is available from Mother Earth News Fairs Online here.
The Food Independence Course Part Two consists of eight video presentations, most of which come with pdf handouts. My contribution is Growing Asian Greens, and pairs nicely with the Guide to Asian Vegetables by Wendy Kiang-Spray, author of The Chinese Kitchen Garden: Growing Techniques and Family Recipes from a Classic Cuisine. Other topics include Dandelion Wine, Homemade Teas, Food Conversations, Passive Solar Greenhouse Design, Productive Growing from Home, and Growing Your Own Spices.
Easy DIY Cabbage Butterfly Decoy!
The Good Seed Co blog posted this lovely idea for protecting brassicas from those white butterflies Pieris rapae. It’s based on the discovery that the butterfly is territorial. If it sees a slightly bigger competitor it flies away. I have not tested this system, but it sounds like an interesting and fun project that costs next to nothing.
We don’t have many cabbage butterflies because we have both a predator – the paper wasp, and a parasite – Cotesia glomerata, a parasitic wasp that lays its eggs in small (first instar) larvae of the Cabbage White Butterfly, or Imported Cabbage Worm (as we call it in the US). Cotesia larvae emerge from the caterpillars after 15-20 days and spin yellow or white cocoons on or near the host which dies when the wasps emerge. We often find clusters of these cocoons (about the size of cooked rice grains) on the underside of brassica leaves.
I learned from Bryan O’Hara in No-Till Intensive Vegetable Culture that our friends, the Cotesia glomerata wasps that parasitize brassica caterpillars, and overwinter as pupal cocoons on the undersides of brassica leaves, will hatch out in spring on the very day the overwintered brassicas start to flower. The 20-50 day lifecycle needs brassica flowers, so don’t be in a hurry to cut down all your bolting greens! The flowers provide nectar for the adult wasps. The leaves, as we know, provide food for the caterpillars, which provide the host for the wasps to lay eggs in. The wasp larvae feed on the caterpillar until it dies, then pupate.
There’s an incredible National Geographic video of this cycle, showing parasitic wasp larvae swimming around inside a caterpillar, bursting out through its skin. The weirdest bit is that it is the dying caterpillar that spins the protective cocoons around the pupating larvae. And us who plant the brassicas that feed the caterpillars! Who is the farmer and who is farmed?
Average frost dates – the last one in spring and the first one in the fall – are useful to know when planning your crops. Once you’ve calculated your planting out date for various crops, you can work back to set sowing dates for the crops you’ll transplant, and bed prep dates for every crop. You can also make a co-ordinated plan that paces the work and doesn’t have too much in any one week, or any while you plan to be on vacation. You can calculate your first sensible planting date for each crop, your last one and perhaps some in-between ones to keep up supplies throughout the season.
You can use your average first fall frost date to make sure you don’t plant frost-tender crops too late in the season when you have no hope of them maturing in time for a harvest. You can extrapolate beyond the frost date to figure out when to harvest the more hardy crops. See my Winter-Kill Temperatures chart for useful tips.
By looking at the number of frost-free days in your area you can see whether to grow long-season tender crops like watermelons, or whether it’s only worthwhile if you choose fast-maturing varieties.
The Harvest to Table website is a trove of clearly explained information.
Average frosts are only averages. Actual frosts can sometimes happen two weeks either side of those dates. Frosts are only one particular temperature, and may not matter to the crop you’re planning for. Soil temperatures for germination and for planting are another important part of planning.
K-State Extension has a brief article on the importance of measuring your soil temperature.
Harvest to Table also has a list, ranked by temperature, so you can see what you can plant this week.
Scottish Climate Friendly Farming Video
Farmer Patrick Barbour, from Highland Perthshire, has won the search for Scotland’s climate friendly farming champion. Patrick’s innovative three-minute video entry, filmed at Mains of Fincastle, near Pitlochry stunningly illustrates the benefits of tree planting, species rich grassland, rotational grazing for cattle and sheep and stitching nitrogen fixing crops into pastures. It is available to watch at: Next Generation Climate Change Competition
Commiseration and sympathy to ice-blasted farmers and gardeners
Visits to my website shot up over the weekend. People are checking out my Winter-Kill Temperatures of Cold-Hardy Vegetables as they are dealing with temperatures considerably colder than they ever expected for their region. I hope you can find some helpful information there while you triage your crops into “OK with these temperatures, can be left alone”/”might die, need help”/”will definitely die, no point in trying to save them”.
Q and A
Next a couple of questions that people left on the contact form, that I thought others might be interested in.
Q1. Is there an easy way to figure out what vegetables I can plant to maximize my space and yield. I am not sure if its my soil or sunlight availability in my backyard garden.
A. Most vegetables do need at least 6 hours a day of sunlight, so as we get closer to spring, assess various spots in your backyard. Maximizing use of the space includes careful choice of plant spacing, but also following one crop with another, or squeezing crops in between others. There’s no quick answer. Search my site for Succession Planting, Crop Spacing, Choosing Crops.
Q2. I am currently looking for Onion seeds or seedlings to purchase for approximately 1hector to plant. We based in the Free State Area.
A. South Africa? Sorry, I have no idea what is available where you are. 1 hectare is a huge area for onions, especially if you have never grown them before. Use transplants, not direct-seeded onions. Choose varieties adapted to your latitude, or else they may never grow big, or may not dry down and store well.
Flaming can be used for weed control, pest control, or crop termination.
Our introduction to flame-weeding was via the first article I ever read in Growing for Market magazine. It was about flaming for pre-emergence weed control in carrots. It sounded like such an effective method that we bought a Red Dragon flamer and never looked back! I remember saying and writing that it worked so well it felt like cheating!
We use a handheld flamer attached to a propane cylinder that is in a wheelbarrow pushed by a second person behind the first. This person also acts as a “fire warden.” Some growers mount the propane on a backpack frame. Walking along the aisle between beds and wafting the wand diagonally back and forth across the bed takes about ten minutes for a 100′ (30 m) bed. Flame-weeding alone can reduce hand-weeding to one hour/100′ (30 m). Hand-weeding can be reduced to 6 minutes/100′ (30 m) by flame-weeding after using stale beds which have been hoed three or four times.
Stale seedbed flaming for weed control
In the stale seedbed technique, the bed is prepared and watered ahead of planting time and one or more flushes of weeds are germinated and flamed or hoed off. Flaming avoids bringing any new weed seeds to the surface. To sow large crop seeds into a seedbed that has already had the weeds removed (by flaming or other stale seedbed technique), you can use a stick seeder or easy-plant jab planter. Making furrows for small seeds will inevitably activate a few weed seeds along the rows.
Flame weeding, pre-emergence
Carrots, beets and parsnips are ideal crops for pre-emergence flame-weeding. They do very poorly with competition, and grow more slowly than weeds, consuming lots of time hoeing, cultivating and hand weeding to get good yields. Flame weeding can change all that, with pre-emergence either as part of a stale seedbed technique, or post-sowing.
The latter method is to prepare the bed, sow the seeds, water, and then monitor carefully. The day before you expect the carrots to emerge, flame across the whole surface of the bed. Use a soil thermometer and the table here to figure out which day to flame.
Table of vegetable seed germination as a function of soil temperature
Days to Germinate
People who use pre-emergence flame-weeding for carrots can use a few “indicator beet” seeds sown at one end of the bed to show when to flame. As soon as you see the red loops of the beet seedlings breaking the surface, flame the carrots. (But look for carrots too, just in case!) Beets are always a bit quicker than carrots in germinating. Note that beets are about half a day ahead of carrots at 50°F–68°F (10°C–20°C), but more than a day at 77°F–95°F (25°C–35°C). The challenge with carrots is to keep the soil surface damp until they come through. As an indicator for beet seeds, you can use a few radish seeds.
