Annual bluegrass weevil larvae on the move in New England
We have been processing the samples from one of our field trials this week (pulled the samples on 7 June), and have noticed some things that are a little unusual relative to annual bluegrass weevil larval activity. Normally we see much more activity (and damage) from larvae feeding along the edge of a fairway in the spring, while the middle of the fairway is relatively unscathed. Many people have claimed that adults leave the fairways in the fall and move to more protected sites (rough, tree lines), and then walk back to the fairways in the spring. That would explain why we usually see more severe damage along the edges of the fairways in the spring. (Subsequent activity may occur anywhere on the short grass, because the weevils that emerge from the first generation are already "there".)
But this year in one of our trials, we found moderate populations in the untreated plots along the edge of the fairway, but we found fairly high populations in an untreated plot that was 25 feet into the fairway from the rough. This observation matches that of some of the Syngenta personnel, who were visiting golf courses in upstate New York and Vermont earlier this week. I have also received e-mails from some superintendents over the past two days, suggesting that this phenomenon is occurring in several places in New England this year.
Many of my colleagues have long suspected that some individual adults overwinter in the rough, not moving to more protected sites (e.g., in leaf litter under trees), and might even overwinter in the fairways, particularly during miild winters. My guess is that the mild winter conditions that we experienced this year may have enabled weevils that did not leave the fairways last fall to survive on the fairways just fine. That means they would have been more likely to move further into the fairway earlier in the growing season than we usually see. And that means they would have been available to lay eggs further into the fairway than normal.
This may be bad news for people who just "ring the fairway" in the spring. Most years a perimeter spray provides very good protection against larval damage in the first generation, but this year we may see some unpleasant surprises on courses that only protected the perimeters and did not apply larvicides to the middle of the fairways. So be really vigilant in the next few days and monitor for larval activity very aggressively.
The cooler temperatures that are forecast for much of New England for the next several days will provide some help by minimizing the stress on the Poa annua, but we are also not expecting much rainfall in the next few days. So areas that are prone to drying out may be under additional stress from the unseen larvae. Get down and take a look. If you see lots of large larvae (and especially if you see pupae), it may be too late to apply an insecticide - but you can help the turf get through the stress by providing adequate water to support the root system. If you see lots of medium-sized larvae (more likely to be active in the thatch rather than the upper root zone), you may get some relief by applying a larvicide. Cyantraniliprole appears to have fairly good activity against medium and large larvae.
Submitted by: Dr. Pat Vittum