By STACY CAMPBELL
Cottonwood Extension District
There has been an increase of insect infestations this growing season around the state.
Two of the more widespread pests have been lepidoptera larvae (worms): the fall armyworm and the armyworm. These pests have become problematic for our fall planted alfalfa, bromegrass, tritcale planted early for haying, etc. and have the potential to be problematic in our fall-planted wheat. It is advised to not get in any hurry to plant wheat.
Fall armyworm (FAW) – Larvae when mature are 1-1.5 inches long and have a variable color (green to black) with three prominent white lines down their back and a distinctive white, inverted ”Y” pattern on their face between the eyes. These larvae feed on just about anything green and are currently very active in our area and probably all of Kansas.
This moth does not overwinter in the Great Plains but migrates northward annually from southern states. It usually arrives in Kansas in July where it deposits eggs on corn, sorghum and other summer crops. Several generations occur and reproduction may continue through August and into September, putting early-planted wheat at greatest risk. Early-planted fields should be inspected frequently during the first few weeks following emergence.
The first sign of damage is “window-pane” injury caused by tiny larvae chewing on seedling leaves. The larvae, which are usually too small to be easily observed at this time, hide in or around the base of seedlings. Within a few days the larvae become large enough to destroy entire leaves.
Fields with 25 to 30 percent of plants with windowpane injury should be re-examined daily and treated immediately if stand establishment appears threatened. Larvae increase in size at an exponential rate, and so do their food requirements. Later instars, larger larvae do the most damage, sometimes destroying entire stands, and are the least susceptible to insecticides. Without treatment, problems can continue until larvae reach maturity or until a killing freeze.
In our area there are significant populations of FAW feeding in seedling and established alfalfa, bromegrass, early planted triticale for haying or grazing, etc. Scouting is important because they can destroy seedling crops quickly.
Armyworms (ARW) - Larvae are darker with several conspicuous light-colored stripes on both sides of their bodies, and they present a somewhat different problem than the FAW, because they do overwinter in Kansas.
Therefore, the larvae may be around when the 2025 planted wheat crop germinates. Thus, planting as late as possible is important, as is destroying all volunteer wheat well before wheat planting begins.
This is also important because it is the female moth that initiates the infestation by where she deposits her eggs, and she won't deposit any eggs unless she detects some greenery for a potential food source for the developing larvae. From past experience with armyworm infestations, they may continue to feed until temperatures dip into the mid-20s °F for a couple of hours, says Jeff Whitworth, K-State Extension Entomologist.
Army cutworms - One other worm to consider is the Army cutworm. These moths migrate back into Kansas in the fall, looking for any greenery on which to deposit their eggs. So, they will not be the same problem as armyworms, as their feeding will be ending this fall, but the army cutworms will just be starting their feeding and culminate in the common "Miller moths" in the spring.
The best ways to help mitigate an infestation in fall-planted wheat from any of these worms are to plant as late as possible and destroy all volunteer wheat well before any wheat is planted in your area.
Information provided by Jeff Whitworth, K-State Extension Entomology Specialist.
Stacy Campbell is a Crop Production Extension agent in the Cottonwood District (which includes Barton and Ellis counties) for K-State Research and Extension. You can contact him by e-mail at [email protected] or by calling 785-628-9430.