Another way to get an alarm call is to put a piece of glass over part of a row. The theory is that the soil under the glass will be warmer and the crop there will come up sooner than the rest. I tried this once, but the soil under the glass dried out, and those carrots came up later than the rest! Nowadays we have a “no glass in the garden” rule, for safety, so I use beets, the thermometer and the chart.
Potatoes can get impossible to hill when you’d like to if you have wet weather, and this is where flaming can save the day. Potatoes may be flamed at 6″–12″ (15–30 cm) tall, to kill weeds without damaging the potato plants. After that, flaming is not recommended.
Sweet corn can be flame-weeded after planting, either pre-emergence or, with care, after the crop is two inches (5 cm) tall, using a directed flame.
Onion and garlic crops can be flame-weeded when relatively mature. Flame-weeding can achieve as good results as hand-weeding using one-third of the labor. Flame-weeding can damage young plants (four or fewer leaves), so bide your time. Direct the flame at the base of the plants, in the morning, when the plants are turgid. This technique is for unmulched crops. Naturally, if you have used straw or hay mulch, flame-weeding is not such a smart idea!
Peanut seedlings can be slow to emerge, so pre-emergence flame-weeding may be helpful. The seedlings look somewhat like peas or clover. Because they grow slowly for the first 40 days, they will not thrive if you lose them in weeds (guess how I know?!).
Flaming for ending potato growth
Potato plants come to a natural end when the leaves die, after which no further growth can be induced in them. Once the tops die, the potato skins start to toughen up. If you are growing storage potatoes and are impatient for the end to come, you can mow off the tops or flame them, to start the skin-thickening process, which takes around two weeks. The potatoes are ready when you can rub two together without any obvious damage to the skins.
Flaming for pest control
Pest habitat includes all those half-wild edges and odd corners. You can reduce the pest count in these havens by mowing, hand weeding, or flaming. Be sure not to remove all the habitat for beneficial insects while you do this.
Colorado potato beetles can be tackled by flaming while the potatoes are less than eight inches (20 cm) tall, as an effective pest control measure. It won’t kill the potato plants. Choose a warm sunny day when the pests are at the top of the plants. Flaming can kill 90 percent of the adults and 30 percent of the egg masses, according to ATTRA.
Mexican bean beetles can be killed by flaming after harvest for that planting is finished. Flaming will kill the plants too. We used to plant six or seven successions of beans, every two weeks, then flame the old plants when the pest count got too high, and move on to a newer planting. Nowadays we buy the Pediobius parasitic wasp to deal with the MBB, and we can sow beans less often and harvest them for longer.
Flaming trap crops
Flea beetles can be lured by a row of mustard greens. They like the pungent compounds in brassicas. Once you have lured the flea beetles you need to deal with them before you create a flea beetle breeding ground. Flaming the mustard plants is one possibility.
Cucumber beetles have a preference for some particular squash varieties, which may be grown as a trap crop: Cocozelle summer squash, Seneca and Dark Green zucchini are all “cucumber beetle preferred”! When beetles accumulate in the trap crop, flame it or till it in.
Stink bugs: Russ Mizell has published a paper on trap cropping for native stink bugs in the South. He recommends buckwheat, triticale, sunflower, millet, field pea and sorghum. A succession of trap crops including these and others such as pumpkins, cowpeas and other small grains (which are most attractive in the milk or soft dough stage) could help. Flame the trap crops when the stink bug numbers in the trap crop build up.
Excerpted and adapted from Sustainable Market Farming
Root Crops to Plant in Central Virginia in October
We have now passed our last chances to sow root crops outdoors. But the exciting season in the hoophouse has just begun. In early October, we sow radishes in our hoophouse. See Root Crops in September for more about our succession of hoophouse radish sowing dates. We like Easter Egg (a multi-colored mix of red, plum, pink, purple and white varieties, that matures over several weeks), Cherry Belle, the fast, uniform red globes, and White Icicle, like baby daikon about 3” (7 cm) long. These three varieties all stay crunchy and tender. We have a dread of fibrous radishes! Most years we make a sowing at the beginning of October and another at the end, and these will feed us from early November until early February. The late October sowing lasts for 8 weeks, so it’s good to make sure we plant enough. Radishes do a lot to brighten up meals in December and January!
In mid-October (10/10-10/25), we sow our first of three plantings of hoophouse turnips. We like the very fast-growing and tender Hakureihybrid. It has short hairless tops which also make good eating. We sow this variety on the south side of the bed, leaving the other 3 rows for the taller varieties. We also like Early White Eggand Oasis, which are not quite as uniform as Hakurei, but are OPs and the seed is much cheaper. They produce more greens, which we value too. In the north row we often grow Red Round, a beautiful red-skinned turnip with tall attractive leaves. We also like Scarlet Ohno Revival, which has the advantage of hairless leaves. This is an Open Source Seed Initiative variety. The OSSI pledge: “You have the freedom to use these OSSI-Pledged seeds in any way you choose. In return, you pledge not to restrict others’ use of these seeds or their derivatives by patents or other means, and to include this pledge with any transfer of these seeds or their derivatives.”.
We thin the turnips as needed. If we sowed thickly, the first thinnings become baby greens for salad. Once the turnips are the size of marbles, we like to thin the plants to 3” (7 cm) apart and cook them whole, roots and greens together. The next thinning is to 6” (15 cm) and from that point on, we harvest the greens and roots separately. We get a ratio of one bucket of roots to two buckets of greens, which fits our needs perfectly. We like to mix the roots, as the one quarter of red roots adds a pop to the appearance.
Root Crops to Harvest in Central Virginia in October
We can continue harvesting beets (and beet greens), carrots, horseradish, kohlrabi, radishes, turnips (and turnip greens), and winter radishes outdoors. Once we have had a decisive frost we can harvest parsnips – the frost really improves the flavor. Our 9/6 sowing of hoophouse radishes will start to mature.
We tackle our process of clearing root crops and storing them, starting with celeriac (if we grew it this year). We start with the least cold tolerant roots and work our way to the most cold tolerant. This list is root crops only. See my list of Winter-Kill Temperatures of Cold-Hardy Winter Vegetables 2020 for a more complete picture of “Harvesting in Time”
Clear and store (in this order):
Sweet potatoes 50°F (10°C)
“White” Peruvian potatoes 32°F (0°C) approximately
Celeriac 20°F (°C)
Turnips 20°F (°C)
Winter radish 20°F (°C)
Beets 15-20°F (°C)
Kohlrabi, 15°F (°C)
Carrots 12° F (°C)
Parsnips 0°F (°C)
Wash, and store roots in perforated plastic bags in refrigerator or root cellar. We use a special measuring bucket lid to help new workers determine if roots are big enough to store.
Harvest sweet potatoes before soil temperatures go much below 55°F (13°C), or night air goes below 50°F (10°C). See the Special Topic below.
Harvest white potatoes when the skins have thickened. (When the skin is undamaged after rubbing two together. About 2 weeks after the tops die). See Harvesting Potatoes and Root Crops in June. Two or three days before harvesting, we spend the day removing the hay mulch from our 1600 row feet (488 m) potato patch to the compost area. Our potato digging machine can’t deal with mulch or heavy weeds. To fit with using machinery, we clear complete rows. We have a Perfect Potato Harvest Checklist. For fall harvesting we do the tractor work in the morning and pick up the potatoes in the afternoon, avoiding leaving any out overnight if it will be frosty. (When harvesting the March-planted potatoes in July, we do the tractor work early in the morning and start picking up the potatoes as soon as possible. We aim not to be outdoors after lunch when it’s hot, but if we need to, we will, as we don’t want ready-baked potatoes sitting on the soil!) Tractor time is 4 hrs x 2 people. Picking time is 30 people-hours.
For beets, we allow 6 people-hours per bed (360 row feet (110 m), and expect 2-3 50-pound (23 k) bags per bed. Cut the stems about ¼” (6 mm) above the root, to reduce “bleeding” when you cook the beets. I was reminded recently that not everyone knows that the easiest way to cook beets is to scrub them, boil them in the skins, drain and immerse in cold water, then simply slide the skins off. Hardly any wasted food and no wasted time.
