After a very cool spring, the annual bluegrass weevils (ABW) are finally beginning to show up in turf samples from golf courses in southern New England. We are monitoring five sites for the Weevil Trak program, and this week all five of them had several second instars in the turf samples they sent us. Those larvae are the product of egg laying from about two weeks ago. (Incidentally, second instars are tiny and virtually impossible to see in the field because they are well hidden inside the stems. We find them by using a salt flush to draw them out of the stems - and then we have to look at each one under the microscope to see if it has a head capsule!!!)
The numbers in the samples are beginning to rise, suggesting that the adults have finally gotten down to the business of laying eggs, and the numbers undoubtedly will continue to rise. Meanwhile I noticed a rhododendron on campus yesterday whose buds were just beginning to open. (This plant is in full sunlight and so is probably a few days ahead of its cousins in the area, but may be blooming soon.)
What does this mean for your field decisions?
If you are planning to use chlorantraniliprole (Acelepryn™) for ABW control, you should apply it as soon as possible. (It can be a good weevil product, but you should not rely on it as your sole source of control.)
If you are planning to use a product targeting larvae, most of them should be applied when rhododendron is in full bloom. (It is best to use plants on the golf course as your indicator plants, but if you don't happen to have any, keep checking rhododendrons that are close by and growing in comparable conditions.)
Standard larvicide options include spinosad, indoxacarb, and trichlorfon.
Cyantraniliprole (Ference™) has been shown to be effective against adults and larvae, and appears to have a fairly wide window during which you could apply it with good success. It appears to be very effective against larvae, in particular. If you want to use the product to control white grubs as well, I would probably hold off until late June or early July and count on the material to reduce the population of the second generation at the same time as it is positioned to control grubs. But if you are planning to use it primarily as an ABW control option, I would apply it any time in the next two weeks. (The same rhododendron bloom guideline works for cyantraniliprole, and I would not wait any later than full bloom.) That approach should provide very good control of the first generation
Note that some areas in New England have received several inches of rain since early April, while others are on the dry side. If your soils are dry, remember that ABW larval feeding damage may be a little more visible. Sometimes you can mask a little bit of damage by providing adequate moisture to keep the grass growing! (That won't reduce the number of larvae, but it might reduce the damage enough that some of the golfers don't notice it.)
It will be challenging for some of you, as the critical application may fall during or shortly after the upcoming holiday weekend. And it looks like the temperatures will finally reach seasonable levels, which means the larvae will develop quickly in the plants.
Submitted by: Dr. Pat Vittum