Greenbugs, armyworms, and fall armywoms infesting seedling wheat
During the week of Oct. 27-31 we received a report from Phillips County of greenbug infestation on seedling wheat (Figure 1). The unusually warm weather over the past few weeks, combined with prompt germination of this year's wheat plantings, have likely contributed to this occurrence. Winged aphids originating in subtropical latitudes are carried by air currents over Kansas virtually all year long, but fall infestations of seedling wheat by greenbugs are relatively rare this far north.
Given the recent favorable weather conditions for greenbug establishment, wheat farmers would be wise to check their fields for signs of greenbug damage. A single hard freeze should be enough to kill them off, but a few hours of subfreezing temperatures, such as those forecast for central Kansas Saturday night, might not be enough. Note that the threshold for greenbugs in seedling wheat is 50 aphids per row foot, or even fewer if the stand is sparse. If infestation is found, be sure to carefully determine the area affected and restrict treatment to this part of the field.
Figure 1. Greenbug infestation of seedling wheat. Photo by JP Michaud, K-State Research and Extension.
In addition, armyworms and fall armyworms have been very active in central Kansas over the past couple of weeks. Both worms will feed on leaf tissue above ground and consume more and more as the worms get larger.
Figure 2. Armyworms in seedling wheat. Photo by Jeff Whitworth, K-State Research and Extension.
The armyworm larvae in the photo below have been feeding on wheat, but started in forage sorghum. As the wheat germinated, these worms moved from the sorghum to the wheat. This was regrowth forage sorghum and thus was still very green and succulent. However, for some reason, after feeding a little in the sorghum, all the armyworms and fall armyworms then moved to wheat (see Figure 3).
Larval feeding has defoliated much wheat in patches in these fields. However, the wheat seems to have already established a root system. This armyworm feeding will reduce the capacity to utilize these fields for fall pasture but probably will not impact the stand too much. These larvae are mostly finished feeding and many are already pupating (see Figure 4).
Figure 4. Pupating armyworm. Photo by Jeff Whitworth, K-State Research and Extension.
This late in the fall there should not be another generation of larvae this year. Armyworms may overwinter as larvae or pupae, thus may survive the winter and emerge as adults in this field next spring. However, the wheat should be tall enough by the time this generation starts feeding in the spring that leaf defoliation will be negligible.
For more information and the most current Wheat Insect Management Guide for treatment options:
(Note: This article comes from Kansas Insect Newsletter, October 31, 2014:
JP Michaud, Entomologist, K-State Agricultural Research Center-Hays
Jeff Whitworth, Extension Entomologist
Holly Schwarting, Entomology Research Associate