For carrots, we allow 4.5-6.5 people-hours per (large) garden cart for washing, trimming and sorting. Plan to keep the last 15 minutes for clean-up. Divide the rest of the time available by 3. Use 1/3 of the time for digging, 2/3 of the time for washing and sorting. Add time to take to storage. Record yields. We take the carrot tops back and spread them across the beds. (fall harvest only ). In the spring and summer we take carrot tops to the compost pile, as the smell can attract carrot rust root flies. In late fall it is too late to sow cover crops to protect the soil, and the flies have gone to overwinter wherever they do that, so we spread the tops over the beds to provide some protection for the soil.)
Special Root Crop Topic for October in Central Virginia:
Harvest sweet potatoes
Here’s our method:
First roll up the drip tape. Harvest on 3 mild days – generally in the week that your first frost usually occurs (10/7-14). We expect our whole harvest of 800 row feet (244 m) to take 80 people hours. Allow 1/3 of the time for snipping, 1/3 for digging, 1/3 for crating and schlepping. Digging takes a bit less time than either of the other jobs. Even a few hours exposed to temperatures below 50°F (10°C) will cause chilling injury. (Frost on the leaves does not of itself damage the roots). Don’t leave clipped plants uncovered overnight. Don’t leave sweet potatoes outdoors. Clip the vines, dig carefully, set the tubers in plant-clusters to dry on the soil. Select seed tubers (healthy med-size tubers from high-yielding plants, no rat-tails). We save a generous 100 Georgia Jet, 100 Beauregard, 20 each of Bill Shane’s White and Jubilee. (These last two are unofficial names for varieties we were given and are maintaining for genetic diversity.)
Other Root Crop Tasks in Central Virginia in October:
Curing sweet potatoes and white potatoes
Cure sweet potatoes in collapsible, stackable holey crates (or in wooden flats with spacers for ventilation) and cover with newspaper on top, in a basement with the heater on, for 10-14 days (85-90°F, 27-32°C, 80-90% humidity) or longer if it’s cooler and drier. Use fans. Splash water on floor. Curing is complete when the skin is undamaged after rubbing two together. Restack the boxes (in a rodent-proof storage cage, if you are using an outbuilding).
Cure freshly harvested white potatoes in a root cellar at 60-75°F (15.5-24°C) for 2 weeks, with good ventilation, then cool cellar to lower temperature. See Special Topic for July. For weeks 2-4, the temperature goal is 50°F (10°C), and fresh air is needed about once a week. Our method of providing an air change in our cellar or adjusting the temperature is to leave the door open when the temperature will be closer to our goal than the current reality. It works well enough.
In May I gave information on planting sweet potatoes. Hopefully that went well for you, and by now you have a large patch of healthy green vines. Let’s keep it that way! Here I will tell you about what the growing plants need, and the pests, disease and afflictions to avoid.
This paragraph was included in Planting Sweet Potatoes, and I’m repeating it here, as a good reality check on what you can expect.
Regardless of how early in the season you plant them out, they will not make flowers earlier, or start making tubers sooner. Both flower and tuber initiation are triggered by day length. Each variety has its own internal clock. Most varieties take 90–110 days from planting out to reach a good size, if the weather is warm enough.
The first month or so after transplanting is the root development stage. Roots can go 8’ (2.4 m) deep in 40 days. Don’t be alarmed at the lack of above-ground action. The second month or so is the vine growth stage. The roots begin to store starch and sugar close to the stem base. During the last month of growth for that variety (3rd or 4th month), the potatoes develop. Make sure you dig them up before the soil temperature gets down to 55˚F (13˚C) – the week of the average first fall frost is about right.
Growing sweet potatoes – Three Ws: water, warmth, weed-free
The critical time to maintain sufficient moisture is after transplanting for at least the first 20-40 days while roots are developing. By now, most growers will be beyond this most-important watering period. But if it’s less than 40 days since you planted them out, keep the soil moist. Use your fingers to test the soil for dampness.
Once they are established, sweet potato plants are fairly drought-tolerant. But if you want high yields, they’ll need water once a week, either from the sky, or provided by you. Note that if you are using plastic mulch, rain won’t go through it, so I hope you installed drip irrigation below the plastic. If not, lay it on top, right beside the plants. Aim to provide an inch (2.5 cm) of water per week.
Sweet potatoes need warmth! Heat determines success; the number of days from planting does not.
Provided the weather is warm enough, most varieties take 90–110 days from planting out to reach a good size.
You can gain warmth in a cold climate, by planting inside a hoophouse or low tunnel covered in clear plastic. Ventilate in hot weather.
Growing Degree Days (heat units) are a tool for measuring accumulated heat, but you don’t need to calculate GDDs to get a good crop!
Early varieties take 1200 GDDs to grow a good crop.
To calculate GDDs, take the day’s high temperature (max) and the day’s low temperature (min) and add them together. Divide by 2 and subtract the base temperature of 55F. (Apologies to the rest of the world – I only know this method using Fahrenheit, but I’m sure you can find out how to do the calculations in Celsius). There are phone apps that will do the calculation for you.
Example: For a daytime max of 90F, and a night-time min of 70F, you get 25 GDDs – just about perfect for sweet potatoes. 90+70=160. 160/2=80. 80-55=25. At 25 GDDs a day, you theoretically only need about 48 days to get a crop. There are some other limits to daily plant growth – the likely minimum for a decent crop is about 76 days.
In a plastic tunnel, you can get 20 GDDs a day or more, rather than the 5 you might get outdoors.
Cultivate to remove weeds until the vines cover the ground, after which very little weeding will be needed.
If you have plastic mulch, walk through pulling weeds, and drop them on the plastic to cook. If you are growing on bare soil, hoe while the weeds are small, and pull if the weeds and the vines get ahead of you.
Weeding is generally not onerous because the sweet potato vines cover the ground within 6 weeks of planting and smother any newly emerging weeds.
Deer eat sweet potato plants at all stages, including digging out the roots in the fall. Dogs, fences and guns are the three most effective methods of deer control. The plants can be covered with row cover or plastic net for the growing season. Motion-sensor sprayers work well if maintained.
Rabbits eat the foliage. Plant the slips on black plastic to hold back weeds, then put wire hoops over the rows and cover with row cover for 3–4 weeks while the plants are young. Even after the plants are large rabbits can cause substantial losses.
Groundhogs dig and eat the roots. They can be trapped with baits of fruit. What’s for dinner?
Pocket Gophers search out sweet potatoes to eat. Their mounds may be hidden under the foliage and the plants may survive as they only eat the larger roots, leaving no crop.
Voles move in from grassy areas to live under the mulch and feed as fast as the roots form. They eat the roots from the top down leaving the outer shell in the soil where they have feasted. Cats are the best control.
Rats love the roots. Cats or dogs are the best methods of control.
Field Mice build nests under black plastic and eat the roots emerging from the ground.
Human “pests” of sweet potatoes
You can eat sweet potato leaves yourself and it takes several meals to reduce yields of the tubers. Some researchers working in Vietnam, discovered that harvesting 25%, 50%, 75% or 100% of the vines every 15, 20, or 30 days (ignoring the information about the season of the year and the varieties) gave the sort of results you might expect. Harvesting tops every 20 days gave highest yields of greens. Harvesting 50% of the greens each time gave highest total yields of greens. Harvesting not more than 25% or 50% of the greens each time gave the highest eventual tuber yields, after 120 days. Researchers in Tanzania came up with the clear information that harvesting three times at one month intervals gave the highest greens production, but the tuber yield was affected tremendously. Harvesting tops twice in a growing period proved the best in leaf production as well as root yields. So, clip 25-50% of the tops of each plant up to twice in one summer, and you’ll still get a good yield of roots.
