves or neem.

A New Pest for the New Year in Western New York: Allium Leafminer Is Here to Stay – Cornell University

Allium Leafminer Identification, Biology, and Control – Cornell University

Vegetable Blog: 2024 Spring ALM Update – Cornell University

https://onvegetables.com/2018/04/19/new-allium-pest-of-concern-allium-leaf-miner/

https://gardenerspath.com/how-to/disease-and-pests/allium-leaf-miners/

Asparagus Beetles

Common Asparagus Beetle. University of Minnesota Extension
Spotted Asparagus Beetle. University of Minnesota Extension Service

Adult asparagus beetles overwinter in crop debris and soil, emerging in central Virginia in April to lay eggs on the spears. Depending on your climate, March may be time to start scouting. Certainly it’s a good time to tidy up your asparagus patch in preparation for the harvest season.

Asparagus has very few pests, but the two species of asparagus beetle are to be taken seriously. Adults of the Common Asparagus Beetle (Crioceris asparagi) are 0.25″ (6 mm) long, slender, and metallic blue-black with wing covers each having 3 or 4 yellow-white square spots and reddish margins. The thorax is red and usually marked with two black spots. The Spotted Asparagus Beetle (Crioceris duodecimpunctata) is more common in the West and mainly feeds on berries on female plants, so it is less of a problem on the all-male hybrids. The adult Spotted Asparagus Beetle is orange with 12 spots on its wing covers and is slightly larger than the Common Asparagus Beetle at about 0.3″ (8 mm) long. I have seen a few in Virginia.

Eggs of both species are shiny black rods 0.1″ (3 mm) long (about the size of a hyphen), attached by one end to the asparagus spears, giving a bristly appearance to badly infested plants. The eggs are harmless and can be removed after harvest by spraying with water, tub-washing, or wiping.

Asparagus spear with beetle eggs (enhanced). Kathryn Simmons

The eggs hatch after 1 week. Larvae of both beetles are olive-green to dark gray with black heads and legs, becoming plump and humpbacked larvae as they develop, about 0.3″ (8 mm) long. They join the adults feeding on the spears (causing deformed hooked spears) and ferns (reducing the strength of the plants and their ability to photosynthesize).

Larvae mature through 4 instars (over about 8 days) then enter the soil and pupate, emerging as adult beetles in 5–10 days. Later in the season, these new adults lay another generation of eggs. In Virginia, there are two generations per year; in warmer climates, there are as many as five.

Asparagus beetle larvae. University of Minnesota Extension

Good descriptions of both asparagus beetles, along with detailed photos of all life stages can be found on the University of Minnesota Extension page.

 

Biological Integrated Pest Management advocates for a systematic approach to pests, starting with controls that do least damage to other life-forms. The goal is to reduce pest damage to an economically viable level, while minimizing the damage to the environment.

Monitoring, scouting for asparagus beetles once a week from the beginning of the harvest period (that’s early April for us), is the next step. Inspect 15–20 crowns at 4 different parts of the patch. Creep up on them — they drop to the ground if they sense a threat. During the harvest period, the action level is 5–10 adults/100 crowns or 2% of spears infested with eggs. Postharvest period, the action level is 5–10 adults/10 crowns. If control measures are not taken when the infestation is above these action thresholds, permanent damage to the plants will occur.

Control measures, if needed, can start with cultural controls, i.e., management strategies that do not add any new materials. Harvesting all spears taller than 7″ (18 cm) every day removes all the eggs, and hence breaks the life cycle. Asparagus beetles are a threat mostly in the first 6 weeks of harvest. By harvesting for more than 6 weeks, you are gaining control. A practice of culling unsaleable spears can significantly reduce the population.

Asparagus spear damaged by beetle feeding. Kathryn Simmons

Biocontrol options include encouraging or introducing beneficial predators or parasites. Birds may eat asparagus beetles and larvae for the extra protein, which appear conveniently during nesting season. Ladybeetles, lacewings, and a chalcid wasp are predators of the eggs; ladybugs and lacewings also eat the young larvae.

