1 of 7
2 of 7
Early blight on tomato leaves is noticeable as brown spots surrounded by a yellow halo. Remove symptomatic leaves to slow spread of disease.
Photo by Cory Tanner
3 of 7
Colorful squash vine borer moths may be seen flitting around squash plants late May through June. Their larvae (pictured) bore into and feed inside of squash stems.
Photo by Cory Tanner
4 of 7
Downy mildew symptoms are first noticed as yellow, angular spots on the leaves in mid-to-late summer. Spots eventually merge, killing the entire leaf. Trellis your cucumber vines to allow for quicker leaf drying to reduce infection.
Photo by Ginny DuBose of Clemson University
5 of 7
Small-seeded plants like tomatoes can be started in pots, then transplanted to the garden.
Photo by Cory Tanner
6 of 7
Young lettuce plants will do well when transplanted into the garden.
Photo by Cory Tanner
7 of 7
Corn earworm damage is typically restricted to the top third of the corn ears. Impacted ears are usually fine to eat. Simply cut off the damaged portion and wash the ear well.
Photo by R.L. Croissant, Bugwood.org
Dreaming of a bountiful summer harvest of tomatoes, squash, cucumbers, okra and corn? Dreading the mishaps that could bring your spring planting labors to naught? It pays to be vigilant, as voracious garden pests and sneaky diseases can turn a promising vegetable plot into a ravaged wasteland—sometimes overnight.
Good news: With a few professional tips and simple techniques, you can guard your favorite veggies against the most common garden threats, then reap the rewards.
Tomatoes
Hopeful gardeners set out tomato transplants between March and May, but these garden favorites can encounter multiple threats on the way to producing their anticipated summer bounty.
One of the worst early-season threats is cutworms, robust, soil-dwelling caterpillars that feast on tender plant stems while gardeners sleep. They hide in the soil during the day and emerge to feed at night. A morning walk through the garden reveals cutworm devastation in the form of young seedlings or transplants severed from their roots, wilting in the morning sun.
Fortunately, cutworms are vertically challenged. A simple stem collar can “foil” their feast. Loosely wrap a two-inch-wide piece of aluminum foil around your transplant’s stem at planting, and bury the collar one-half inch below the soil line. Or use a two-inch section of plastic irrigation tubing with a slit cut through one side so that it can be slipped around the transplant’s stem. These can be reused year after year, but clean them annually to avoid disease. Either barrier will prevent cutworms from severing the tender stems of your new crop. Once stems become tough and woody (pencil diameter or larger), cutworms no longer find them palatable and the collar can be removed, but removal is optional as long as the stem can grow without girdling.
Early blight disease is another problem that plagues tomato gardeners. This fungal disease attacks tomato leaves. It survives the winter in the soil and typically infects plants when soil (including spores) splashes onto leaves in the spring. The first symptoms show up as small, dark spots on lower leaves. As spring turns into summer, higher temperatures and humidity speed spread of the disease, and those small spots grow, leaving a bull’s-eye pattern within and a yellow halo surrounding the dead spot. The disease spreads rapidly up the plant, killing leaves as it goes. Left unchecked, it can consume most of the plant in just a few weeks.
The best prevention is planting tomato hybrids resistant to this disease. Look for disease-resistance listings in seed catalogs and Clemson Extension fact sheets. And give your plants plenty of space. Planting them six feet apart, with non-tomato relatives in between, can prevent the disease from jumping from plant to plant. A thick layer of mulch, straw or leaves helps keep soil from splashing onto leaves.
You can also slow the disease’s spread by removing lower leaves that develop spots. Deposit infected leaves in the trash, not compost. Finally, if both the disease and favorable weather conditions (hot and wet) are present, a fungicide may help. Products labeled for the vegetable garden containing chlorothalonil, maneb, mancozeb or copper fungicide may slow the disease if applied before it spreads too far
Tomato Quick Tips
• Wrap a collar around tender young stems to foil cutworms.
• Plant disease-resistant hybrids.
• Use mulch to protect lower eaves from soil-borne fungus.
_____
Squash and Cucumbers
Summer squashes (yellow squash and zucchini) are garden favorites that produce abundantly— if you can keep the squash vine borer away.
In early summer, these clear-winged moths lay eggs on squash plant stems. When the eggs hatch, larvae bore into the stem and feed on the vine from the inside. Protected there from predators and insecticides, they feed voraciously, growing larger and devastating the stem. Eventually your squash plants begin wilting from the damage. Inspection will reveal gummy, sawdust-like waste emerging from holes in the stems.
