All life stages of chinch bugs seem to be extremely active at the present time in both corn and grain sorghum. Nymphs and adults started migrating out of wheat fields at least two weeks ago, moving into any adjacent corn or grain sorghum fields. Those smaller reddish nymphs (Figure 1) have grown considerably since then, and are now either late instar nymphs or adults.
Figure 1. Stages of chinch bug nymphs. Photo by Holly Davis, K-State Research and Extension.
Many of these recently matured adults are now mating (Figure 2) and have even started egg deposition. These eggs are, and will continue to be, hatching which means more bugs and thus more feeding on these plants. Fortunately, most corn is large enough to withstand considerable feeding by chinch bugs. Plus, the recent rains greatly enhanced growing conditions, which increases the plant’s tolerance for chinch bug feeding.
Figure 2. Mating chinch bugs. Photo by Holly Davis, K-State Research and Extension.
Figure 3. Adult chinch bugs in the whorl of a corn plant taken the weekend of June 23, 2018. Photo by Holly Davis, K-State Research and Extension.
Most grain sorghum is much less developed than corn and won’t be able to tolerate as many chinch bugs as the larger corn plants. Treating plants much after the V6/V7 growth stages is not as effective as treating smaller plants. Like corn, good growing conditions significantly help sorghum plants withstand chinch bug feeding. However, if dry conditions return, chinch bug feeding can significantly weaken stalks and cause lodging later in the season.
For more information on chinch bugs, management decisions, and insecticide recommendations, please see:
Chinch Bugs, MF3107: https://www.bookstore.ksre.ksu.edu/pubs/mf3107.pdf
2018 Sorghum Insect Management Guide, MF742: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf
Jeff Whitworth, Extension Entomologist
Holly Davis, Entomology Research Extension Associate