Encourage ladybeetles or consider planting an insectary flower strip in your asparagus patch, to attract ladybugs (see the ATTRA publication: Farmscaping to Enhance Biological Control, by R. Dufour). Flowers that attract beneficial insects include yarrow, phacelia, alyssum, and borage. Planting tall sunflowers in the rows can encourage predators to eat pests, add visual interest, and mark progress when you are harvesting. It’s easy to pop a sunflower seed in the soil alongside every 10th asparagus plant or so.

As a last resort, if the preceding methods have not reduced beetle populations below the action level, use botanical insecticides. The daily harvest makes treatment difficult because few want to spray anything close to harvest time. Insecticidal soap may be effective against larvae. Grandevo CG is a bacterium with spent fermentation media, OMRI listed against asparagus beetles. Spraying in the afternoon is recommended as that is when the beetles are most active. It also allows time before the next morning harvest. Spinosad, also OMRI listed, is a naturally occurring bacillus derived from a soil bacterium. It is not toxic to most beneficial insects but does kill bees, and some fish, birds, and mammals.

An early fall frost caught these asparagus ferns. Photo Twin Oaks Community

Which Organic insecticides work for which pests?

VABF Conference logo

At the Virginia Association for Biological Farming conference a couple of weeks ago, I attended a lot of useful workshops. Dr Tom Kuhar, Professor and Vegetable Entomology Specialist at Virginia Tech, talked about which OMRI-approved insecticides actually work for which pests. Organic methods are more interesting to him, as they require more understanding of insects. Assume any errors here are made by me, not Tom Kuhar.

Tom Kuhar

Try non-chemical control options first

Dr Kuhar started by reminding us to try non-chemical control options first: resistant variety selection, cultural control (agronomic strategies, like changing planting dates, crop rotation), physical control (exclude the pests with netting, rowcover, kaolin clay etc), biological control (predators and parasites).

Chemical control (synthetic substances) should be the last resort (because of collateral damage). Organic insecticides have some limitations and problems: they are usually short-lived, and require frequent applications; they require attention to getting complete plant coverage and sometimes precise timing; they have no systemic activity and often a short shelf life; they may be expensive and, lastly, there is not always good information about their efficacy (and false myths abound!)

Soft-bodied insects

Diatomaceous Earth is a crushed rock that is abrasive to crawling insects and absorbs liquids, drying them out. It doesn’t work on fungus gnats or moths. Be careful handling diatomaceous earth, wear a good dust mask, as it can damage lungs. It also dries out your skin if handled without gloves. It only works on contact, so if it gets washed away by rain, it no longer works!

Terrible aphid infestation and one ladybug larva, on southern peas. Photo Southern Exposure Seed Exchange

Pesticidal oils smother eggs and nymphs of mites and scale insects and are effective on other soft-bodied insects like aphids, thrips, whiteflies and psyllids.  They generally provide longer control than soaps, and like soaps, they can cause phytotoxicity. Read the ingredients, some are plant-based, some fish oil based, others are petroleum products. Look for the OMRI symbol. Trilogy is a 70% extract of neem oil.

Pesticidal Soaps such as M-Pede, DES-X, Safer brands and Concern are potassium or ammonium salts of fatty acids. They provide short-term partial control of aphids, mealybugs, whiteflies, mites and other soft-bodied insects. It is necessary to get very good plant coverage, hopefully insect coverage. The soap disrupts the cuticle of the insect. It doesn’t work on hard-bodied insects, despite the pictures of a grasshopper and a harlequin bug on the Safer jug. At high temperatures soaps can cause phytotoxicity (damage to the plant tissues).

Deer can be deterred by insecticidal soap!

Newly planted sweet potato slips with a motion sensor sprinkler to keep deer away.
Photo Pam Dawling

A surprise for many of us is that insecticidal soaps can deter deer for a week or two, even after one rain! With a big patch of corn, it can work to spray just a border around the corn – you’ll have to experiment (and let the rest of know), with how wide of a border for what size of corn patch.

