Pest Alert №3 — Black Cutworms

Black cutworm or Agrostis ipsilon is the larvae of a moth and can be problematic on golf greens and tees. This week on a course visit we observed our first cutworm damage on a green. It is caused by a single cutworm feeding from a central hole. This larvae will consume all the green leaf tissue of bentgrass in a small radius (initially about the size of a quarter).

Look-a-likes — Black cutworm feeding damage looks very similar to ball marks. However, a ball mark won’t have a central hole in the center. Also, a ball mark won’t continue to grow in size and shape (irregular) over time.

Cutworm Image 1. Superintendent, “Looks like ball marks to me.” Me, “I don’t think so. This is mixed in with ball marks but it is different.” Settle, Jul 7, 2021

Cutworm Image 2. See that ‘ball mark’ with a hole in the center. And here’s another. And another.” Superintendent, “I’m going to treat that tomorrow.” Settle, Jul 7, 2021

Nocturnal — It is uncommon to see cutworm larvae feeding during the day and is another reason that the damage can go unnoticed (or is confused with ball marks). They, the larvae, are programmed for survival.

Birds — Foraging birds, often starlings, are good indicator that insect activity is beneath a turfgrass area. When we see birds probing it means they are in search of supper (in this case cutworm pupae and larvae on a green). Many of the best turf managers on the planet will tell you that they watch bird behavior to understand what they might be up against insect-wise. Especially true when it involves greens or tees.

Cultural — There are some alternatives that can be useful for control or suppression of cutworm larvae. Most of these are pretty straight forward. One that caught my eye, frequent mowing, is because we are already doing this on golf greens. So the good news is that we are probably already providing a level of suppression by removing/reducing the number of cutworm eggs (initially placed on leaf blades by the moth). However, this doesn’t provide complete control for greens or tees.

Insecticides — A curative strategy is effective only when combined with regular scouting and identification. Once identified, many insecticides are available (labeled for black cutworms). Follow the label.

The insecticide should be watered-in immediately to the depth of the larvae. This can be easily determined by excavating the hole. Once watered-in, irrigation cycles should be halted for a period of 24 hours to allow for efficacious control within the zone of activity.

Reference — Managing Black Cutworms In Turfgrass, Purdue University https://extension.entm.purdue.edu/publications/E-270/E-270.html