Corn and wheat growers should be prepared to scout wheat and corn fields in the later part of May and into early June for possible damage by black cutworm and/or armyworm larvae. The reason for this is because high numbers of black cutworm and armyworm moth catches have been reported from surrounding states over the past couple of weeks. Both of these moth species migrate into our area, lay eggs, and the developing larvae can be significant pests of corn and wheat. Andy Michel, OUS Extension agronomic crop entomologist, provides the following summary regarding each of these pests:
- Black cutworm—Female moths like to lay eggs in fields with heavy weed cover; weeds like chickweed are especially favored by black cutworm. As these weeds are killed by tillage or herbicide, the larvae move to emerging corn. Although there are some hotspots for egg laying, these predictions are far from exact. Insecticidal seed treatments do not offer much protection, and tank-mixing an insecticide with early burn-down has limited efficacy if scouting has not been done to see if larvae are present. Instead, we recommend rescue treatments which are very effective in controlling damage. If more than 3% of corn plants are showing damage, and corn is in the V2-V6 stage, and larvae are less than 1 inch, treatment may be needed.
- Armyworm—Female moths like to eggs in grasses, especially wheat, where egg hatch occurs over a couple of weeks. As the larvae develop, they can defoliate wheat plants, leading to yield loss. If corn is planted into wheat fields or other grassy cover, then, like black cutworms, armyworms can also move onto corn. Again, like black cutworm, the best way to control armyworm is scouting and rescue treatments. We rarely see economic damage from armyworm, except in outbreak years and it is too early to know if this year is an outbreak.
Another control option is the use of transgenic corn. Some transgenic corn varieties will provide control for both pests. For a list of which varieties provide this type of protection, take a look at this handy Bt trait table developed by Dr. Chris DiFonzo at Michigan State: http://msuent.com/assets/pdf/28BtTraitTable2015.pdf.
The big concern over the next few weeks will be egg hatch and larval growth. Both hatch and growth is difficult to predict and is largely based on temperature and growing degree days. From the projected temperature outlook, we could see 3rd or 4th instars of black cutworm by the 2nd or 3rd week of May, depending upon our actual weather.