Botanical Extracts

Next are botanical extracts, essential oils of rosemary, peppermint, clove, cinnamon, and citrus peel. They work as antifeedants or repellents short-term and give fair-to-good action against spider mites. If with adjuvants (often soaps or oils as spreader-stickers) they can be effective on aphids.

Neem extracts are oils, soaps and other extracts containing azadirachtin. They are made from seeds of the tropical neem tree, and work by interfering with insect molting. Hence they are most effective on young insect stages.

Pyrethrins and combos

Pyrethrins are made from dried flowers of pyrethrum daisies. It is a contact poison providing a good, but very short-lived knockdown for a lot of different pests. Not usually worth buying because sunlight and insects break it down quickly.

Striped cucumber beetle in a squash flower. Photo Pam Dawling

Azera is a combination of pyrethrum and azadirachtin (Neem) that is more effective than pyrethrum alone against leafhoppers, cucumber beetles, aphids and caterpillars. Azera is no longer on the market, but apparently you can mix your own (I haven’t got a recipe).

Spinosad (Entrust) is a fermented product of a tropical soil microorganism. It is very effective against caterpillars, fly larvae, thrips and Colorado potato beetle larvae. It can provide fair-good control of flea beetles and Mexican bean beetles. It does not provide good control of aphids, whiteflies, leafhoppers, true bugs or other sucking insects. Use spinosad for listed insects if soaps have not worked. There is a (low) limit on how often you should spray spinosad on the same area.

Trials on 22 different crop/pest combinations

Dr. Galen Dively, Professor Emeritus of the University of Maryland has conducted over 186 trials on 22 different crop/pest combinations. His teams have evaluated the efficacy, rates and timings of registered and experimental organic insecticides. You can read his work on ResearchGate.

Trials comparing the efficacy of Azera, Entrust, Pyganic and Neemix

For flea beetles, Azera, Pyganic and Entrust are more effective than Neemix.

For cucumber beetles, Azera, Neemix and Pyganic were more effective than Entrust (spinosad).

Colorado potato beetle on an eggplant leaf. Photo Pam Dawling

For Colorado potato beetles, Entrust was most effective, Azera and Neemix were more effective than Pyganic.

For imported cabbage worm, Entrust worked best, then Azera, followed by Pyganic, with Neemix last of the four.

For potato leafhopper, Azera and Pyganic were the most effective, but not Neemix, or Entrust.

For thrips on tomatoes, Entrust worked best at reducing the number of thrips per 5 leaves in June, but the percentage of thrips-damaged fruit at harvest was least when Azadirachtin was used. The other pesticides used in this trial were Ecotec (essential oils) and Pyganic.

For thrips on onion, cutflower and tomato in a different trial, Entrust worked best (but not grreat), with Azera, Neemix and Entrust at similar slightly lower levels.

Corn Earworm larvae come in many different colors. And they can bite!
(Photo: J. Obermeyer Purdue Extension)

For corn earworm, Entrust was by far the best (7% damaged ears), but was used in the trial at a not-allowed rate of 8 sprays, while Neemix, Pyganic and the untreated control plants all suffered 91.5-94.5 percent damaged ears. Trichogramma wasps can be effective. Gemstar (a virus) works very well.

Another study compared Efficacy of Common Active Ingredients in Organic Insecticides Against Difficult to Control Insect Pests. Corn earworm has developed resistance to Bt, because of the GMO corn. Bt  of both the kurstaki and aizawai strains did little against corn earworm, even after 7 sprays. Bt has a short shelf life unless refrigerated. It requires ingestion by a susceptible insect to be effective, and breaks down in sunlight.

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

Grandevo (Chromobacterium substugae), Venerate and Majestene (Burkholderia spp) are bacteria-derived insecticides that must be ingested to kill sucking insects, mites, flies and some chewing insects. So far, field trials have not shown good results on hard-to-kill insects. Grandevo does cut the number of lygus bugs by half. Majestene has been shown to reduce root knot nematode galls on tomatoes, and wireworms in potatoes.

Beauveria bassiana fungal insecticide works well on small Cpb larvae, but not wireworms.

