Keeping up with the Cutworms

Marissa Schuh, IPM Extension Educator

As soil starts to warm and vegetables get in the ground, complaints about cutworms often follow. Minnesota is home to a few species of cutworms, some of which we can track and predict, and others we can’t. Regardless of the species, we have limited management options once we start to see damage.

A cutworm we can track: black cutworm

The most frequently destructive cutworm we see in Minnesota doesn’t spend the winters here.  Black cutworms only survive the winter in southern states, and fly up to Minnesota using weather fronts.  University of Minnesota uses pheromone traps to track when and where black cutworms are being deposited into Minnesota.  Depending on how many are caught, we can make predictions about how large the population might be and figure out when we should scout for damage. If you are farming in one of the counties in the below table, be on the lookout for cutworms, as there was a lot of black cutworm moths trapped in your area.

A summary on when and where black cutworms have been trapped. Based on this date, predictions of when we will start to see black cutworm damage is reported. Data by University of Minnesota field crops team.

All the cutworms we can’t track

Other species of cutworms we see during a Minnesota spring include winter cutworm, dingy cutworm, bronzed cutworm, and glassy cutworm.  These caterpillars all survive Minnesota winters in one way or another, and emerge at different times. Winter cutworms is the most cold tolerant of the bunch, emerging early in the spring and sometimes even being reported while there is still snow on the ground.

What they all have in common

Cutworm caterpillars aren’t able to do the characteristic “cutting” when they hatch, they start out by feeding on small areas of leaves. If we are seeing this feeding, we can potentially take management action before they’re old enough to snip plants.

Young cutworms making small holes in and on the edges of leaves. Photo: Bruce Potter, UMN.

For black cutworm, we can get an idea of when leaf feeding and cutting may start, for other species, we will just have to rely on scouting.  Again, these insects are often nocturnal, soo scout at dusk or first thing in the morning. If seeing damage but no caterpillars, lightly run your fingers in a circle radiating out from the plant. These caterpillars like to hunker down under a little bit of soil during the day.  Identifying these caterpillars is tough – they are pretty boring colors and lack patterns or obvious hairs. Please reach out if you think you’ve found the cutworm giving you grief, send pictures to mschuh@umn.edu or text 612.460.7462.

What can we do about them

A lot of cutworm management is a mixture of cultural practices and luck (does your area get a flush of black cutworms?).  

Cutworm moths lay their eggs on anything that is green. Depending on where you are in the state and how things are greening up, the green plants available for egg laying and caterpillar feeding can be limited.  Oftentimes, cutworms start their lives feeding on weeds or in grassy borders, and as the weeds get removed or mowed, caterpillars can move into crops. 

Cover cropping and tillage will impact this food-finding process. In field crops, research has found that no-till fields had more cutworm damage than fields under conventional tillage. Any field that has lots of green plant matter in the spring, be it an intentional cover crop or a flush of weeds, is more likely to be a spot where moths lay eggs.  Obviously insect management is just one of our goals, so if we are cover cropping or behind on managing weeds, and you have a history of cutworm damage, take time to scout, especially for the leaf feeding by young caterpillars.  

If we want to be more active in our cutworm management, we can play with residue management, but sometimes we may still need more tools.  If you have had cutworm losses in the past, a key thing to do is to scout for the leaf feeding damage of young cutworms.  This is the life stage most vulnerable to insecticide applications, and if we kill these caterpillars, they never get old enough to do their most destructive, cutting feeding.

As always, the Midwest Vegetable Production Guide is the best place to go for pesticide recommendations. Cutworms are in the databases under “caterpillars.”  Make sure to check labels for cutworms specifically.