The overwintered adults emerge in early spring and fly into small grains where they mate and produce the first generation. Most problems in milo or feed occur when large groups of immature, wingless nymphs migrate from maturing wheat fields and invade adjacent sorghum or sorghum/sudan hay fields where they attempt to complete development. They typically do not infest the entire field but can damage or take out several rows of milo next to the wheat.
Problems with this insect were historically confined to eastern and central Kansas, with damage beginning in May or June, but in recent years, chinch bugs have become more of a problem further west in the state.
Second generation chinch bugs have been infesting emerging panicles and causing direct damage to grain over a much wider geographic area in the state. Control of second-generation chinch bugs on large plants is difficult to achieve with contact insecticides because of their habit of hiding behind leaf sheaths, and no systemic materials are labelled for this use.
The risk of first generation damage is greater where sorghum is planted next to thin stands of wheat. Seedling sorghum is most vulnerable, and 7 to 10 bugs per plant will cause stunting, poor root development, stand reduction and even the death of some plants. Larger plants can tolerate more bugs, but severe infestations can cause stunting, lodging, and yield loss. Since corn is planted earlier and is larger and more resilient at the time of nymphal migration, damage can be minimal and usually confined to border rows. Late-season damage is typically spotty, but heading sorghum can be infested behind the panicle sheath which can cause incomplete exertion of the head.
Chinch bugs puncture vascular tissues to extract plant juices and secrete digestive enzymes that cause the breakdown of surrounding plant tissues. Feeding punctures also can allow pathogens to enter the plant. Consequently, damaged plants present a variety of symptoms including stunting, yellowing, wilting, and necrotic lesions.
The effect nymphal feeding has on plants depends to a large degree on the health and nutritional status of the plants. Growth stage and water balance are critical because small or drought-stressed plants have less ability to tolerate or recover from chinch bug feeding damage.
Using seed treatments: clothianidin (Poncho), imidacloprid (numberous products) and thiamethoxam (Cruiser) at planting can potentially decrease chinch bug damage and may protect plants for up to 3 weeks, unless the migration is heavy. Growers can use follow-up sprays on border rows if protection wears off before the end of chinch bug migration.
Before spraying the border rows of an affected field, a key consideration is to determine the growth stage that most of the chinch bugs are in. Because the nymphs are the ones feeding on the plants causing the damage, the adults do not feed and will soon fly away to lay their eggs. So if the majority of chinch bugs are in the adult stage, the damage has already been done. Adults are small, black bugs about 1/8 inch long with white wings folded over the back. Immatures or nymphs, are tiny bright red after hatching or larger red-and-black, wingless bugs, then darken as they approach maturity. A white band on the upper side of the first abdominal segment is visible until wing buds grow to cover it.
Most often the damage is noticed only after several rows of sorghum or feed have been severely stunted or killed. An insecticide spray can be used over the affected rows and approximately an additional 100 feet beyond. Also, spraying about 100 feet into the wheat stubble is advisable if chinch bugs are still coming out of the wheat field. High gallonage, 20 to 40 gallons of water per acre ensures good plant coverage and enhances the movement of material into protected plant parts such as leaf sheaths. There are several insecticides labeled for the control of chinch bugs listed in the K-State Research & Extension publication “Sorghum Insect Management 2017 which can be found on our web site at www.ellis.ksu.edu
If you have any questions or need further information contact me at the Cottonwood District Extension Office in Hays at 785-628-9430.