For nightshade flea beetle, Azera, Entrust, Seican (a fungicide, insecticide, and miticide derived from cinnamon), TetraCURB Max (Miticide, Insecticide & Repellent made from castor oil, rosemary oil, clove oil and peppermint oil), PFR-97® 20% WDG (a fungus contact insecticide), and BoteGHA ES (Beauveria) all work. PFR and Seican are not labeled for use against flea beetles.

Harlequin bug nymphs (a type of stink bug) on spider flower (Cleome); note, white flecks in the leaf typical of feeding by true bugs. Credit Missouri Botanical Garden

Stink bugs are among the hardest for Organic growers to kill. Ten organic pesticides have been tried without success. Surround (kaolin) does work, giving 50% less insect damage. Kaolin is a clay powder to mix with water and coat the plants to prevent insect attack. It washes off with rain and then must be reapplied. It needs careful washing to remove it from produce before sale. Sprayers must be carefully cleaned and some gaskets may get ruined by the powder. Kaolin also works against plum curculio, caterpillars, aphids on fruit, mites and leafhoppers.

We buy our pest management products (and cover crop seeds) from Seven Springs Farm Supply, in Floyd, Virginia

Pests of the Month in January– Vegetable Weevil Larvae in the hoophouse

Mystery cocoon (not chrysalis!) on Tokyo bekana in our Virginia hoophouse in November. Photo Pam Dawling

Pests in December started with a “Mystery Chrysalis,” and confidently claimed I now knew the difference between a chrysalis and a cocoon. Well! I sent the photo to our Virginia Entomology department and they told me it is a cocoon, not a chrysalis! And indeed, now I know, it is plain to see that this structure is spun fibers, and therefore a cocoon. The shape is not typical of the long oval cocoons I have seen previously. The entomologists told me they thought it was some kind of parasitic wasp. I rushed back to see if I could collect it and save it until the creature hatched out. But I was too late. Something had either already left, or died in the attempt.

My monthly series on pests 

I feature the pests I’m most familiar with here in central Virginia. If you are in a different climate, you can use the Search Box on this site. All the crop chapters in the new second edition of Sustainable Market Farming also have sections about dealing ecologically with pests. If you have other good strategies, please leave a comment on this post.

Pests in October discussed squash bugs, squash vine borers, spinach webworms, squirrels and groundhogs (not insects!)

Insect Pests in September discussed brassica caterpillars, blister beetles and allium leaf miners.

Incidentally, while searching online for a picture of the vegetable weevil larva, I found that many of the images were pure fiction, generated by AI. When my cursor hovered over the bottom left corner of an image I saw the admission. This meant I had twice as many pages to trawl through as I would have if I’d known and had filtered for NO AI. I recommend searching directly in BugGuide.Net or Bugwood Images.

Vegetable Weevil Larvae

Vegetable Weevil. Pest and Diseases Image Library , Bugwood.org

This month I’ll focus on a pest that is a particular trouble in our hoophouse and greenhouse in January: the vegetable weevil larva. Both the larvae and the adults feed on leaves and roots of chosen plants at night, hiding during the day. They eat a wide range of plants: brassicas, tomatoes, potatoes, carrots, beets, beans, many weeds and some ornamentals. They especially like turnips, pak choy and the flavorful mustardy greens.

Vegetable Weevil larva, Debbie Roos, N.C. Cooperative Extension, Chatham County Center

Virginia Tech has a two page Description and Biology of the Vegetable Weevil

This pest, Listroderes difficilis Germain is native to South America and is now found in southern and western parts of the US. The adults are gray-brown 6-8mm (1/4-1/3 inch) splotchy bristly snouted creatures. Newly hatched larvae are slender pale c-shaped grubs with darker heads. Mature larvae are about 14 mm (0.6 inch) long and are chubby whitish grubs with pale brown heads.

Damage by vegetable weevils of Listroderes spp. John C. French Sr., Retired, Universities:Auburn, GA, Clemson and U of MO, Bugwood.org (The light in this picture is a bit purple.)

