Controlling Common Pests
This year a common question is how to control common insect pests of crops and vegetables, a task that is becoming more difficult. Farmers who use seed treatments and broad-spectrum insecticides to terminate pests generally also terminate the beneficial natural predators. Some common Ohio corn and soybeans pests include soybean cysts nematodes, stink bug, wireworm, seed corn maggot, black cutworm, and true armyworm.
Soybean Cyst Nematode (SCN) damage soybean roots and has six life stages, 3-4 weeks apart. Soybean damage looks like stunted yellow soybeans, generally in circular or oval areas where SCN egg populations are high. There are numerous predators to SCN including Endo parasitic fungi, predatory nematodes, mites, Collembola (jumping springtails), Enchytraeids (pot worms), rove beetles, and centipedes. Cover crops like cereal rye and annual ryegrass planted early in the fall when soil temperatures are above 500F may reduce SCN levels 60-80%.
The invasive brown marmorated stink bug has become a major pest to corn, soybeans, vegetable, and fruit crops laying 20-30 eggs on the underside of leaves with 1-2 generations and up to 5 generations in warmer climates possible. Stink bugs have many natural enemies including birds, bats, toads, and spiders. In the soil, assassin bugs, other predatory stink bugs, and parasitic flies can destroy their eggs.
Wireworms (click beetles) have a five-year life cycle with adults laying 100-200 eggs in the spring and early summer. Larva live in the soil until they mature into adults. Wireworms are a copper color, long, and slender. Wireworms damage corn and soybean seeds and cause seedling roots damage. Natural wireworm predators include centipedes, soldier beetles, wasp which infect their eggs, and parasitic nematodes. Metarhizium fungi are a great wireworm predator; infecting the eggs, larva, and pupae and may give up to 95% control. Metarhizium fungi infect up to 200 insect species in 50 families including root weevils, flies, gnats, thrips, locust, grasshoppers, grubs, borers, even mosquitoes.
Seed corn maggots have three cycles per years with the first cycle causing the most damage. Adult flies lay eggs in the soil where pupae overwinter. In spring, they burrow into seeds which reduces germination and they infect young growing corn and soybean seedlings. They generally cover an entire field with an estimated 1.2 million wire worms per acre possible. The maggot is a pale yellowish white color. Seed corn maggots are more prevalent in cold wet springs and may be a problem this year.
Natural seed corn maggot predators include black ground beetles, predator nematodes and several fungal disease organisms including Metarhizium fungi. Ground beetles (Carabidae) are called the “Lions of insect pests”; eating their weight daily in weed seed and insect eggs, larva, and pupae. Ground beetles are highly susceptible to most neo-nicotinoid insecticide seed treatments (Cruiser, Poncho, Gaucho). They only lay 10-20 eggs per year and have a five-year life cycle, so they are slow to recover after broad-spectrum insecticide use.
The black cutworm moth migrates in from the South and lays eggs in green fields starting in March-May. Eggs hatch in May and the larva feeds on corn roots and leaves. The black cutworm larva (black striped) can be hard to scout because they are nocturnal. They often burrow in the soil around infected plants or in the whorl of leaves. They can circle young seedings and cut off the emerging vegetation. For home gardeners; coffee grounds, egg shells, and corn meal can be natural deterrents.
Black cutworm predators include fireflies, paper wasp, soldier beetle, ground beetles, rove beetles, parasitic nematodes, spiders, and toads. Fireflies live in the soil for 18 months consuming many insect eggs, larva and pupae. When they emerge in June, they mate, lay their eggs, then die rather quickly. Fireflies are hurt by over use of insecticides and night lights. Night light illumination confuses the adults and prevents them from breeding as they search for a mate.
The true armyworm thrives in green cover crops. The armyworm moth migrates from southern states in April-May looking for green vegetation, especially grasses and dense weeds. The moths lay 2000 eggs with 2-3 generations or waves spaced 3-4 weeks apart. The larva generally migrates to grassy plants like corn and wheat in early May. True armyworm seems to be especially attracted to cereal rye and corn planted into rye. The best time for rescue sprays is when caterpillars are 0.5 inches or smaller. The most severe crop damage occurs when the caterpillar larva are 1.5 inches long but by then they are much harder to terminate. Ground beetles, rove beetles, and 12 species of parasitic wasp and flies help control true armyworm. Next week my article will focus on methods of increasing beneficial insects and predators.