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Management Updates: May 11, 2016

Where Are the Weevils?
May 11, 2016

This spring is shaping up to be a really strange one in the annual bluegrass weevil world. Normally we would be seeing second and third instars in some locations by now (based on calendar dates), but the prolonged cool temperatures appear to be slowing things down a bit. My concern is that the conditions may also greatly extend the period during which females are laying eggs, which will make it even more difficult than usual to achieve good control of the first generation.

We are monitoring six sites for Weevil Trak this year (Tumble Brook CC in Bloomfield, CT; Ludlow CC in Ludlow, MA; Oak Hill CC in Fitchburg, MA; The Country Club in Brookline, MA; Oyster Harbor in Osterville, MA; and Wolfert's Roost in Albany, NY). So far we have only seen a few first and second instars at Tumble Brook and The Country Club, with no activity at the other sites. This has us confused because in past years the weevils have usually shown up first at the site in Albany, but so far we are not seeing any activity there. (His sample site is on a south-facing slope and warms up quite quickly in the spring.)

And normally we will find several larvae per square foot in our samples, but so far the numbers we are recovering from our salt floats are very low.

Meanwhile the adults we have collected from our vacuum sampling have been quite slow to develop reproductively. Only half of the adults collected from a fairway last week in Bloomfield were reproductively mature, and the adults in the rough were even less well developed. Samples from the same site taken yesterday have revealed that most of the adults in the rough are still a long way from being mature. (The superintendent applied an adulticide to that fairway last week and was very successful, so there were not enough weevils for us to dissect from yesterday's collection.)

Right now it looks like the weevils are developing at least a week or two later than last year. It is still too early to tell whether larval populations will be larger than normal or about the same as we usually see. There certainly is evidence that the adults survived the winter in large numbers, and many of them may have overwintered in the rough rather than going to tree lines. But the numbers we are seeing in our turf samples so far this spring are unusually low.

Don't let your guard down. In areas where dogwood (Cornus florida) is still in full bloom, you may still achieve good success with an application targeting adults if you haven't already done so. Monitor your sites carefully and be prepared to apply a larvicide once the Rhododendron catawbiensis reaches full bloom. With the warmer temperatures forecast for the coming days, we will start to see degree days accumulating more quickly.

Submitted by: Dr. Pat Vittum