Joanne Whalen, Extension IPM Specialist; firstname.lastname@example.org
In general, the decision to treat for corn earworms should have been made by now. If you have not scouted, be sure to check the latest planted fields. We are finally starting to see a decline in trap catches so hopefully we will not see another hatch. Overall, control has been good – especially if treatments were applied to threshold levels of small worms and the correct rate was used. If you sprayed last week for the first time, you will want to re-check fields this week to be sure you do not have another hatch of larvae.
Be sure to sample all fields at emergence for aphids, true armyworm and fall armyworm feeding. In past years, we have seen economic damage from all three insect pests.
When it comes to armyworm, we have seen fields destroyed 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. With higher trap catches for true armyworm throughout the summer, you will want to watch fields since damage can occur very quickly.
As you make plans for small grain planting, you should consider the following factors when making a treatment decision for aphids. 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 greenbug aphid (which cause direct damage to small grains as well as vector BYDV) are favored by cool, late summer conditions.
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 Viral (BYDV) transmission. As indicated in past newsletters, the plant pathologists in our area still do not feel that we are seeing a significant increase in the incidence of BYDV. However, in areas where you have seen BYDV in the past, where you are planting early, or you have seen direct damage by greenbug 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).