June 28/11. We are reporting very high numbers of black cutworm moths in traps right now. These numbers are, in fact, higher than we have seen in many years.
What this means to you is that there is a possibility that these moths will lay eggs on your turf and the resulting caterpillars may damage your golf course.
We generally do not see black cutworms damage fairways although we know they are feeding there. On bentgrasses, however, damage can become quite severe if populations are high and feeding goes undetected.
We are not suggesting preventative treatments because of the spotty infestations of these insects, but we are suggesting that you be aware of the increased threat right now and monitor bentgrass tees and greens for the presence of the caterpillars.
Larvae are hairless caterpillars with unique markings on the head and body. The upper half of the body is a darker gray than the lower half.
They have black dots along both sides of their body.
Newly hatched cutworms are small but they may grow to a length of 2 inches.
A soap solution (1/2 ounce of liquid dish soap per 3 gallons of water) applied as a drench to the green during the day will flush the caterpillars from below the thatch to the surface where they can be easily seen. If three or more cutworms per square yard are found, a pesticide application may be needed.
If a decision to treat a green or tee is made, remember to also treat a 20-foot border to kill any cutworms that otherwise may crawl onto the green. Research from Wisconsin shows that daily mowing may remove more than 75% of the cutworm eggs before they hatch. However, eggs easily survive the mowing and may hatch where the grass clippings are deposited. It is therefore recommended that clippings be deposited at least 100 yards from susceptible tees or greens to prevent the cutworms from crawling back.
One female black cutworm moth can lay up to 2,000 eggs over a series of several days. The eggs hatch in three to 10 days (depending on temperature) and the young caterpillars begin to feed on the grass shoots. As the caterpillars increase in size, they burrow into the turf and move to and from these holes at night to feed on the grass.
Regular sampling for cutworms and damage, followed by insecticide treatment, if needed, will protect turf grass against significant damage by black cutworms. Chemical control should only be considered when the cutworms are confirmed in high numbers and damage begins to become apparent.
Insecticides recommended for cutworm control include any of the pyrethroids labeled for use in turf.
Tim Gibb, Turfgrass Entomologist