Delay the problem by planting your summer squash early. Vine borers don’t typically emerge until late May, so planting by mid-April lets plants become established and productive before vine borers attack. For later plantings, consider using row covers. These spun-bonded fabrics allow light, air and water to pass, but not flying insects, so moths can’t lay their eggs on stems. Cover your squash at planting, and leave the covers on until plants begin to flower. But row covers must come off at flowering to allow bees to pollinate the squash flowers.
Since insecticides can’t reach the destructive larvae already inside squash stems, they are not very effective against vine borers. But conventional garden products containing carbaryl or bifenthrin and organic materials such as Bt (Bacillus thuringiensi) and neem extract can provide some protection if they are applied to stems and surrounding soil before eggs are laid. Watch for brightly colored moths flying about during the day, then apply the product, according to label instructions, during the evening to avoid harming bees.
For plants that have been attacked but aren’t yet severely wilted, you can perform stem surgery. With a razor blade, slit the stem carefully lengthwise on one side. Then use a long needle to pluck the larvae out of the stem; destroy them. Cover the slit stem with soil and keep it watered. The plant should develop new roots and recover.
Another threat is downy mildew. This fungus can infect many gourd crops but is particularly damaging to cucumbers. Unlike powdery mildew, a less devastating disease that shows up as grayish-white powdery patches on the upper surface of leaves, downy mildew infects plants from the underside of leaves. The first symptoms are seen from above as yellow, angular spots that eventually spread, turn brown and consume entire leaves.
Downy mildew does not survive our winter. Its spores blow up from southern Florida each summer during windy, cloudy periods, leading to outbreaks in our state during warm, wet weather.
Dr. Tony Keinath, vegetable pathologist for Clemson University, has been the frontline commander for managing this disease in South Carolina. He recommends planting cucumbers early and trellising them.
“Cucumbers with downy mildew will stop producing fruit or fruit will be short and misshapen,” he says. “Keeping vining cucumbers off of the ground allows dew on the leaves to dry quickly, reducing the opportunity for infection.”
He recommends the General Lee and Marketmore 76 varieties. Both can get downy mildew, but the disease shows up later, allowing plants to produce fruit for a longer period. Fungicides containing chlorothalonil and mancozeb can be sprayed before vines become infected, but unfortunately, Keinath says, there are no organic sprays.
Squash & Cuke Quick Tips
• Plant squash and cucumbers early in the season.
• Protect young squash plantings with row covers.
• Keep vining cucumbers off the ground.
_____
Sweet Corn
If you’ve ever shucked homegrown sweet corn, you have probably encountered the mushy, brown remnants of a corn earworm. Maybe you’ve found the plump caterpillar responsible as well! Corn earworm is a common pest of sweet corn in the home garden—so common that 90 percent of the ears in an untreated planting will likely be affected. Fortunately, the damage is usually restricted to the top third of the ear.
Childhood summers on my grandfather’s tobacco farm involved large plantings of sweet corn. Many ears would be infested, but we would just cut off the damaged areas before cooking. If you find the damage unappetizing, a few tricks will discourage this pest.
First, plant early. Corn earworm is a late-season pest. Planting at the earliest date possible for your area can help avoid damage. Second, a few sweet corn varieties are more resistant to earworm. Country Gentleman, Stay Gold and Silvergent have tighter husks that slow earworms down.
Another low-impact trick is to apply five drops of mineral oil from an eyedropper to corn silks on each ear about five to six days after the silks emerge. Adding an organic insecticide containing Bt at the rate of one part Bt to 20 parts mineral oil improves effectiveness. Mineral oil blocks the earworms from getting through the silks. Don’t apply the oil earlier, however, as it can interfere with pollination.
Corn Quick Tips
• Plant early to avoid damage from corn earworm.
• Choose varieties with tighter husks that slow earworm penetration.
• Apply mineral oil to newly emerged corn silks.
_____
Okra
Okra has relatively few problems in the home garden, but planting too early is a common mistake. Okra is a hot-weather crop that hates cold soil. Wait until the soil temperature four inches deep is at least 65 degrees F. Okra seeded into colder soil will become stunted and never develop properly. A soil thermometer will check temperatures, but I’ve found that a simple meat thermometer is accurate enough.
When I was a kid, we soaked okra seed overnight in milk before planting, the theory being that it improved germination. In college I learned that soaking in water or freezing the seed provides the same benefit without wasting milk. Now I store okra seed in the freezer year-round, where it’s ready as soon as the soil warms sufficiently. I seed my okra directly in the garden soil, but it also transplants well.