Although there are many insect pests that feed on sweet potato vines and leaves, most do very little damage, and hunting them down is not justified.
Pests that feed on foliage
Sweet potato flea beetles – Tiny black/bronze oval beetles (1.6 mm long), with reddish-yellow legs, and ridged wing covers; make small shot-holes in leaves or grooves in the upper surface of the leaves. Damaged areas turn brown and die. See below about larvae.
Sweet potato weevil adults and larvae do feed on the foliage, but mostly go for the roots (see below).
Caterpillars of three kinds:
Southern armyworms – Gray-black larvae up to 36 mm long with green or pink tints; pale longitudinal stripes and pairs of triangular spots along the back; pale yellow heads with bright red-brown marks. They feed on leaves and tips of vines, and congregate around the bases of plants during the middle of the day.
Sweet potato hornworms – First instar: white with a black horn; later instars (up to 90 mm long): green or brown with black diagonal lines down each side and a black horn, with a green or brown head with black stripes. They defoliate plants and often hide under leaves near the bases of plants.
Yellow-striped armyworms – Pale gray-black caterpillars up to 45 mm long, with orange-yellow stripes along the sides and pairs of triangular spots on the back of most segments; brown heads with black markings and a white inverted V. They feed similarly to southern armyworms.
Potato leafhoppers – Wedge-shaped insects up to 3 mm long; green bodies with yellow to dark green spots. They usually jump rather than fly. They suck sap from the underside of leaves causing yellowing of leaf tips and margins.
Fruit or vinegar flies – Small yellowish red-eyed flies about 3 mm long. They hover around overripe or decaying produce. They may be found with their small creamy maggots in cracks in sweet potatoes.
Tortoise beetle adults and larvae – Long-oval shaped gold beetles, up to 8 mm long, with various black or red markings on their flattened, shell-like bodies. The larvae have dull yellow, brown, or green bodies up to 12 mm long and black heads, legs, spots, and spines. Long spines on the abdomen hold excrement. Adults and larvae chew the leaves riddling them with holes.
Spider mites – Tiny reddish or pale spider-like arthropods that feed on the underside of leaves. Heavily infested plants develop a yellowish, bronzed or burned appearance.
Pests that feed underground on tubers and side roots
Sweet potato flea beetle larvae – Thin white, cylindrical larvae, up to 5 mm long, with 3 pairs of legs near their heads. They make shallow, winding tunnels on the surface of sweet potato roots and sweet potatoes. The tunnels darken, split, and leave scars.
Sweet potato weevil adults and larvae –Snouted beetles 6 mm long with dark-blue wing cases, orange-red legs and thorax, and fat, legless, 9 mm grubby white larvae with pale brown heads. The beetles make small holes over the surface of sweet potatoes mostly at the stem end. The larvae tunnel inside the tubers, leaving frass, which causes the sweet potatoes to taste bitter.
White grubs (spring rose beetles) – Dirty white grubs up to 25 mm long with brown heads and 3 pairs of legs near their heads. They leave large, shallow feeding scars on the sweet potatoes.
Wireworms – Thin, tough, wire-like larvae with 3 pairs of short legs near their heads and prolegs at the end of the body. They initially create large shallow cavities in sweet potatoes which they later excavate into deep ragged holes. Three species, with colors from yellowish-brown to cream or yellow-grey. Heads are darker, brownish.
White-fringed beetle larvae – Yellow-white legless, 12-segmented grubs, up to 13 mm in length, with small, pale heads. They chew into the roots.
Afflictions of sweet potatoes (these are not caused by disease organisms)
Round chunky roots, low yield, purple color: Planted too early, too cold.
Low yield: Flooded or crusted soil 6-7 weeks after planting? Planted too early?
Rough irregular shaped roots: Heavy clay soils or organic matter above 2%.
Rattails – thin, tough, tubers: Hot dry weather, insufficient water.
Brownish skin patches, worse in wet years: Scurf fungus, Monilochaetes infuscans. More likely if too much compost was used. Stored roots shrivel.
Metallic black surface lesions, maybe covering most of the root: black rot fungus, Certocystis fimbriata. Internal decay is not deep, but the fungus may impart a bitter flavor.
Sunken brown lesions that may completely encircle the root: ring rot, Pythium
Sunken lesions that dry and may fall out: Circular Spot, Sclerotium rolfsii. May taste bitter.
Hard, dry, black, sunken spots developing in harvest wounds: Fusarium. Spots may become larger than 2″ (5 cm) diameter, but damage is not deep.
Pitting: Soil rot or soil pox fungus in the presence of water stress. Roots will be small and malformed.
Streptomyces root rot bacterium causes a similar rot.
Fine or coarse irregular cracks, browning of the surface; dry, corky, dark-colored clumps of tissue scattered throughout the flesh, becoming worse if roots are stored warmer than 60°F (16°C): russet-crack/internal cork, feathery mottle virus (yellow feathery patterns of leaves). Do not use as seed stock.
When to harvest sweet potatoes
Unlike white potatoes, which have the annual plant sequence of vegetative growth, flowering and dying back, sweet potato plants would go on growing forever if the weather remained warm enough. Choose when to dig them up, ahead of cold weather. The longer you wait, the bigger the potatoes, but you are gambling with the weather. Usually sweet potatoes are harvested in the week that the first frost typically occurs in your region. I have written plenty already in previous years about harvesting, so I won’t go into it here. See one of the links to those posts, or my slideshow, if you want to know what comes next, or your climate is considerably colder than mine in central Virginia.
PART THREE: Potato pests and diseases (this one, June)
PART FOUR: Harvesting potatoes (July)
PART FIVE: Storing potatoes (August)
PART SIX: Planning to grow potatoes again (September)
I have a whole chapter about potatoes in Sustainable Market Farming, where most of this information can be found.
See Root Crops in June for info on digging up new potatoes, if you can’t wait for them to mature!
See The Potato Association of America, Commercial Potato Production in North America 2010 for lots of interesting info, including planting in hot weather. (But hurry up, you need to have enough growing days left in the season to get them to maturity.)
Organic Integrated Pest Management involves tackling pest problems one step at a time with ecologically-based practices, starting with actions to reduce the chances of the pest ever getting a grip on your crops. I recommend the ATTRA online publication Organic Integrated Pest Management. Each of the 22 pages is a poster, complete with good photos and concise clear info. Because nightshades have a lot of fungal, bacterial and viral diseases, it pays to take action to minimize the chance of diseases attacking your plants.
Integrated Pest Management in Organic Field Crops Webinar from eOrganic
Biological IPM disease and pest reduction strategies for potatoes
Cultivate strong crops and provide healthy soil, sufficient space, nutrients and water, suitable temperature, and soil pH.
Choose varieties that resist the pests and diseases you most expect. Improve the soil tilth, drainage and aeration. Chisel plow or broadfork to break hardpan, or grow deep-rooting cover crops ahead of your potatoes. Maximize air circulation around the plants. Choose a bright, breezy location (avoid frost pockets as they also collect dew), orient the rows parallel to prevailing winds and give the plants plenty of space.
Add compost and cover crops to build fertile soil to support strong plant growth and help increase the diversity of soil microorganisms, building naturally disease-suppressing soil. Use foliar sprays of seaweed extract, microbial inoculants or compost tea to boost general disease resistance. Consult ATTRA for compost tea Brew one part of compost to 5 parts water by volume for 14 days before spraying.
Practice crop rotation to reduce the chances of pests and diseases carrying over from one crop to the next. For potatoes, it’s best to rotate away from nightshade crops for at least three years. We don’t manage this ideal of one year in four. In our ten-year rotation, three of our ten years are nightshades (one paste tomatoes and peppers, two plantings of potatoes).
