Update on insect activity in grain sorghum - July 27, 2018
Chinch bugs continue to feed and develop all around north central Kansas. However, growing conditions have improved significantly and thus the plants are much better able to tolerate this feeding.
As sorghum reaches the whorl stage, corn leaf aphids are becoming more common (Figure 1). These aphids may cause some concern as their honeydew production will occasionally be so thick and sticky as to retard the heads extending up from the whorl. This is not typically a field-wide problem, just a few places or plants in a field and these aphids are a good source of nutrition for beneficials.
Figure 1. Corn leaf aphids in grain sorghum. Photo by J.R. Ewing, K-State Research and Extension.
In addition, as sorghum leaves grow out of the whorl stage, they are showing signs of feeding. Fall armyworms have been feeding as small larvae within the whorl and as plants grow out and the leaves unfurl, these leaves have a very ragged appearance. Many of these ‘ragworms’ have finished feeding and are now pupating in the soil. Thus, spraying is not necessary as the damage is done. Even if the worms are still in the whorl, they will not be contacted by the spray. This whorl-stage leaf feeding doesn’t negatively impact the plant, or yield. There will probably be a least one more generation of fall armyworms and these may be more problematic if they start feeding in the head between flowering and soft dough stages. Feeding on these developing kernels is generally considered to cost 5% loss/worm/head.
For more information regarding sorghum insect pest management, please refer to the KSU 2018 Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf
Jeff Whitworth, Extension Entomology
J.R. Ewing, Entomology Graduate Student
Holly Davis, Entomology Research Associate