There have been calls again this year concerning chinch bugs coming out of wheat fields and moving into adjacent milo fields.
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 the 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 take out several rows of milo next to the wheat.
Problems with this insect historically were 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.
Adults are small, black bugs about and eighth of an inch in length they have a distinctive black-on-white ‘X’ pattern on the wings. Immatures or nymphs are tiny bright red after hatching or larger red and black, wingless bugs, then darken as they approach maturity. All nymphs have a characteristic white band across the middle of the body, although this feature becomes partially hidden by the developing wing pads as it matures.
There are typically two generations per year of chinch bugs in Kansas. Second generation chinch bugs have been infesting emerging panicles and causing direct damage to grain over a much wider geographic area in the state in about the last five years. 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, only contact insecticides.
The risk of first generation damage is greater where sorghum is planted next to thin stands of wheat. Seedling sorghum is most vulnerable, and seven 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, if any to corn 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 size, 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. With the recent precipitation we have received, it will help the sorghum and feed to grow more rapidly and thus to withstand greater numbers of chinch bugs.
Using seed treatments: clothianidin (Poncho), imidacloprid (numerous products) and thiamethoxam (Cruiser) at planting can potentially decrease chinch bug damage and may protect plants for up to three 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.
Most often the damage is noticed only after several rows of sorghum or feed have been severely stunted or killed. Ideally treating promptly as migrations begin and before significant numbers of bugs enter the field and small plants are affected is best.
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. By now I suspect they have all moved out of wheat, since it is mature and the sorghum is more attractive for feeding.
Most currently approved insecticides have good efficacy against chinch bugs, if three factors are considered. First, it is important to use the full recommended rate of the selected insecticide, preferably applied in 20 to 40 gallons of water per acre. High gallonage ensures good plant coverage and enhances the movement of material into protected plant parts such as leaf sheaths, which increases the probability of contact with bugs. Second, the material should be applied with properly adjusted and calibrated equipment. Cone nozzles designed for high-pressure use will create smaller droplets and improve coverage. Third, the timing of the insecticide application is critical. Early morning applications are preferred because winds are calm (reducing drift), temperatures are cool (reducing volatilization of chemicals), and a large proportion of the chinch bug population will be on the plants and exposed to the application. None of the materials currently registered for use against chinch bugs has long residual efficacy and plants can outgrow the protection. Because peak migrations may continue for 10 days or more, monitoring is required to determine if additional applications to border rows are necessary.
There are several insecticides labeled for the control of chinch bugs listed in the K-State Research & Extension publication “Sorghum Insect Management 2018 which can be found on our web site at www.cottonwood.ksu.edu
If you have any questions or need further information, contact me at the Cottonwood District Extension Office, Hays at (785) 628-9430.
Stacy Campbell is a Kansas State Research and Extension agent in Hays for the Cottonwood Extension District Office.