They live in the soil and stay underground or deep in the heart of the plants during the day, so if your leaves are holey, but you can’t find any culprits, or even any frass (insect poop) you can suspect vegetable weevil larvae. Close inspection of the plants may reveal small larvae in the crown of the plant, at the base of the leaves. Often I don’t see any. The feeding holes start as small round holes, but can grow to irregular shapes, and leaves can even become skeletonized. Young plants can be killed by stem girdling.

Stem girdling damage by Vegetable Weevil. Ronald Smith, Auburn University, Bugwood.org

Lifecycle of the Vegetable Weevil

There is only one generation of vegetable weevils each year and adult weevils live 1-2 years.

No known male vegetable weevils exist. The females are parthenogenetic (reproducing young from unfertilized eggs). They lay eggs near the soil line of the plants in late summer, and sometimes early spring. Eggs and larvae develop slowly and the mature larvae pupate underground in the winter, with adults emerging the following spring.

Adult weevils have been known to feign death when disturbed, even dropping off the host plant.

Adults aestivate (it’s the opposite of hibernate) during the summer. They don’t fly much, and so undisturbed crop debris at the field edges is a good off-season location for them. Remember to mow!

Vegetable weevil larvae hiding in bok choi leaves. Debbie Roos, N.C. Cooperative Extension, Chatham County Center

Biological Management of the Vegetable Weevil

Removing crop debris can reduce their numbers. Crop rotation away from susceptible hosts is helpful, as is soil cultivation and tilling after crop harvest.

Natural enemies include ground beetles and rove beetles which search for prey at night. Plant insectary flowers and create habitat to encourage generalist predatory insects.

We have successfully used Spinosad against them. We sprayed with Spinosad on a Monday, then again on Friday, and the next Monday and Tuesday I couldn’t see any new holes.

Neem oil and pyrethrins are other organic control options. Insecticidal soap can be used against the larvae.

Debbie Roos of Growing Small Farms wrote about this pest in “The Bok Choi Problem” which has very good photos.

Resources

Also see resources in earlier Pest of the Month posts

ATTRA, Farmscaping to Enhance Biological Control. 2000. Rex Dufour.

ATTRA, Biointensive Integrated Pest Management. 2001. Rex Dufour

eOrganic Biological Control of Insect Pests Mary Barbercheck, Penn State University

eOrganic Biological Control Options in Vegetable Production  webinar

Organic Pest Management. Debbie Roos, NC State Extension: Growing Small Farms. Photos of beneficial insects.

Insect Pests in December: Wildlife in our Hoophouse

 

Mystery chrysalis on Tokyo bekana in our Virginia hoophouse in November. Photo Pam Dawling

Mystery Chrysalis

Last week (November 18) I found this chrysalis attached to the center of a Tokyo bekana plant. I don’t yet know what it is. If you know, please leave a comment at the end of the post.

I did learn the difference between a chrysalis and a cocoon. In case you, too, are confused, a chrysalis is the quiescent insect pupa of a butterfly. The pupa is the stage between a larva (caterpillar) and an adult. The chrysalis is a tough-ish, smooth, hardened skin of the butterfly pupa, made from shed skin cells of the caterpillar, and its own exoskeleton. Only butterfly species make a chrysalis. When fully grown, the caterpillar makes some silk to fasten its body to a leaf or a twig. This may be a sling, as in Swallowtail butterflies, or a simple attachment and suspension rod as in Monarchs. Next, hanging down from the attachment point, the caterpillar sheds its skin for the final time, and under the old skin is the thicker-skinned chrysalis. When the pupa transforms into the adult it sheds the chrysalis, to make its way out. Most internet searches seem to focus on Monarch chrysalises/chrysalides, which are definitely very beautiful, but not what I was looking at.

Moths make only cocoons. Some other creatures, such as mud dauber wasps, also make cocoons. Moth caterpillars spin a cocoon from silk and wrap it around themselves while they transform via the pupal stage into adult moths. Cocoons are soft, fibrous and usually tan or beige in color.

