I have heard of several damaging chinch bug infestations in the last week. Two reports were from pearl millet, the other from a mixed stand of grasses that included barnyardgrass. Small grains, summer annual forage grasses, corn, and turf grasses are all hosts of chinch bugs (Blissus spp.). Chinch bugs puncture plants with their syringe-like mouth parts and suck out the plant juice. They tend to feed at the base of the plants. Feeding causes different symptoms on different crops. The image below shows damaged corn from west central Alabama in 2004. The base of the stalk was discolored, brittle, and starting to lodge. Damaged plantsof other grasses may be tinged with purple or yellow, or they may turn completely brown. Plants become distinctly stunted. The base of the stem may become brittle, causing the plant to snap off near ground level.
Chinch bugs overwinter as adults, and become active when warmer temperatures return in spring. Adults lay eggs in protected crevices of grass plants, most often near the base of the plant. After about two weeks, chinch bug nymphs hatch from the eggs and begin to feed. Young chinch bugs are yellow or reddish brown with a white band running across the back. Older nymphs are black, with visible wing buds. Adults are black with white wings. Populations of chinch bugs build as the summer progresses. This makes summer annual forage grasses particularly vulnerable to damage. There are 2-3 generations per year in Alabama. This image shows the various stages of the chinch bug, and shows that when you find one chinch bug, you unfortunately usually find a lot more (courtesy Art Cushman, USDA Systematics Entomology Laboratory, Bugwood.org).
Chinch bugs spend much of their time feeding in protected places on the plant, hiding in cracks in the soil, or hiding under crop debris. They tend to be worse in dry weather, perhaps because heavy rains can kill chinch bugs. The rain also closes up many of the cracks and crevices in the soil, leaving fewer places for the chinch bugs to hide.
Once chinch bugs are in an area, they can be hard to get rid of. Chinch bugs can move from one grass crop to another as the season progresses. Forage producers who grow winter forage grasses and summer annual forage grasses in close proximity can inadvertently create a haven for chinch bugs by providing a year round habitat. Chinch bugs also can be an unwelcome side effect for farmers who grow susceptible crops in a continuous conservation tillage system.
Because chinch bugs feed at the base of the plant, in protected locations, they are very difficult to control with insecticides. You can increase the chance for success by directing a spray application down to the base of the plants, and by using a high gallonage of water per acre (25-35 gpa). An insecticide application for chinch bugs is most likely to pay off in young corn or sorghum that has been planted in rows. It is difficult to get insecticides down to the base of a broadcast-seeded crop or a crop with narrow-row spacing. Insecticide and other pest management recommendations for most crops can be found in ANR-0500-A, Alabama Pest Management Handbook Vol. 1. Keep in mind that most insecticides have some form of a grazing interval. This means that livestock need to be removed before the insecticide application, and not allowed back in the field until after the specified grazing interval. Insecticide seed treatments, if they are available, provide a few weeks of protection from chinch bugs, but cannot provide season-long control.
One solution to chronic chinch bug problems in conservation tillage systems is to temporarily break out of conservation tillage. Accumulated crop residue can be turned under by deep plowing, giving chinch bugs fewer places to hide. When the new crop is planted, an insecticide seed treatment or an at-plant insecticide can be used to deter any remaining chinch bugs. If needed, 1-2 foliar applications of insecticide can be applied post-emergence. Growers following a mandated conservation tillage program may be able to petition to be allowed to perform this one-time, deep tillage in order to get rid of chinch bugs.
Chinch bugs feeding is less deleterious in a vigorously growing crop. Therefore, proper fertilization, timely seeding, good weed control, and irrigation can lessen chinch bug problems. Use of a crop rotation that includes non-host crops has also been suggested for chinch bug control. Legumes are not hosts, and may be a good choice for an alternative forage.
Kathy Flanders, Forage Entomologist, firstname.lastname@example.org
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