You Are Here: Management Updates 2006 Archive April 18, 2006

Date: April 18, 2006
Category: Insects
Subject: Annual Bluegrass (Hyperodes) Weevil

We spent Patriots Day in Westchester County checking out annual bluegrass weevil sites. We will be processing several turf samples later today and Wednesday to see where the adults are right now. Some superintendents have reported seeing adults "out and about" while mowing.

Forsythia are in bloom in much of southern New England now, and I am getting many questions about whether it is time to apply an insecticide. I repeat my cautions of previous years - HOLD OFF until you see at least some green leaves forming on those Forsythia. And note that there are different varieties of Forsythia, some of which bloom earlier than others. Meanwhile on some golf courses there may be a difference of a week or more in blooming dates from one part of the course to another.

So for many, even in Westchester County, it is still a little too early to make your application against the adults.

There have been some "rumblings" about resistance. Have the annual bluegrass weevils developed resistance to pyrethroids??? Last summer a colleague (Rich Cowles, Agricultural Experiment Station, Windsor, CT) conducted some quick tests with weevils collected from golf courses in the Hartford area. He put measured amounts of a pyrethroid on filter paper in a petri dish and released adults in the dish. He then observed the weevils and recorded their survival rate. That survival rate was much higher in the "treated" dishes than he would have expected, based on the doses he was using. That could be an indication that some weevil populations were developing resistance to the chemical. So he reported those results informally, in an effort to help superintendents refine their management strategies.

As far as I know, these experiments have not been duplicated, so I am not in a position to know whether or not resistance is occurring or whether it is widespread. There are several ways to conduct experiments to measure the dose necessary to kill insects, and we hope to conduct trials later this year using at least one of those techniques to get a more complete picture of the situation. But I can say that we had a field trial at one of the golf courses where Dr. Cowles collected weevils later in the summer, and flowable Talstar™ (bifenthrin) provided more than 75% control in that trial. (Our field trial was a traditional one, where insecticide was applied shortly after Forsythia hit the "half green - half gold" stage, and we collected our samples in early June to count larvae. Dr. Cowles collected weevils from the same course a few weeks later.) Ordinarily I would consider 75% control to be slightly below what we are seeking but not an indication that resistance is a problem. So the bottom line is - we really don't know where or whether we have widespread resistance issues with the annual bluegrass weevil.

I believe Dr. Cowles plans to continue his studies this year, and my lab will be investigating other methods of screening for resistance. And certainly the potential is there - many different kinds of insects have developed resistance to pyrethroids over the last 20 years. So common sense dictates that we do anything we can to minimize our reliance on pyrethroids. I'll cover some of those alternatives next week, but for the short term, look into minimizing the annual bluegrass or at least minimizing the stress on the Poa. Easy for me to say, not so easy for you to do! But can you skip a cleanup pass every now and then? Can you develop a long-term plan to minimize annual bluegrass? Can we figure out ways to make it more difficult for the adults to move from their overwintering sites back to the short-cut grass?

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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