Practice good sanitation. Clear old crops promptly, so they don’t act as a breeding ground for pests or diseases. Avoid smoking, especially near nightshades, and have smokers wash their hands with soap or milk before working with potatoes. Tobacco can spread tobacco mosaic virus (TMV) to nightshade plants. Avoid working potato plants while the leaves are wet. Remove and destroy diseased plants, especially for late blight. Clean tools in between use in one field and another. When the harvest is finished, till the tops into the soil to speed decomposition, or remove and compost or burn them if growing on a small scale.
Remove nightshade weeds (e.g., horsenettle, jimsonweed and black nightshade), which can be alternate hosts for pests and diseases.
Prevent soil splash-back onto leaves, to reduce outbreaks of soil-borne diseases. Use drip irrigation rather than overhead sprinklers.
Cover or protect the plants physically from the pests
mulches to stop soil-dwelling pests (CPB) moving up into your crops
netting or rowcover to protect from airborne pests (leaf hoppers, blister beetles)
Provide habitat for natural enemies and other beneficial insects. Farmscaping with sunflowers, peas, vetch, buckwheat or small grains, to encourage ladybugs and lacewings, can make insect control unnecessary in a good year. Ground beetles and bats can consume surface and air attackers before you even need to look.
Monitor your crops regularly at least once a week and identify any pests you see.
Introduce natural enemies of the pest (bacteria, fungi, insect predators or parasites). Try biofungicides for use against some diseases. F-Stop, T-22G Biological Plant Protectant Granules or other forms of Trichoderma can control Rhizoctonia, Fusarium and Sclerotonia. Soil-Gard (Gliocladium virens) can work against Rhizoctonia. Bacillus subtilis works against Rhizoctonia, and Sclerotonia. Mycostop (Streptomyces griseoviridis) can be used against Phytophthora, Alternaria, 35% hydrogen peroxide diluted to a 0.5–1% foliar spray solution may help control early blight. 1% solution = 3.7 oz in 124.3 oz water to make one gallon (1 ml:33 ml). There are commercial products such as Oxidate that are based on hydrogen peroxide, which is corrosive and challenging to handle.
Hand pick (or trap) and kill the pests if the pest population is above the action threshold. Many fruit and root crop plants can take 30% defoliation before suffering any loss of yield. Where the crop is the foliage, this may be too much, but people don’t east potato foliage!
Use biological controls (often derived from natural enemies) if the damage is still economically significant after trying the earlier steps in the process, including Spinosad or Bt.
Potatoes can be attacked by more than 150 insect pests. But don’t despair! In each region there are only a few species that could cause unacceptable losses of yield or quality. These losses can result either directly from the insects or indirectly by transmission of diseases.
Colorado potato beetle is the most common pest that potato growers get to deal with. The pink blob-like larvae of this beetle can eat enormous amounts of potato leaves while growing into bigger pink blobs. Left alone they can kill a planting. Acceptable amounts of defoliation without causing loss of yield are surprisingly high: 50%–75% of the top leaves on a young 6″–8″ (15–20 cm) plant, 25% on a 12″–16″ (30–40 cm) plant, a mere 10% at the critical full bloom stage (when the tubers are sizing up), and up to 25% once full grown. As with many pests, having a few of them is not important — it’s all about the numbers. Action to control CPB is only needed if the number of adults or larvae is higher than 1.5 per plant or egg masses exceed one per ten plants.
Crop rotation is effective, because Colorado potato beetles overwinter as an adult in the soil and when they emerge they have to walk around searching for a potato plant. CPB can have 1-3 generations a year. Even where two or three generations are usual, a significant portion of the summer generation adults go directly into the soil and become dormant. Eggs are laid in clusters of 20 or more. They look like ladybug eggs but are a stronger orange color – don’t kill the wrong ones! The beetle can go from egg to adults in as few as 21 days. There are four larval instars, with 75% of the total foliage destruction caused by the final and fattest instar.
Mulching with hay or straw can prevent CPB finding your potato plants – we never find them on our summer planting. Our unmulched spring planting is a different matter. I scout that field once a week, counting adults and larvae on a hundred randomly selected plants. As soon as I see more than 50 adults or 150 large larvae or 400 small larvae per 100 plants, I unpack the sprayer. I do a spraying with Spinosad, a fermentation product of a soil bacterium. It kills insects by over-stimulating their nervous systems. Spinosad kills a wide range of helpful and harmful insects too, so spray in the early morning or late evening when bees are not flying. Shake the bottle well, and mix following the instructions. Clean and triple rinse the sprayer. Do not flush in the creek or pond. Repeat in 6 days, but only if needed. Usually one spraying is enough, although I continue weekly checks. In the South, there can be three generations of CPB each year, so stay vigilant.
Prior to using Spinosad, we used Bt. The version of Bt for CPB nowadays is Bacillus thuringiensis var. tenebrionis. The kurstaki strain (such as Crymax) generally available in small quantities previously is genetically modified, so we stopped using it, not wishing to be part of any support for GMOs. Neem and Beauvaria bassiana can also kill CPB larvae.
Flaming when the potatoes are less than 8” (20 cm) tall, is another effective control measure for CPB. Choose a warm sunny day when the pests are at the top of the plants. Flaming can kill 90% of the CPB adults and 30% of the egg masses, according to Colorado Potato Beetle: Organic Control Options – ATTRA
Insects with piercing-sucking mouthparts damage potatoes by physical injury to the leaves, sucking out phloem, injecting their toxic saliva and possibly transmitting diseases. While potatoes can grow new leaves, there is still damage to plant health. Direct injury by sap-feeding insects can kill the plant. Soil-dwelling insects have only minor effects on yield, generally, but can reduce tuber quality and storage life.
Aphid-transmitted viruses cause greater losses than all other insect-related damage together. There are at least 9 aphid-transmitted potato viruses. Aphids can be reduced by farmscaping, planting flowers which attract ladybugs, lacewings and other aphid-eating insects.
Potato leafhoppers are a bad problem in central and eastern North America. They overwinter on the Gulf Coast. In spring, flying adults are transported north on upper level airstreams. Yield loss can occur before visual symptoms are obvious. Leafhoppers can cause leaves to shrivel and die. The initial effects are reversible if leafhoppers are controlled before leaf tissue is destroyed (“hopperburn”). By reducing the green leaf area, hopperburn affects photosynthesis and growth. The most vulnerable stage is when the tubers are bulking up. Leafhoppers can also transmit diseases. Trichogramma wasps parasitize leafhopper eggs. Garlic with insecticidal soap, sprayed early in the morning, especially on the undersides of the leaves, can control hoppers.
Potato psyllid occurs in the western U.S. Damage to the roots and tubers is caused by feeding nymphs, which can cause psyllid yellows. The first symptoms of psyllid yellows include stunting, loss of green color, leaflet distortion, reddish discoloring of new leaves, and the appearance of aerial tubers. Early action can stop and even reverse the damage. Adults cause little to no damage underground.
Wireworms (click beetle larvae) can tunnel through the tubers. Wireworms can live for 1-3 years, so crop rotation is important. Avoid planting potatoes the first year after turning under pasture or lawn. If you expect to have wireworms, plant small whole seed potatoes rather than cut pieces. Cut slices of potato can be used to trap wireworms (dig up the trap pieces each day and kill the wireworms.
Cutworms can eat the leaves from the bottom of the plant up (the opposite approach from CPB larvae). Once the plants are fully grown, up to 75% loss of lower leaves is unimportant. At earlier stages, if any cutworm damage is seen, dig around the stem, find and kill the cutworms.
Blister beetles can cause trouble later in the season, skeletonizing leaves and spreading a wilt. They contain cantharadin, which can cause blisters on the skin of unwary workers. Blister beetles can be trapped in crops of chard or beets next to the potatoes. The beetles are easier to see and catch in the trap crops than in potato foliage. If there aren’t too many it may be worth putting up with them, as their larvae are carnivorous and eat grasshopper eggs.
