I have had "conversations" (i.e., e-mail exchanges) with several golf course superintendents in the New Jersey / southeastern Pennsylvania area over the past week. Several astute observers in that region have noticed that annual bluegrass weevil (ABW) larvae have been feeding actively in several areas of the golf course. In some cases they appear to be feeding on creeping bentgrass.
Normally we see damage primarily along the edges of greens, tees, or fairways in the spring, and usually the damage is much more severe in the Poa annua areas than in other turf species. (We assume this is because the edges of the turf areas are under more stress, perhaps from repeated cleanup passes and extra compaction. And the weevil has consistently shown a preference, in lab and field studies, for Poa annua). As the season progresses, the weevil damage becomes more apparent further into the middles of the turf areas. Some sampling studies indicated that larval populations were fairly evenly distributed across a fairway in the spring, but the damage was most noticeable on the edge. Meanwhile several field trials that have been conducted over the years suggest that there are higher numbers of larvae in plots right along the edge of a fairway, at least with the first generation of larvae (June).
Anyway, the reports from New Jersey and Pennsylvania confirm observations that Nikki Rothwell made about five years ago. She was working on a Ph. D. under my direction and spent a lot of time watching weevils. She confirmed that they do, on occasion, feed on creeping bentgrass. I still believe that, given a choice, they normally prefer to feed on annual bluegrass, but they definitely do
sometimes cause damage on creeping bentgrass stands. I have never observed them feeding on perennial ryegrass in the field, but we often raise weevils in the laboratory by providing them with non-endophytic perennial ryegrass so the potential certainly is there. (A close cousin, the Argentine stem weevil, is a major pest of perennial ryegrass pastures in New Zealand.)
Given the forecast for warm weather and, at least in New England, perhaps a break in the constant run of heavy rain, the next couple weeks may be very challenging for golf course superintendents in the Mid Atlantic region up through New England. If the turf looks wilted or does not respond to water, take the time to take a few quick samples and see what is going on. Even in areas that are predominantly creeping bentgrass, there may be significant numbers of ABW feeding. So don't let your guard down yet! If you see large numbers of larvae, you might consider trying to knock them down with trichlorfon (Dylox™) or indoxacarb (Provaunt™).
The good news is that the worst should be over for most of you. In most sites where we have been sampling, populations were much heavier in the spring (May and June), and are considerably lower already. So if we do get a break in the weather, the next generation of larvae should occur at a time when the turf is under less stress and is more able to withstand the pressure.
Submitted by: Dr. Pat Vittum