Doug Johnson, Extension Entomologist
|Figure. 1. Armyworm moth|
Though delayed by several weeks, capture of armyworm moths in the UK-IPM pheromone baited traps is starting to show a definite increase. The delay is not unexpected given the very cold winter and cool wet spring we have had so far; but the size of the population is still in question for the same reasons.
The most recent data point at Princeton (April 25) consisted of 126 moths for the week, down just a few from the previous 135 moths per week. This is not much of a difference and given the poor flight conditions (wind rain & cold) over the past week, this difference is likely not of significantly different from the previous week. Though both of these counts are above the rolling five year average, they are still below the numbers we have associated with known armyworm out breaks.
The most recient data point at Lexington (April 25) is a big larger. Unfortunately, the data from Lexington has always had a much larger variation, and has not proven useful in making predictions when populations are this small.
(See current graphs at http://www.uky.edu/Ag/IPMPrinceton/counts/taw/tawgraph.htm).Typically, most wheat fields will have some armyworm in them, but usually the population is too small and the plants are too advanced toward maturity to be in any economic danger. The question this year will be how delayed is the wheat compared to the armyworm population, and how large will the armyworm population become. Both wheat and armyworm grow rates are based primarily on temperature. However, we will not know for a few more weeks how the winter affected armyworm overwintering and spring development. If both armyworm and wheat growth rate are reduced by an equal percentage, we are unlikely to have a problem. If however, the wheat is delayed significantly more than the armyworm, and / or armyworm survived the winter better than on average, economic damage is possible. At present I would guess that economic losses is doubtful, but let’s see how the flight continues. Nevertheless, we expect significant warming in the next week, with less disruptive rain events. I would expect that this weather pattern would be supportive of a large increase in moths captured IF the population really has growth potential. We should have a better idea before the feeding stage appears in any dangerous numbers.