The potato tuber moth damages both foliage and tubers during growth, but the biggest losses occur in storage. Larvae inside the potatoes can continue their development in storage, filling the tubers with frass and letting in decay organisms. When commercial infestations are high, the crop is not worth harvesting because of labor costs to cull out the infested tubers.
Nematodes can be deterred by choosing appropriate preceding cover crops, or by applying 1-2 tons/ac (2240-4480 kg/ha) of crushed mustard seed meal to the soil before planting. This will also reduce early weeds and act as a fertilizer.
Before a plant can become diseased, three conditions must exist: a susceptible host, a disease organism, and a suitable environment for the pathogen. The choice of the disease control method should be based on an accurate identification of the pathogen and the disease.
Late Blight (Phytophthora infestans) is by far the worst disease to afflict potatoes. This is the disease that contributed to the famine in Ireland (caused by the profiteering of the English land-owners, who sold the barley and left the tenant farmers to subsist almost entirely on potatoes). The disease is caused by a species of a fungus-like oomycete or water mold (previously considered a fungus, now reclassified as protozoa) that blows in on the wind. It is worse in warm wet weather with cool nights. Late blight starts as “water-soaked” spots on the leaves. These expand into gray-black “scorched” areas, sometimes with a dotted white mold growth, especially on the underside of the leaves. Cut stems reveal a dark circle of infected tissue. The disease spreads rapidly, turning plants black, as if badly frosted, and can kill an entire planting in ten days unless stopped by hot dry weather.
The best defense is to always remove volunteer nightshades from your fields and compost or bury all crop debris. The disease spreads via cull piles, nightshade plants and petunias — it needs live plant material to survive. If you find volunteer potato plants popping up in early spring, it is best to pull them up! Spores survive winter in warmer climates and then blow north and uphill. Preventive action may be taken with sprays every five days of (toxic) copper products, hydrogen peroxide, Bacillus pumilus or Bacillus subtilis products.
If Late Blight occurs late enough in the season, you can save your crop by mowing off the foliage, raking it off and disposing of it, and leaving the field untouched for two weeks before harvesting whatever potatoes have grown. This prevents the spores getting into the soil and infecting the tubers. Disposing of large amounts of blighted foliage is no easy task. When I had to deal with Late Blight, back in the 70’s, we made a fire and gradually added more tops as the previous ones burned. This was a very smoky fire, polluting, and no doubt contributing to global warming. Digging a big hole and burying it all is probably better.
Early Blight (Alternaria solani) is a common fungal disease, which mostly affects stressed or older plants. It starts as small brown spots on the lower leaves, which conglomerate into brown blotches that are restricted by the leaf veins, and so they can be angular in shape. The lesions have a bullseye appearance – concentric circles with a yellow halo around each one. During warm humid conditions, the fungus steadily defoliates the plants, reducing yields. The disease is seed-borne, soil-borne and airborne, surviving on plant debris and nightshade weeds. Early blight (Alternaria solani) can appear late in the season, not just early, despite the name. The manifestation of blight symptoms can be minimized by growing strong healthy plants, supplying sufficient water, and spraying with compost teas. The beneficial fungus Trichoderma harzianum can give good results.
Black Scurf or Stem Canker fungus (Rhizoctonia solani) is worst in cold wet soils. Early in the season it can cause sprout death. On older plants, red-brown stem lesions develop into cankers, and the infection can spread to the tubers, which then become cracked and misshapen, and may have dead tissue at the stem end. There may be firm black sclerotia (small dried reproductive bodies) on the tuber. In future, get disease-free seed potatoes and wait for the soil to warm a bit before planting.
White Mold (Sclerotinia sclerotiorum) on the vines. If you want to prevent this in future, you could dust the seed pieces with the commercially available fungal antagonists Trichoderma viride and Trichoderma virens.
“I have actually been thinking of building a tiny house and putting it inside a big hoophouse, creating a living area that would include a yard, trees, and gardens – allowing me to snowbird in place in northern New England – but I’m concerned about outgassing, since I’d be there almost 24-7 most days (I work out of my home). Have you done any research on outgassing of hoophouses?”
A Tiny House is generally a residential structure under 400 sq. ft
First off, No I haven’t done any research about hoophouse off-gassing, but I wouldn’t worry about out-gassing from the polyethylene of the hoophouse. Other products are much closer to your nose: All the materials used to construct, preserve and decorate the house and all the products within the house, such as furniture, fabrics, soaps, appliances etc.
There are some other things I’d wonder about:
1.Temperature. When the sun shines, the interior of the hoophouse warms up. When the sun doesn’t shine, it doesn’t. Would you heat the tiny house? You’d have to avoid heating systems that could damage the plants.
2.Snowfall. When it snows, you need to remove the snow from the roof of the hoophouse. Some snow can be carefully pulled down from the outside. Usually we also walk around inside the hoophouse bouncing a broom on the inside of the plastic to move the snow off. You can’t do that if you have a house in the way.
3.Humidity. In the winter we grow cold-tolerant hoophouse crops. We are aiming for 65 F (18C). We need fresh air for the plants and to deter fungal diseases. It doesn’t work to keep the hoophouse sealed up and “cozy”!
4.Strong winds. In hurricanes and gales, hoophouses sometimes collapse or get destroyed. You don’t want to be inside when that happens.
5.Height. Our hoophouse is less than 14 ft (4 m) at the apex.
In conclusion I’d say it’s better to have a small patio seating area within your hoophouse for suitable sunny days, rather than plan to live inside all the time.
Do you value crop rotation in your hoophouse?
A reader in the Pacific Northwest wrote: “This winter I have been re-thinking my crop rotation plan after having some issues (with flea beetle larvae in the soil outsmarting my diligent insect netting of my brassica salad crops). These days I see intensive market gardeners seeming to not worry so much about rotation (i.e. Neversink farm, etc), and yet I’ve always been taught that it is such an important principle to follow. I reviewed your slideshows on crop rotation and also cool crop planning in the greenhouse (which briefly addresses salad brassica rotation with other crops). With how much space I have and the high demand I have for brassicas, for salad mix (mustards) and also the more mainstay cole crops, I had settled on a 2.5 yr between brassica crop rotation (but planting two successions of mustards in the same bed within one year, in the year the bed was in mustards, with a lettuce or other crop breaking up the successions, with the idea that they were very short day and also light feeder crops). Wondering if you think this just doesn’t sound cautious enough, or if this sounds like a reasonable compromise with not having more space to work with (and wanting to satisfy the market demand for brassicas).”
I replied: “Yes, I do think crop rotation is important. I do know some farms seem to have given it up. I think what you are seeing shows one reason why rotation is important. In our hoophouse, we do as you do, allocating brassicas to a space for that winter season and perhaps doing more than one round of brassica crops. Then moving away from brassicas for the next two winters. If doing that doesn’t get rid of the flea beetle problem, and you are being thorough about netting with small-enough mesh netting (sounds like you are, but maybe check the mesh size), then my next step would be spinosad when the flea beetles appear. You can spray the inside of the netting too, and close it quickly. It’s that or a longer rotation, which it sounds like is not financially viable. You could also try farmscaping and/or importing predatory insects (not sure if there are any), Are there beneficial nematodes that attack flea beetle larvae? These are things I don’t know about, but might be worth looking into.”
Researchers from the Max Planck Institute and the National Taiwan University found that when sweet potato plants are attacked by insects, they emit a bouquet of odors and start production of a protein called sporamin that makes them unappetizing. Neighboring sweet potatoes sense the odors and start their own production of sporamin.
Insect damage cause stress-response production of anti-oxidants
In a related piece of news, Agrilife Today from Texas A&M AgriLife Research has found some evidence that wounded plants produce anti-oxidants as a stress response, which may make them healthier for human consumption. Read the report here.
A reader wrote in that the European Fire Ant is now found in Toronto.
“There were two nests of these in my allotment garden 2018.
