During the later stages of June and early July, it will become increasingly important to monitor corn and soybean fields for some important pests warned professor of entomology and crop sciences Extension coordinator Mike Gray.
"For many areas of Illinois, the dry and hot weather makes this recommendation even more important because crops are increasingly vulnerable to yield loss under these stressful conditions," he said.
Japanese beetles can now be found throughout the state of Illinois. They can cause injury and subsequent yield loss in both corn and soybeans.
In soybeans, Japanese beetles are one of many defoliators to monitor. Rescue treatments may be warranted if defoliation levels reach 30 percent prior to bloom and 20 percent between bloom and pod fill.
In corn, the key concern is the potential for excessive silk clipping. Plants that are under severe moisture stress are vulnerable to this type of injury because they cannot grow sufficient silk tissue to keep up with the beetles' clipping activity. During the reproductive phase of plant development, a rescue treatment may be needed if there are three or more beetles per ear and pollination is not finished.
Densities for this pest tend to be greatest along field margins in both corn and soybean fields. "Treatment decisions should be made only after scouting field interiors and border rows," Gray warns.
The adult western corn rootworm has emerged nearly one month early. In the fields where plants have not begun to tassel and shed pollen, beetles are feeding on corn-leaf epidermal tissue and will continue to do so until pollen and silks become available. "Leaf injury reduces the plants' photosynthetic efficiency, so some yield loss should be anticipated for those fields, particularly those that are under moisture stress," Gray said.
As silks become available, a rescue treatment should be considered if there are five or more beetles per plant, silks have been clipped to less than one-half inch of the ear tip, and the pollination process is not complete. While scouting for silk clipping, look for lodged or goose-necked plants. This is evidence of larval injury to root systems.
"If lodged plants are observed, dig up some of the plants, wash the soil from the root systems, and look for signs of feeding or pruning," Gray advised. "If excessive injury is found, contact your seed company representative."