You Are Here: Management Updates 2008 Archive June 23, 2008

Date: June 23, 2008
Category: Insects
Subject: Armyworms, Sod Webworms, Black Cutworms

Armyworms
We have had an unconfirmed report of an armyworm (Pseudoletia unipuncta) infestation attacking a low maintenance turf area in the metropolitan Boston area. The report is "unconfirmed" because I have not personally seen samples of the caterpillars, but the report is pretty likely to be accurate because I was able to send digital photos of armyworms to the turf manager and he confirmed that his specimens looked just like my pictures.

An armyworm caterpillar, click to enlarge (Photo by Patricia J. Vittum).

In their medium and larger stages, the caterpillars are very dark (described as black or navy) on the top, with a straw-colored stripe along the side of the body. The head capsule has two shades of brown (dark and light), with a kind of "honey-comb" pattern. And the fleshy legs on the abdomen usually have a dark stripe near where the leg attaches to the body.

Some of you will remember the remarkable infestations that appeared during June 2001 in some parts of southern New England. In that case we believe the armyworms were blown in (while in the moth stage) from New Jersey and other regions south of New England during a large coastal storm early in June. Many turf managers that year reported caterpillar infestations of "biblical proportions" - the caterpillars emerged in incredibly high densities and marched, like an army, across turf areas and pavement, leaving death and destruction in their wake.

We have not yet heard of other reports of armyworms, so I don't know whether this latest report will turn out to be an isolated instance or whether we may see large areas affected like in 2001. If the activity turns out to be more widespread, I offer the following suggestions:

1. If the caterpillars are already nearly full sized (they typically reach 1.25 inch in length during their last instar), there are no chemical or biological control strategies that will provide significant levels of control.
   
   In that case, about the only thing you can do is minimize stress on the turf. Raise the mowing height a bit (to try and increase the photosynthetic surface), which may help the turf a little. And if possible, water the area as needed, again to help the turf through the stress period.
   
   
2. If you notice the caterpillars early enough that they are still small (less than half an inch), you should achieve reasonable levels of control - at least knock the population back to a dull roar. You can use a pyrethroid, carbaryl (Sevin™), or indoxacarb (Provaunt™). In addition, a product containing spinosad (often sold as Conserve™) provides good control of many caterpillars, and while I don't have any data either way, it might also be effective against armyworms.

Sod webworms
I have had an unconfirmed report of sod webworms activity in central Massachusetts (Sterling area). The turf manager reported that webworm moths were flying in the area, and that some turf appeared to be showing damage from caterpillars. While that report is unconfirmed, I went home that evening and noticed that large numbers of webworm moths were flying in my own lawn, so I fully expect that the "diagnosis" was accurate.

In most cases we do not see damage from sod webworms in New England, but it does occasionally happen. There are several species of webworms, each of which produces caterpillars that feed in the turf and can leave straw-like patches of dead grass. Several of the webworm species spend the winter in New England in a late caterpillar stage, feed briefly in the spring, and then pupate and emerge as moths. These are the moths that flit aimlessly, just above the turf, dropping eggs as they go.

Again we normally do not see damage from these insects, but there can be exceptions. If you have reason to believe that the damage your turf incurred a couple weeks ago was caused by webworm caterpillars and you see webworm moths flying now, consider applying a pyrethroid in the area about a week or two after peak moth flight. That gives the moths time to produce and lay eggs, and the eggs to hatch into tiny caterpillars. Water very lightly, just enough to knock the material off the blades and into the thatch.

Black cutworms
And finally, I have had reports from a couple of golf course superintendents of black cutworm activity on greens, tees, or fairways. (Black cutworms usually are strictly a golf course problem.) So now would be a good time to check for damage in the usual places. Are those ball marks on the greens really ball marks???

Submitted by: Dr. Pat Vittum

DISCLAIMER - As always, it is the responsibility of the applicator to verify the registration status of any pesticide BEFORE applying it. Different states have different regulations as well. The author and the University of Massachusetts are not liable for any consequences of any pesticide "recommendations". Mention of any trade name is not to be considered endorsement of a product.

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