They actually moved the nest in order to be closer to the zucchini
plants. Hand on heart: I never had any cucumber beetles develop past
the instar stage. The ants did not eat the eggs but they ate the larvae
as soon as they hatched. Same for potato beetle. My neighbours had
the best cucumber harvest in history. What I’ve read is these Fire Ants kill colonies of native ants. Summer 2019 I had a Pavement Ant war that went on for days. Clearly the Fire Ants did not wipe them out. There are black ants and other smaller red ants
in my garden. The Fire Ants appear to have moved on for some reason known
only to themselves. Perhaps they too have enemies.”“There’s a guy with a Youtube channel who keeps ant colonies. AntsCanada although he is in the Philippines. What happened was the feral Pharaoh Ants invaded his colony of Fire ants and killed them. Pharaoh Ants are much smaller but perhaps that’s what gave them the advantage. We have Pharaoh ants in Toronto also. I spend a lot of my time looking at the little critters in my garden. Like red velvet mites: there were many in 2016. Have not seen a single one in two years now. “
October is the busiest month in our hoophouse! The bed prep, sowing and transplanting keeps us busy for 3 or 4 hours a day. Add in harvesting (peppers, radishes, salad crops) and hand-watering of new plants, and we’re there for a good half of each day. And then there are extra challenges. Yesterday, in tightening one of the strings that mark the bed edges, I managed to hammer a 6” sod staple right through the irrigation main line tubing, which was below soil level. I can hardly believe I did that! I even thought “Be careful not to stab the water pipe!” So I had to dig it up, find a coupler and fix it right away. Because at this time of year, we rely on the irrigation for all the new plants.
And the nights are getting colder. We intend to close the doors every night when the temperature will be below 50F (10C), and the windows if the temperatures will be below 45F (7C). We have been converting the doors at one end from hinged to sliding doors. They’re hanging on their tracks, but one door is jamming in the track, and we need more than a cursory look to fix the problem. So meanwhile, only 3 of the 4 doors close!
My book The Year Round Hoophouse, has a chapter on making end walls, including doors and windows. Writing that helped me decide to change our east doors. Here’s an excerpt from that chapter:
“For our 30′ (9.1 m) wide gothic hoophouse, we have a pair of hinged double 4′ x 8′ (1.2 x 2.4 m) doors at each end. Our doors open out and have to drag over the grass outside. We have found “rising butt” hinges to be helpful here. As the door opens, it rises on the curved base of the hinge, giving a little extra clearance above the ground. Each door fastens with a hook and eye to the wall when open (it will get windy!).I recommend considering sliding doors, with the track and hardware on the inside, if the tunnel is wide enough for the track needed to carry the size of doors wanted. This avoids problems in many weathers: rampant grass-growing season, snow season, strong winds. Some people purchase storm doors and use those, but they are not very big. Anyone with basic carpentry skills can make simple door and window frames, as they will be covered both sides in lightweight plastic and not need to be extremely strong.”
Sometimes in the cool weather we have problems with this secretive pest chewing holes in brassica leaves at night. The larvae 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, you can suspect vegetable weevil larvae. They especially like turnips, pak choy and the flavorful mustardy greens. We sprayed with Spinosad last Monday, then again on Friday, and this week (Monday and Tuesday) I’m not seeing any new holes.
Solarization is a method of killing pests, diseases and weed seeds near the surface of the soil by covering the soil with clear plastic for six weeks or more in hot weather. We use this method to help control nematodes in our hoophouse. 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!
I’ve written before about solarization to fight nematodes in our hoophouse.
“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!”
In June this year I wrote about using marigolds, sesame, Iron and Clay cowpeas as nematode resistant cover crops. We’ve also used winter wheat, and white lupins. See Our Organic Integrated Pest Management . Other cover crops that suppress nematodes include some other OP French marigold varieties (but avoid Tangerine Gem or hybrid marigolds); chrysanthemum; black-eyed Susan; gaillardia (blanket flower, Indian blanket); oats; sesame/millet mix. We decided against sorghum-sudangrass (too big), winter rye (harder than wheat to incorporate by hand), bahiagrass, Bermuda grass (both invasive), castor bean and Crotolaria (sunnhemp) (both poisonous, although newer varieties of Crotolaria have lower toxin levels, and I’ve been rethinking my opposition to using that), partridge pea, California poppy (both require at least one full year of growth) and some obscure vetches that weren’t available locally. We might have included Pacific Gold mustard (B. juncea), if we’d found it in time. Don’t confuse this with Ida Gold Mustard, which kills weeds, and is susceptible to nematodes.
Food Crop Choices
This list starts with the crops most resistant to Root Know Nematodes and ends with the most susceptible. I’ve included some “bookmarks” between categories, but it can also be read as a continuous list:
We came up with a collection of nematode-resistant winter greens, including radishes, Russian kales, Brassica juncea mustards (mostly salad greens like Ruby Streaks, Golden Frills, Scarlet Frills), and Brassica rapa var. japonica greens, mizuna and Yukina Savoy. We have since learned that Yukina Savoy is a Brassica rapa, not B. juncea as we thought, and that mizuna is Brassica rapa var. japonica with a less certain resistance, or perhaps Brassica rapa var. niposinica, or perhaps B.juncea after all (integrifolia type). We also grow scallions in the nematode-infested areas. Now I am looking for more nematode-resistant cold-weather greens.
After the winter greens this spring, we transplanted two beds of tomatoes, one each of peppers, squash and cucumbers, and put two beds into Iron and Clay cowpeas. The eastern ends where we had found evidence of nematodes, we transplanted French marigolds and sesame as stronger fighting forces.
When we pulled up the squash and cucumbers we found no sign of nematodes on the roots. One of the tomato beds produced no sign either, but the other one did. Our first response was to sow Iron and Clay cowpeas instead of the planned soybeans, but before the plants were even 2” (5 cm) high, we decided to solarize that whole bed. We now have small patches of nematode infestation in almost every bed, calling for a more nimble approach to crop planning.
Brassica juncea mustards to try
According to Wikipedia, Brassica juncea cultivars can be divided into four major subgroups: integrifolia, juncea, napiformis, and tsatsai. I did some searching for more B. juncea, especially large leafed ones. Some promising looking crops include these:
In April I did a pleasant phone interview with Harold Thornbro of the Modern Homesteading Podcast about how year round gardening in a hoophouse can increase yields and the quality of vegetables and extend the growing season.
The rest of this post is about the agricultural things I’ve changed my mind on in recent years.
The first one that comes to mind is where and how to sow leeks. In Sustainable Market Farming I describe sowing leeks in outdoor nursery seedbeds. We grow leeks for eating from October to March, so even though leeks grow very slowly and need 12 weeks to transplant size, we don’t need to sow them super early in the year. Also because they are so cold-hardy, they don’t need greenhouse conditions. To save greenhouse space, and the bother of watering so many flats, we took to sowing them outdoors. To make this work, you do need weed-free beds. Leeks compete poorly with weeds. Sometimes things went wrong. One year someone decided to “seed-bomb” the fresh bed with poppy seeds. Weeding those tiny leek seedlings was torture! Another time, an overenthusiastic worker ran our new exciting wheel hoe too far onto the bed and eradicated part of a row.
One year the leek seedling bed wasn’t ready in time to sow, and we sowed rows of seeds in a coldframe, after removing the winter spinach (or maybe we were still growing lettuce in the coldframes then.) This worked well. The next year we tried sowing the seeds in 4” (10cm) deep flats, and putting the flats into the coldframes right away (rather than germinating them in the greenhouse). Still no wasted greenhouse space! On very cold nights, we cover the coldframes, so it was a bit warmer than if we’d just sowed directly into an outdoor bed. The plants grew a bit quicker and we realized we didn’t need to start so early. They were easier to take to the field in the flats, compared to digging up the starts and carrying them in little buckets with water. We had reduced losses of seedlings, so we reduced the amount of seed sown in future years. It’s an easier system, with a more satisfying success rate.
