Insect activity update for late July - Sorghum and soybean pests
Much of the sorghum around north central Kansas is at, or just coming into, the whorl stage. As the leaves unfurl and grow out of the whorls, a pretty high number of plants are showing large holes that have been chewed in leaves. These holes are from smaller larvae (most that we have sampled are corn earworms) that feed on the leaves while they are still furled. When leaves grow out of the whorl they have showy, ragged looking feeding that may cause concern.
Larvae sampled this week still have about one additional week of feeding within these whorls, then they will exit and crawl down the plant to pupate in the soil.
Larvae in the whorl are rarely worth spraying for four reasons:
1) By the time the leaves unfurl making feeding damage visible, most larvae have already accomplished most of their development and thus feeding.
2) Insecticides usually can’t penetrate far enough down into the whorl to actually impact the larvae.
3) A general insecticide will kill most beneficial insects.
4) Ragged-looking leaves during this stage have little to no effect on yield, and no, you cannot eliminate the next generation by spraying this generation.
Soybean Pest Update
Soybeans appear to be relatively pest free at the present time – but looks can be deceiving. There are a few small green cloverworms, thistle caterpillars, soybean podworms (corn earworms) and webworms, along with stink bugs and spider mites.
These pests are probably only going to increase in the next few weeks. Bean leaf beetle adults will also likely be emerging and showing up in fields soon. As the beans continue to develop so will the pests, thus monitoring should continue until beans senesce.
Jeff Whitworth, Extension Entomology
Holly Davis, Extension Entomology Research Associate