Overwintered adults emerge in early spring and fly to small grains where they mate and produce the first generation. Most problems in sorghum occur when large groups of immature, wingless nymphs migrate from wheat fields as the grain matures and invade adjacent sorghum fields where they mature and produce a second generation. Because the nymphs are flightless, various barrier treatments and trap crops historically have been used to protect the margins of emerging sorghum fields. Occasionally, adults fly into sorghum, either directly from overwintering grasses, late-maturing wheat, or from other sorghum fields.
Problems with this insect are generally confined to eastern and central Kansas, with damage beginning in May or June. The risk of 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 poor root development and stand reduction (Fig. 2). Larger plants can tolerate more bugs, but severe infestations can cause stunting, lodging and yield loss. Chinch bugs usually increase in dry periods and decline during wetter years. Outbreaks tend to occur in roughly 7- to 10-year cycles. Locally damaging infestations develop nearly every year, particularly in parts of south central Kansas. Growers should continue to monitor for chinch bug activity each spring, especially when moisture is limited during April, May and June and nearby wheat is thin and lacking in vigor. Damage by second generation chinch bugs can now be observed state-wide, but is of less economic importance and usually untreatable, given the size of the plants and the bugs' propensity for hiding in leaf axils and behind leaf sheaths. Damage is typically evident as reddish discoloration of the stalk below the panicle, or failed exertion of the head when the developing panicle is infested (Fig. 3).
Figure 3. Damaged sorghum head caused by chinch bugs.