Buck Moth (Hemileuca maia), aka saturn moth

In October I found a group of buck moths in one corner of our hoophouse. These were new to me and I spent a bit of time identifying them. At first, websites were telling me they were rare, but I soon found out this is not so. Most of our moths flew into webs of the zipper spiders (garden spiders) and ended their days feeding the spiders. Buck moth caterpillars feed on oak leaves and other host plants, but rarely cause much damage to the hosts. Their caterpillars have venomous stinging spines. There is one generation each year. The eggs are laid in the fall, and overwinter and hatch in the spring.

If you get stung by one of these caterpillars, immediately wash the affected area to remove any lingering hairs and venom. An icepack will reduce the swelling, but discomfort may remain painful for a few days.

Imported Cabbage Worm (Pieris rapae), aka imported cabbage white butterfly

Lifecycle of the Imported cabbage worm. Clockwise from top left: adult butterfly, egg, caterpillar, chrysalis. Utah State University

Among our luxuriant Tokyo bekana plants I found all too many of these velvety green caterpillars, feasting on our greens and leaving lots of frass. Numbers are low enough that we can probably hand pick them. The imported cabbage worm is the offspring of the cabbage white butterfly, and you may be able to fend them off by making decoy butterflies. They are territorial and will avoid crowding in one spot. Here’s the link to a template: http://goodseedco.net/blog/posts/cabbage-butterfly-decoy

There are several cabbage caterpillar pests and although they can all be dealt with in the same ways, it’s good to know what you are up against.

Four types of caterpillars that feed on brassicas. Clockwise from top left Imported cabbage worm, cabbage looper, diamondback moth, cross-striped cabbageworm.

Another caterpillar pest of brassicas is the cross-striped cabbageworm (Evergestis rimosalis).  I was quite surprised to see that the adult moth looks so different from the butterfly of the imported cabbage worm. As a child I was told they looked similar. Not so!

Another is the diamondback moth, (Mamestra brassicae). This one also feeds on tomatoes and sunflowers.

Here’s a link to info on the cabbage looper, (Trichoplusia ni), which is pale green with side stripes of yellowy-green.

Beet Webworm (Spoladea recurvalis)

Adult spinach/beet webworm (Mark Dreiling,
Bugwood.org).

We found quite large numbers of this moth (also known as spinach webworm) on our hoophouse senposai last November. As described by Virginia Tech Extension, the adult moths are typically active in late summer. The caterpillars feed on spinach, beets, Swiss chard and amaranth (including pigweeds and lambsquarters).

There’s a nice source of information on Insectidentification.org

Grasshoppers (Melanoplus spp.) and Crickets (Gryllus spp.)

There are still a few grasshoppers in our hoophouse, but the numbers are not damaging. The ones I’m seeing now are Differential Grasshoppers (Melanoplus differentialis, the ones with chevron marks on their thighs), which eat plants. We also have some Field Crickets. Crickets eat plants, especially seeds and fruits, but also insects.

Biointensive Integrated Pest Management

I have written in another post about biointensive IPM, which is a series of steps to manage pests, starting with the actions that cause least damage to the soil or to other species.

  1. Start by trying to prevent pest outbreaks by growing strong plants, caring for the soil, practicing crop rotation, providing habitat for diverse natural predators,
  2. Next, by using physical controls (also called cultural controls) such as removing weeds that are host plants, using rowcover or netting, handpicking the pests if numbers are small enough.
  3. Monitor pest levels and assess if further action is needed. You can do this while hand picking. Many crops can take 30% defoliation without any yield reduction. In general, monitoring should begin at the seedling stage and continue until after harvest.
  4. When pest levels exceed the Action Level, and prevention and physical control have proved insufficient, biological, microbial, botanical and mineral control measures can be used to reduce pest damage of crops to an economically viable level, while minimizing environmental risks. There are four types of sustainable bio-intensive control measures to choose from, starting with the least toxic solution:
    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.
    2. Microbial controls refer to the use of fungi, bacteria, and viruses to kill pests. Bacillus thuringiensis (Bt) and the Entrust formulation of spinosad are acceptable if you have USDA Organic certification.
    3. Botanical control uses plant-based products for pest control. An example is neem oil.
    4. Inorganic (mineral) controls, also known as biorational disease controls, make use of oils and soaps.