UMass Extension Turf Program

Armyworms, Annual Bluegrass Weevils, White Grubs

June 7, 2012
Armyworms, Annual Bluegrass Weevils, White Grubs

Armyworm alert

Armyworm close-upAbout a month ago I saw a note from Indiana reporting outbreaks of the true (common) armyworm, Pseudoletia unipuncta. There was also mention of some activity in Ohio about two weeks ago, but I had not heard of any outbreaks further east until today, when we received an update from the Cornell IPM program. Apparently several sweet corn fields in central and western New York have been attacked by armyworms, with at least one field suffering total loss.

For those of you who remember the outbreak in Massachusetts about 10 years ago, this may strike some fear in your hearts. Armyworms feed on corn and several grains (especially wheat and rye). But they also can attack managed turf, and when they do so, they move across the area like an army, moving from areas they have destroyed to areas with plenty of food. Many turf areas, including golf course roughs, lawns, cemeteries, parks, and athletic fields, sustained damage in the most recent outbreak in Massachusetts.

Be watching for armyworm caterpillars in the next couple weeks. Sometimes the moths arrive on weather fronts, and sometimes they are blown passively from one place to another. The females lay eggs at night, often in clusters of about 120 to 140 eggs per cluster. Each female can produce up to 2,000 eggs, so it does not take very many females to produce a damaging population of caterpillars.

It is very difficult to control armyworms once they reach their full size (about an inch), so monitor likely spots and watch for small caterpillars. Sometimes the smaller caterpillars will be a light green with light colored stripes on each side. The large caterpillars tend to be very dark (often described as a very deep navy or black), with a light colored stripe on the side of the body below the spiracles.

If you observe caterpillar activity when they are still small (less than a half inch), you may get some relief with the usual caterpillar products, including spinosad, indoxacarb, chlorantraniliprole, or a pyrethroid. (Remember that in most cases, chlorantraniliprole should already have been applied if you are planning to use it for grub control.)

Annual bluegrass weevil

Annual bluegrass weevils in many areas in southern New England are now prepupae (which look like larvae but are done feeding), pupae, or young adults. So the worst is over for now in those locations. Golf courses in central or northern New England are still dealing with larvae feeding, so continue to monitor the usual hot spots.

White grubs

We were collecting samples from one of our grub sites on Tuesday, and found that most of the individuals were already pupating. This site is predominantly oriental beetle, and oriental beetles often emerge just a few days before Japanese beetles, but the point is that we will be seeing adults of oriental beetles within a few days, with Japanese beetles "popping" soon after that. While I have not had reports of European chafer adults flying, I have to believe that they are already flying in the usual hot spots. (They are nocturnal but you might notice clusters of beetles in the branches of various trees, especially ones that are silhouetted against the western sky in the evening.)

Submitted by: Dr. Pat Vittum


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