Buckle your seat belts, here we go!
Samples sent to us this week from around southern New England have confirmed that ABW larvae are finally hatching and becoming active. After several weeks of seeing only an occasional second instar, this week we saw lots of third instars (the stage that leaves the stem) and even a few fourth instars. And the number of larvae was much higher in most samples than it had been for the previous three or four weeks.
My concern is that the egg-laying period for the ABW was more prolonged than usual this year. (Indeed there undoubtedly are still females laying eggs even now.) That means that instead of having one fairly well defined spike in larval activity in the spring generation (along with a well defined period when the new adults emerge), we will probably experience several weeks during which we see a mix of second, third, fourth, and fifth instars, along with pupae. And THAT means that control of summer weevils will be more difficult to time well, because some adults will emerge by mid June while others may not emerge until mid July. It's hard to achieve good control when so many different stages are present at the same time!
Attached is a graph that shows the accumulated degree days at Tumble Brook Country Club in Bloomfield, CT. As noted in a previous post, the superintendent, Cindy Johnson, has been a Weevil Trak cooperator for eight years, so we have the temperature data from the same location for eight years. April started relatively warm compared to the previous eight years, but then it turned much cooler for a couple weeks, so by the time we got to early May, the degree day accumulation for 2016 was about in the middle for the eight years. By the middle of the month, it was one of the coolest years we had seen.
Current Degree Day Comparison for Tumble Brook CC
But earlier this week we began to experience some notably warmer temperatures (in the mid to high 80s throughout much of the region), and Rhododendron catawbiensis went from just beginning to show some color to full bloom in a span of about three days - especially in sunny areas. We normally consider 325 to 350 degree days to be a good target for applying a larvicide, and that usually coincides pretty closely with Rhododendron full bloom.
Many of you in southern New England are now in that situation - degree days around 325 to 350 and Rhododendron in full bloom. And the forecast calls for continued high temperatures for the next several days, so we will be accumulating 15 to 20 degree days per day. This will translate into rapid development of ABW larvae. It is important to target the larvae as soon as possible, recognizing that there will be some "laggards" that are still in the stem, so you probably will not experience as high levels of control as you have in some years.
For those of you in cooler locations, remember that the warm temperatures will move things along quickly, and you can expect to see the Rhododendron blooming soon.
Many of you should make an application of a product targeting larvae (e.g, cyantraniliprole, indoxacarb, spinosad, or trichlorfon) within the next week. Doesn't it figure - the critical time for application falls smack dab in the middle of Memorial Day week-end.
Submitted by: Dr. Pat Vittum
