You Are Here: Management Updates 2008 Archive April 18, 2008

Date: April 18, 2008
Category: Insects
Subject: Annual Bluegrass (Hyperodes) Weevil, Neonicotinoids for Spring Grubs

Annual bluegrass weevils on the move:
Right on schedule, the annual bluegrass weevils (a.k.a. Hyperodes weevils) are beginning to move throughout New England. We have had reports of adults moving on the greens and tees along the Connecticut shore, and I have no doubt they are moving in Westchester County and Fairfield County as well. (I assume they are already active on Long Island!) So they should be showing up soon in Hartford County, and in much of southern Massachusetts a few days after that.

Remember that most traditional spring applications (a pyrethroid or chlorpyrifos) that are made targeting adults should not be made until Forsythia is showing some leaves along with the flower blossoms (what I call "half green, half gold"). In some years the applications that are made at Forsythia full bloom work fine, but in several years we have seen drop offs in performance of the products - presumably in part because cold snaps intervene and slow down weevil development.

So try to avoid the temptation to go as soon as you see bright gold Forsythia.

A follow up on spring applications of neonicotinoids:
Apparently several people have wondered about some comments I made in an update earlier this week regarding the use of neonicotinoid products in the spring for white grub control. I indicated that spring (meaning April or early May) applications of neonicotinoids probably would not reduce populations of white grubs already present in the turf. I based those remarks on field trials that were conducted several years ago using imidacloprid (Merit™ and several other trade names now).

Imidacloprid was the first neonicotinoid to reach the turf market (more than 10 years ago). More recently chlothianidin (available as Arena or in a combination product with bifenthin, sold as Aloft™) and thiamethoxam (Meridian™) have been registered in the turf market. Both of these active ingredients are more soluble than imidacloprid and appear to be effective against a wider range of insect species.

I have talked with a few of my turf entomology colleagues who conduct many of the field trials that we all use to develop our recommendations. Neither of them has conducted any trials where a neonicotinoid (whether imidacloprid, chlothianidin, or thiamethoxam) has been applied in the spring to target grubs that are present in the spring. Neither have I. So at this point there appear to be no data to confirm whether spring applications will control spring grubs. I have always been a "show me" sort of person, so without data to back up a recommendation, I am reluctant to suggest treatment strategies that have not been tested.

However, studies conducted in Ohio involving September applications targeting large grubs showed that chlothianidin reduced grub populations quickly (about a week), while thiamethoxam reduced grub populations in about seven to 10 days, and imidacloprid took at least two weeks to achieve grub reduction. (We conducted a smaller scale test in September a couple years ago that yielded very similar results against oriental beetles.) It is tempting to extrapolate from those autumn field trials to project that spring applications of chlothianidin or thiamethoxam could control spring grubs, but the appropriate field studies apparently have not been "commissioned" by any of the companies. Certainly I have not conducted those trials, and neither have three of my trusted colleagues. Keep in mind that spring grubs are different, physiologically, than they were in the previous fall. While they feed some in the spring, they are also beginning to prepare to pupate, so they may be a little less susceptible to chemical control. Certainly the "success" rate with fast acting products like trichlorfon (Dylox™) in the spring is usually quite a bit lower than it is when applied the previous late summer or fall.

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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