Agronomic Crop Insects – September 23, 2011

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Soybeans
In looking at fields at the end of last week and early this week, one of the main insects that can be found are green stinkbugs – mainly nymphs. This comes as no surprise and you may want to re-read a very well written article by my colleague at the University of Maryland, Cerruti Hooks, were he talks about stink bug populations in soybeans (http://dorchester.umd.edu/files/August_18_2011.pdf). As indicated in past newsletter, you will need to consider scouting fields for stink bugs until the latest planted fields reach the R-7 growth stage.

Small Grains
Be sure to sample fields at emergence for aphids, true armyworm and fall armyworm feeding. In past years, we have seen economic damage from all three insect pests. We have seen fields destroyed by armyworms in past years, especially in no-till situations. In many cases it has been true armyworm, although fall armyworm can also cause damage. Although there is no threshold available, you will need to watch for larvae feeding on small plants.

You should also consider the following factors when making a treatment decision for aphids in small grains. In general, cooler summer temperatures with adequate rainfall followed by a warm, dry fall are conditions that favor aphid development in small grains, especially in early planted fields. Early fall infestations of the green bug aphid (which causes direct damage to small grains as well as vectors BYDV) are favored by cool, late summer conditions. The following link provides good pictures of the major species of aphids found in small grains in Delaware: http://kentagextension.blogspot.com/2007/10/know-your-small-grain-aphids.html.

The main reason one would consider aphid control in the fall (except for greenbug aphid that causes direct damage) is the potential for Barley Yellow Dwarf Virus (BYDV) transmission. In areas where you have seen BYDV in the past, where you are planting early, or you have seen direct damage by green bug aphids, a seed treatment that control aphids (i.e. Cruiser and Gaucho) would be a good control option. Information from Kentucky indicates that planting date is the most important factor determining the intensity of an aphid infestation. If you have a history of aphids transmitting viruses in the fall and you plan to scout for aphids, data from the south indicates that the most important time for controlling aphids to prevent BYDV is the first 30 days following emergence. The second most important time is the second 30 days following emergence. The following link to a fact sheet from Kentucky provides more information on aphids and BYDV in wheat (http://www.ca.uky.edu/entomology/entfacts/ef121.asp).

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