By Gus Lorenz, Extension Entomologist
We have received several reports of armyworms showing up in Arkansas wheat. The question is, “Are they causing any damage?” The armyworm population is like the wheat, a little behind schedule due to the record cold spring we’ve had this year, and we continue to receive reports of armyworms in wheat that is flowering to early grain fill. The first question to answer is how many armyworms you have. The following information may be useful. Armyworms largely hide on the ground under litter during daylight hours and feed on the plant at night. They feed on the lowest leaves first and work their way up. So on these pretty sunshiny days we have right now, if you’re scouting for armyworm, you will have to dig under debris and look in soil cracks to find the armyworms. See how many per square foot you have. The first visible symptom is the lack of a lower wheat canopy where the leaves are completely consumed. Look under debris at the base of plants or in soil cracks to confirm the presence of larvae.
HERE IS THE MOST IMPORTANT THING TO REMEMBER:
The most important factor in yield reduction from armyworm damage is the developmental stage of the plant at the time of attack. Wheat in the late stages of development (soft dough and later) can be completely defoliated with no measurable loss to yield. Usually, armyworm populations build only late in the wheat production season when wheat has already reached this stage. However, this year because the wheat is late, you may still have wheat in the late bloom-milk stage when armyworms could reduce yield. If armyworms are feeding on the flag leaf prior to soft dough stage, severe defoliation in boot-stage and flowering wheat can reduce yields.
If defoliation is significant in fields still in the flowering stage, treatments may be warranted. Also, you should consider seed wheat a little differently. Refer to the University of Arkansas Insecticide Recommendations Guide (MP144) for the currently labeled insecticides. The best time to apply an insecticide would be late afternoon since the armyworm feeds primarily at night.
Arkansas thresholds do not recommend treating wheat once it has reached the soft dough stage even if plants are completely defoliated. However, in rare situations armyworm densities may get so large that they may cut the stem just below the head. Obviously, serious yield damage would result in these situations, so fields should be observed closely to determine if head cutting is occurring. The Arkansas threshold states that growers should “Apply insecticides when larvae are present and head cutting is occurring after wheat has reached milk/soft dough stage.” This threshold is based on sound research conducted here in Arkansas and much of it under extremely high numbers of armyworms. This threshold has the potential to reduce insecticide costs for growers and save money for growers.