You Are Here: Management Updates 2005 Archive August 24, 2005

Date: August 24, 2005
Category: Insects
Subject: Annual Bluegrass (Hyperodes) Weevil - Resistant to pyrethroids or not?

As I mentioned in an update last week, several superintendents have been suspecting for some time that their annual bluegrass weevil populations had developed resistance to pyrethroid insecticides. This would include such things as bifenthrin (Talstar™), cyfluthrin (Tempo™), lambda-cyhalothrin (Battle™ or Scimitar™), and deltamethrin (Deltagard™). Several people suggested that they had been using pyrethroids this year and not seeing the level of control to which they had been accustomed. It was hard for us to tell, because everybody's populations seemed incredibly high this year. We assumed it was because of the unusual weather patterns we experienced.

Well, my colleague, Dr. Rich Cowles (at the Connecticut Agricultural Experiment Station in Windsor, CT) set up a quick field test to check the susceptibility of adult weevils collected from two golf courses near Hartford, and confirmed that the weevils on those courses had developed a measurable degree of resistance to cyhalothrin. When Dr. Cowles exposed the weevils to the regular rate (1X), as well as 2X, 4X, and 8X exposures, he found the little devils survived even the highest exposure.

He hastens to add that the field test was a "quick and dirty" test, but it provides enough evidence that he wants to continue looking at the matter. He and I hope to collaborate over the next several months to determine the extent of the resistance - in other cases, is it limited to a small area near Hartford or is it scattered throughout the Northeast? And we hope to work with other colleagues as well to begin to develop some suggestions for superintendents for "life after pyrethroids".

Dr. Cowles has offered to provide a little field kit to any superintendent who wants to test his or her own populations to determine whether they might be resistant to pyrethroids. Please understand that this field kit will only provide a brief glimpse, but should provide a quick answer to many people. (Some will be unlucky and get inconclusive results.) If you are interested, please e-mail Dr. Cowles directly at richard.cowles@po.state.ct.us. He will send you some filter paper that has been prepared for the test. You will need to collect 60 to 80 weevil adults and put some of them in a resealable plastic bag with the filter paper, while you put the rest in a separate bag without filter paper. Please be patient - it is possible that Dr. Cowles will be overwhelmed by requests so he may not be able to fill all the requests immediately!

In hindsight, it is not surprising that we have some weevils that have developed resistance. The chemistry of the pyrethroids is such that many different species of insects have developed resistance once they have been exposed through several generations. In recent years many golf course superintendents have relied on pyrethroids to manage annual bluegrass weevils because there were few other alternatives. So we have unwittingly created this situation.

In the short term, the worst should be over for 2005 for almost all of you in the Northeast. With the welcome break in the weather, turf is better able to handle the stress of any ABW larvae that may be feeding now. Within two to four weeks, most populations should be winding down for the year and we will see fewer and fewer larvae. So for now, keep an eye on things and manage the damage as needed. However, for 2006 we will have to be much more creative!

Just because resistance has been found in some populations, it does not necessarily mean that every golf course has resistant weevils. So don't panic - at least, not yet!

Finally - Dr. Cowles would love to find a source of weevils that have not been exposed to pyrethroids heavily over the last three or four years. This would enable him to determine what the "base line" for ABW adults is for pyrethroids. (In other words, how low a dose works on those weevils. He would compare that dose to what it is taking to kill the "resistant" weevils and get a measure of the degree of resistance.) So if anyone has a population of ABW and has not used pyrethroids much (say, no more than once a year for the past three years), please contact Dr. Cowles or me. Thanks!!!

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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