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Management Updates: Jun 7, 2016

White Grubs, Annual Bluegrass Weevils
Jun 7, 2016

White Grubs

When I got home from a meeting the other night, I noticed several scarab beetles that had been attracted to the lights on the outside wall of the house. They looked like European chafers but it seemed a little early so I took a close look at the tips of the beetles' feet and noticed that these beetles had a little projection on the tip of the tarsal claw. That means the beetles were NOT European chafers, but they are one of the species of May/June beetle (in the genus Phyllophaga). There are several species of Phyllophaga in New England, and most of them take two or three years to complete a generation.

I expect to start seeing European chafer adults flying at twilight any time in the next couple weeks. (Often the adult emergence begins to increase markedly around the middle of June but because this spring has been a little cooler than many of our recent springs, that emergence might be delayed a little bit. Meanwhile I also expect to start seeing oriental beetles flying within the next couple weeks. Japanese beetles will probably become noticeable pretty close to their "normal" emergence time of July 4th.

If you are planning to use a neonicotinoid as a preventive application to control white grubs, remember that the ideal time to apply is "when the beetles are laying eggs". Normally it takes a week or two after the adults emerge before they become reproductively mature, and usually there is a period of two or three weeks during which adults begin to emerge. If you are in an area with mostly European chafers, the ideal timing would be the last week of June through the third week of July. If you are dealing mostly with Japanese beetles or oriental beetles, my opinion is that your ideal timing for application would be the second week of July through the first week of August.

Annual bluegrass weevils

As we have been reporting all along, the first generation this year is much less well synchronized than we often see. In fact, last week we saw a tiny larvae (second instar), medium and large larvae, and a pupa, all from one 2-inch diameter plug! When the population is synchronized, a large portion of the insects passes through the fifth instar at the same time, which means we often see discrete periods where damage is visible. And then the second generation is at least somewhat synchronized.

We are reading samples from a golf course near Boston even as I type this update on Tuesday, 7 June. Six of the small cores have at least one third instar, one fourth instar, one fifth instar, and one prepupa (which looks like a larva but is done feeding and will become a pupa within the next two days). So we have a very spread out distribution this spring. This means that we probably won't see a clear peak of large larvae.

The good news is that we are less likely to see areas with severe damage because only about a third of the individuals will be in that most damaging fifth instar at any given time. But if the weather turns hot and dry, areas that have been weakened by larval feeding will fail quickly. The bad news is that it will be VERY difficult to time applications to control the second generation this year, because the population will always be a mixed bag of small larvae, large larvae, pupae, and adults. We don't have any silver bullets to handle such a challenge. Cyantraniliprole is looking very promising against small and large larvae, and may have activity against adults as well, but we cannot expect it to solve all of our problems - and we must be careful not to overuse it.

Submitted by: Dr. Pat Vittum