Agronomic Crop Insects – April 26, 2013

Joanne Whalen, Extension IPM Specialist;

Field Corn
As the first plants emerge, we often can see both cutworm and bird damage in the same field. In general, small cutworms feed on leaves before cutting plants. You can distinguish bird damage from cutworm damage by the pattern in the field. With bird damage, you generally see longer strips of damaged plants, plants pulled out of the ground, and/or plants cut high that are compressed at the base of the stems. Although birds can cut plants off at the soil surface, they tend to pull plants out of the ground. In addition, if you look closely you will see “bird prints” near the missing plants or holes where birds have pulled plants out of the ground. As a reminder, we do still have the 24(c) Special Local Needs Registration for Avipel Hopper Box (dry) Corn Seed Treatment for bird management on field corn in Delaware. The 24 (c) label should be on the pesticide canisters. If you need a copy of the label, please contact Dave Pyne at the Delaware Department of Agriculture.

Small Grains
In general, insect activity has been very low in barley and wheat. We have found a few barley fields with aphids moving in to the grain heads. With the current cooler weather, beneficial activity will lag behind increases in aphid populations. Once grain heads emerge, the treatment threshold for aphids is 20-25 per head. We continue to get questions about stink bugs and the damage potential in small grains. We can find low levels of native brown stink bug populations (not brown marmorated stink bugs) in barley and wheat. As indicated in last week’s newsletter, information from southern states indicates that wheat may be susceptible to native stink bug feeding at the milk and soft dough stages. They also state that it takes extremely high numbers to cause damage to heading wheat. Thresholds in the south for native stink bugs range from one per head to one per 5 to 10 heads. In addition, they find the highest populations of stink bugs along field edges, which has also been our experience.