Sunnhemp as a Cover Crop
Sunnhemp (Crotalaria juncea) is a warm weather leguminous cover crop that I’ve been admiring at various farms in the Southeast in recent years. I’ve been thinking it would be valuable ion our hoophouse and in our gardens. It fights root knot nematodes! I mentioned it recently at a crew meeting, only to be reminded that I previously spoke against growing it as the seed is poisonous! I’d completely forgotten my earlier opinion!
This summer cover crop can grow to 6’ (2m) in 60 days. It thrives in heat, tolerates drought, fixes nitrogen, suppresses nematodes, makes deep roots that pull nutrients from deep in the soil, and it dies with frost. It sounds fantastic, I really want to try it! It looks a bit like small sunflowers, and according to Southern Exposure Seed Exchange it won’t make mature seed above 28 degrees N latitude , so won’t become a self-sowing invasive in Virginia. Sow in rows 2’-3’ (0.6-1m) apart. If it gets too big, mow when plants reach 5’-8’ (1.5-2.5m) to prevent the stalks from becoming tough and hard to deal with. ¼ lb sows 250 sq ft. (¼ lb = 114 g, 250 sq ft = 23.2m2)
Sowing Sweet Corn
I mentioned earlier here, that I’ve changed my mind about the necessity to put up ropes over corn seed rows to keep the crows off. I suppose there are fewer crows these days, sigh. Not needing the ropes makes the benefits of sowing with the seeder greater than the benefits of sowing by hand, so long as we can irrigate sufficiently to get the seed germinated. When we sowed by hand we watered the furrows generously, which meant we did not need to water again until after the seedlings emerged. If we hit a serious drought, the old method could still be best. Overhead watering does germinate lots of weeds, including in the wide spaces between the corn rows, so we need to factor in the extra hoeing or tilling when we weigh up the pros and cons. So, I’m a “situational convert” on this question!
How to Kill Striped Cucumber Beetles
I wrote about these beasties here. We handpick the beetles in the hoophouse squash flowers, hoping to deal with the early generation and reduce future numbers. One year we had our first outdoor squash bed very close to the hoophouse and the beetles moved there. In desperation I used Spinosad, an organically approved pesticide. It is a rather general pesticide, and harms bees, so I carefully sprayed late in the day and covered the row with netting to keep bees off. It worked brilliantly, taking a fraction of the time that daily handpicking takes. I became a convert to that method, but no one else on the crew did, so we went back to hand-picking.
I used to maintain that life is too short to prune tomatoes, which grow at a rapid rate in our climate, and get fungal diseases, necessitating sowing succession crops. The past couple of years I have removed lower leaves touching the soil, and this year I reduced the sideshoots on our hoophouse tomatoes, which are grown as an early crop here.(We’re about to pull them up in early August, as the outdoor ones are now providing enough). I do think we got fewer fungal diseases, and the diseases started later compared to other years, so I am now convinced that removing the lower leaves is very worthwhile. We also got bigger fruit this year, which logically fits with reducing the foliage some amount.
Is There Such a Thing as Too Much Compost?
I used to think the more compost the better. Now I am more aware that compost adds to the phosphorus level in the soil. I wrote about that here. I am not as alarmist as some people about high P in our situation, but I do now think it is worth paying attention and not letting the levels build too fast. I have got more enthusiastic about growing cover crops at every opportunity, and finding legumes to include in cover crop mixtures at every time of year (see above about sunnhemp). I was already a cover crop enthusiast, but as my experience increased, I got my mind round more possibilities.
In my youth I was anti-plastic, If I were growing food just to feed myself, I’d probably still find ways to avoid almost all plastics, but growing on a commercial/professional scale (and getting older) has led me to appreciate plastics. I still don’t want to do plastic mulch, except the biodegradable kind, but I’ve come to accept durable light weight plastics for their benefits. Drip tape saves do much water, reduces weed growth. Plastic pots and flats are so much easier to lift! I do still pay attention and try to make plastics last a long time, and frequently salvage plastic containers others discard. I’m awed by the possibilities of silage tarps or old advertising banners, to keep down weeds without tilling and pre-germinate weed seeds so that when the covers are removed, few weeds grow. This was called by the awkward name of “occultation”, but is now more often referred to in English as tarping.
Lastly, I have a post on Mother Earth News Organic Gardening about hornworms, but you read it here first!
Here we are in July again, and here are the hornworms again! Yesterday, in two 80 ft (24.4 m) rows of tomatoes, I found 53 inches (1.35m) of hornworms! There were 24, varying in length from 1” (2.5 cm) to 4” (10 cm). Today I found even more: 42 caterpillars totaling 85” (2.2m)! They are stripping leaves and munching on the green fruit.
In our hornworm photos, you might notice ours are not the same as yours. Ours are tobacco hornworms, not tomato hornworms, but both are bad news and both attack tomato plants. Before Twin Oaks Community started here in 1967, the land was a tobacco farm. Tobacco hornworms have a red (not black) horn, and diagonal white lines, not arrowhead vees.
Hornworms hatch from eggs laid by the night-flying Carolina sphinx moth or Tobacco hawk moth. This year I did catch one of the moths, and kill it, but we still have plenty of caterpillars. The moths hatch from strange coppery pupae with pipes or spouts attached, which overwinter in the soil. Even our most vigilant caterpillar-hunting seems to miss some, which then drop to the ground to pupate. Another way to break the lifecycle is to close the hoophouse at dusk every night (and open it promptly every morning before it gets too hot), but we’ve decided not to go that route.
Hornworms often get parasitized outdoors by a tiny braconid wasp that lays eggs in the backs of the caterpillars. The larvae develop inside the caterpillar and then the pupae develop as white rice-grain-like cocoons sticking out of the back of the hornworm. Usually our friend the parasitic wasp doesn’t come inside the hoophouse and to get parasites into the hoophouse hornworms we have to bring in parasitized hornworms from outdoors. This doesn’t work so well, because the hoophouse tomatoes are a month earlier than the outdoor ones, and the hornworm cycle is well underway in the hoophouse by the time the parasitic wasps are in action outdoors. This year we’ve found several parasitized hornworms indoors in the past few days, and we are very happy.
Meanwhile, we are conducting hunting raids every morning. To find where the hornworms are working, first look at the upper leaves of the tomatoes. If they are stripped bare down to the ribs, that’s a good place to look. Hornworms only like the tender upper leaves. If there are intact newer younger leaves, it might mean there was a hornworm, but it’s been removed already, and the plant is recovering. Another sign of hornworms in the area is chewed fruit. Another sign is “pineapple poop” – miniature brown pineapples or hand grenades. If you see fresh poop, look directly upwards – remember the law of gravity. The size of the poop is, naturally enough, in proportion to the size of the hornworm.
Having determined there is a hornworm in the vicinity, the next task is to find it. You’d think it would be easy – a big striped caterpillar like that. Not so! They are the exact same shade of green as tomato leaves. Hornworms can look remarkably similar to curled tomato leaves. The white stripes mimic the veins on the undersides of the leaves.
When I find some signs, I gaze at the area, looking for discrepancies in the pattern – bare stems with lumps on them. Usually the caterpillar is on the underside of a chewed stem, and often (but not always) they have their heads raised. When you find one, get a firm grip, pull it off the plant (they have strong legs which hold on tight), drop it on the ground and stomp on it. The skins are quite thick.
If I still can’t see the worm, I stand still and sway a bit from side to side, viewing the plant from different perspectives. It helps if the top of the plant is back-lit, but I do always check both sides of the row, no matter where the sun is. Knowing the signs of hornworm grazing can save you time looking everywhere. Focus your attention on where you are most likely to find them, and you will get the most success in the least time.
Bt is an organically-approved pesticide spray that kills small caterpillars, without killing other insects. I don’t expect it to work on big hornworms. Hunting seems to be the way to go!