Want to get a little jump on the season? Sow seeds in a sunny, warm indoor location a few weeks before your desired planting date.
Aphids can be troublesome to okra. They can also target tomatoes, squash and sweet corn but are often noticed on okra. Tiny insects, sometimes called plant lice, they use their syringe-like mouthparts to suck sap from plants. If their populations are heavy, they can cause flower and fruit drop and release sticky material, called honeydew, that attracts ants and covers fruits and leaves, which eventually turn black from sooty mold growing on the honeydew.
I call aphids “the jelly beans of the insect world.” They are plump, juicy, fragile insects that many other insects love to eat. My advice: Don’t reach for the spray bottle at the first sign of aphids. In short order, the pesky little guys will become lunch for a variety of beneficial insects. The aphids will all but disappear, and the beneficial insects will remain in your garden, seeking other pests to eat.
If the aphid population grows and significant crop damage is occurring, corrective action may be needed. My next line of defense is insecticidal soap. These products are sometimes labeled organic, are nontoxic to humans and mammals, and are relatively safe to beneficial insects. To work effectively, they must contact their target directly, so make sure you thoroughly coat aphid colonies, checking under leaves and other places aphids hide out. Products with neem extract and spinosad are effective, low-impact insecticides.
S. Cory Tanner is an area horticulture agent and Master Gardener coordinator for Clemson Extension based in Greenville County. Contact him here.
Okra Quick Tips
• Don’t plant okra in cold soil.
• Let beneficial natural predators (like the lady beetle larva above) take care of small aphid infestations.
• Coat larger aphid populations with insecticidal soap.
_____
Which is better: seeds or transplants?
Gardeners often ask me whether it is best to plant vegetable seed or to purchase transplants. My answer is “yes.”
Some plants perform best when seeded directly in the garden (beans, peas, corn); others do better when transplanted (tomatoes, peppers, okra). Some are fine either way (cucumbers, squash, melons). A general rule of thumb is seed size: large-seeded vegetables grow best when direct seeded; smaller-seeded crops grow best from transplants.
When shopping for both seeds and transplants, quality is key. Seeds purchased in sealed packets from reputable suppliers are generally high quality. Look for a “packed for” date on the packet. It should be within the current year. Older seeds can lose viability, especially if they’ve been sitting out on a store shelf instead of in a cold, dark refrigerator.
Transplants should be healthy, pest- and disease-free, and not root-bound. The most common mistake new gardeners make with transplants is buying them too large. One summer, I saw people lining up at a discount store to buy $50 tomato plants that were 3 feet tall and already loaded with fruit. Imagine how many tomatoes you could grow for $50 if you were to start from seed or even small transplants.
While tomato plants are fairly forgiving, most vegetable transplants work best when they are small and still able to establish healthy roots. If planted when over-mature or root-bound in their containers, many transplants will fail to establish and grow in your garden.
For more information about growing vegetable transplants, see HGIC 1259 on Clemson’s Home & Garden Information Center.
_____
Fighting against fire ants
Red imported fire ants are a nuisance in the yard and garden. Their stings are painful, and fire ants will occasionally damage vegetable plants. They’ll feed on okra pods, corn seedlings, broccoli stalks and other crops. In the vegetable garden, they create a unique challenge, because many of the pesticides that control them in lawns and other landscaped areas are not safe in the vegetable garden.
Fortunately, products with the active ingredient spinosad are approved for use in organic vegetable production. Very effective against fire ants, they come in both broadcast-bait and mound-treatment formulations. Baits, which are relatively inexpensive, are designed for spreading over a large area when ants are actively foraging (warm, sunny days) and tend to provide the most benefit in spring and fall. Mound-treatment products, on the other hand, are designed for direct application onto fire ant mounds, typically as liquid mound drenches. Mound treatments approved for use in vegetable gardens include either of the active ingredients spinosad or carbaryl. No matter which strategy you choose, read and follow the label instructions carefully. When misapplied, they are worthless.
A note of caution: Read labels to ensure you never use fire ant products containing acephate in the vegetable garden. Acephate, found in some commonly used treatments, is readily absorbed by plant roots and will find its way into vegetable fruits and leaves, posing a danger to both humans and animals.
To avoid pesticides, you can disturb fire ant mounds repeatedly with a shovel or hoe. This usually encourages them to relocate, but you can’t predict where—frequently, they simply set up shop somewhere even more annoying.
Visit Clemson Extension’s Home & Garden Information Center for more tips on managing fire ants.