Midwest Pest Alert: What to Look For Early This Season

A recent article from the Michigan State University Extension Office identifies some key pests to watch for when scouting early this season. Both the MSU Extension Office and the Purdue Ag Center have seen an increase in armyworm and black cutworm in recent weeks.

The Purdue University trapping network has seen what they are referring to as “intensive” and “impressive” amounts of armyworm and black cutworm, while MSU has seen a drop in the numbers of these insects caught this week. Armyworms and black cutworms are an increasing threat with the current rainfall events, as they thrive in wet and weedy conditions.

Identifying black cutworm

The MSU Extension Office describes a few things to look for when trying to identify black cutworm larvae:

"They are light gray to almost black in color and have a greasy appearing texture and coarse granules of various sizes that can be seen on their skin."

Black cutworm larva. Photo by USGS Bee Inventory and Monitoring Lab.

Black cutworms lay their eggs on cover crops, crop residue and low, grassy or weedy areas, and the young larvae feed on weeds and seedlings. You can identify where they have been feeding by looking closely at weeds, where they will leave small pinholes. The older larvae feed below the ground, usually cutting off plants or boring through at the soil line. If you notice an area of plants that have wilted or died, this might indicate that there have been older larvae feeding in the area.

Identifying armyworms

When trying to identify armyworm larvae you can look for these features described the MSU Extenion Office:

“Stripey body, may be dark or light in color — Distinct dark bars on the prolegs — Reticulated head capsule (looks like paving stones)”

Armyworm larva. Photo by Steve Gower | http://www.msuent.com/assets/pdf/27AWCorn.pdf

Armyworms lay their eggs in areas with heavy vegetation, such as weed-ridden fields, wheat fields, or other cover crop fields. No-till corn fields are also at a higher risk of infestation.

Armyworm larvae feed at night and hide close to the base of the plant during the day. To identify where armyworm larvae have been feeding, look for a tattered appearance on corn leaves. Armyworm larvae can also be spotted by looking for cylindrical frass in the whorl of corn or on the ground. Wheat growers should look for larvae on leaves and clipped heads.

The MSU extension office also warns that,

“As small grains mature and dry down, larvae can ’march’ like an army en masse into neighboring corn fields.”

Signs of damage to your crop

If you notice heavy flights of these insects, that doesn’t always mean there is an infestation in one of your fields. Often times, the damage you see to your corn depends on how effective your weed control is, as these insects are most likely to lay eggs in areas that are weedy or grassy. The MSU Extension Office writes that,

“This year is a challenge given the recent rains and the density of the weeds in many fields. Herbicide applications made at or just after planting removes the alternate food source, forcing larvae onto the crop.”

If you’ve made a herbicide application at or right after planting, this is when you’re most likely to see the most damage to your crop. Recent rainy weather delaying planting this season might align your crop emergence with the larval life cycle, which could expose your crops to more larvae for a longer period of time.

How and when to scout

The MSU Extension Office recommends to start scouting for black cutworm “300 degree days after a significant flight in the area”, defining a "significant flight" as catching more than nine moths in a bucket trap over a two-night period. At this point, you can start walking your fields to look for cut plants or spaces in your rows.

Scouting for armyworm should be started around the next three weeks, according to MSU. When scouting, look for “leaf damage and frass or larvae in the whorl (larvae may be on the ground at base of plants)”. To better prioritize your scouting efforts, focus on non-Bt corn fields or fields where weed pressure is the heaviest.

The infestation of armyworm in wheat fields has a higher likelihood of being more severe and covering a larger area. When scouting, look for cut heads, leaf defoliation, and larvae at the base of the plants.

Black Cutworm. Retreived from: https://extension.entm.purdue.edu/fieldcropsipm/insects/black-cutworms.php

DiFonzo, C. (2017, May 4). Spring moth flights and infestation potential for corn and wheat. Retrieved from: http://msue.anr.msu.edu/news/spring_moth_flights_and_infestation_potential_for_corn_and_wheat

March of the Armyworms Part II - Corn. Retrieved from: http://www.msuent.com/assets/pdf/27AWCorn.pdf