You Are Here: Management Updates 2004 Archive June 4, 2004

Date: June 4, 2004
Category: Insects
Subject: Annual Bluegrass (Hyperodes) Weevil Update

Hyperodes weevils (a.k.a. annual bluegrass weevils) are causing headaches for golf course superintendents up and down the Atlantic seaboard - and even into western Pennsylvania. We have had reports (unconfirmed but numerous!) of weevil damage in the Philadelphia area, south Jersey, and West Virginia, as well as western Pennsylvania and many locations in New England.

We just analyzed samples from Westchester County, NY, earlier today. Samples were taken fromplots that had about 150 larvae per square foot last week, and the larvae had been evenly distributed at that time - small, medium, and large larvae. I had expected to see a lot of pupae in today's samples, but was surprised to continue to see lots of small larvae, along with medium-sized larvae and large larvae. There were a few pupae, but not as many as I had expected.

Here's what I think is going on: First of all, something about the conditions this past winter and early spring was very favorable for weevil survival, so populations are higher than we have seen in a long time - at least in many locations. Obviously, the adults survived the winter very well.

The spring temperatures were variable, with stretches of warm weather followed by cooler conditions. It appears that some adults got an early start and began laying eggs about "on schedule", while others were delayed. As a result, we had a very extended period of egg laying in most locations. This means we are already finding all sizes of larvae and pupae in the same site. While we often see overlap later in the season, it is a little unusual to see such a spread this early in the summer.

The practical implication of this spread of development is that it will be very difficult to figure out the most efficient way to control weevils this year. It will be more important than ever to scout the property and know what stages you have in a given area. Larvae look like grains of rice with brown heads. Pupae are cream colored and sort of diamond-shaped, and you can see the wings developing on the back. Collect turf cores and tease apart the turf by hand, looking for larvae or pupae in the thatch and crowns of the plants.

If you collect samples and find that more than half the insects are still in the larval stages, you may get some relief by applying a fast-acting insecticide that does not get tied up in the thatch. (Note that the various pyrethroids generally are NOT effective against the larvae.) If more than half the insects are already pupae, it probably will NOT pay to treat. Pupae will not feed nor will they cause additional damage. And remember, pupae are not susceptible to control anyway. If most of the insects are already pupae, chances are many of the larvae are also almost done feeding.

If you have noticed that most of the insects in the thatch or crown are pupae, you may want to wait about a week and then consider applying something that stays in the thatch. This application will be targeting the new adults as they begin to emerge. (Some of you, especially in the Philadelphia area, may have already seen the new young adults wandering on the surface of the putting greens or collars or tees. Young adults are red-brown but otherwise look just like the black adults you have seen in the textbooks.) In this case, the pyrethroids are an excellent choice.

Ordinarily an insecticide application targeting the new adults is made in late June or early July in the metropolitan area, but it appears we will be at least a week ahead of that schedule this year.

We will continue to post updates on weevil development as we learn of it. Samples from near Hartford, collected earlier this week, revealed mostly large larvae. So the weevils are on the move, and superintendents throughout New England should start seeing the tell-tale wilting symptoms in the next few days, if they have not already.

- Submitted by: Dr. Pat Vittum