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Management Updates

This section of the web site features Management Updates written by the turf specialists of the UMass Extension Turf Program. The messages cover regional problems, are geared toward regional conditions, and are posted frequently during the growing season.

The most current message appears below; click into the archive to messages from the current and previous growing seasons.

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White Grubs

Aug 19 2015

NOW is a good time to monitor for white grub activity!!!

We were scouting for grubs at a local golf course last week and found populations (mixed oriental beetle and Japanese beetle) of 20 grubs or more per square foot in untreated roughs. At that point about 60% of the grubs were second instars, and the other 40% were first instars. But with the recent warm weather, the grubs are undoubtedly developing quickly, so by early next week, most of them should be second instars or early third instars.

Because of the timely rain that has occurred throughout the summer in many parts of New England, beetles have been laying eggs at the "normal" time. European chafer females started laying eggs in late June, while oriental beetles and Japanese beetles started laying eggs around the second week of July in much of western Massachusetts.

As noted above, the grubs that emerged from these eggs are developing quickly. So this would be an excellent time to get out there and take a close look at some of your typical trouble spots. You can use a small spade to cut a hole about 4 to 6 inches on a side, and use a hand trowel to dislodge the soil from the sample. Any grubs will pop out of the soil quite easily, and while they are still relatively small (0.25 inch long), their cream color contrasts well with the dark soil. We use a golf course cup cutter to remove our soil samples - the core is about 0.1 square foot, so it makes the calculation of population density very easy. At this time of year, you only need to dig down about two inches. The grubs are up high in the root zone.

Remember that the tolerance level for white grubs in unstressed turf is around 8 to 14 grubs per square foot for Japanese beetles and oriental beetles, a little lower for European chafers. Also remember that any turf areas that have not received timely rainfall and are not irrigated may experience a delay in egg laying. (Females often delay egg laying when soil moistures are too low for the eggs to survive.) So in these situations, the grubs that are present may be a little smaller.

Finally, it is getting late to apply imidacloprid, in my humble opinion, and it is too late to get good control with chlorantraniliprole. But several colleagues have conducted trials with a related compound, cyantraniliprole, and it appears to work more quickly than chlorantraniliprole, so it might provide some relief. Chlothianidin, whether as a stand-alone product or in a combination with a pyrethroid, works more quickly than imidacloprid and should provide very good control if applied in the next two weeks. And of course there is the traditional curative product, trichlorfon, which will work very quickly (but won't stay around very long) - for those who can use it. Trichlorfon cannot be used on school grounds in Massachusetts and several other northeastern states.

Submitted by: Dr. Pat Vittum

For additional information about integrated management of turf pests, refer to our Professional Guide for IPM in Turf.