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White grub damage has been showing up over the past several weeks in many areas of the Northeast. I wouldn’t be surprised to find grub activity in areas that were treated earlier in the year with a preventative insecticide because above-average precipitation like we experienced this summer can favor beetle activity and lessen insecticide performance.

However, just because you find a population of grubs below the turf surface doesn’t mean you should automatically load up your sprayer with an insecticide. Late-season treatments, particularly in October, are much less effective. Work from Michigan State University indicates that September treatments result in a 20%-80% kill whereas only 20%-55% when applied in late October. Fully grown white grubs are harder to kill, and it could take as long as 10 to 14 days after treatment before they die. Not to mention, the damage is probably already done.

Trying to promote turf recovery with additional seed and fertilizer is arguably a much better use of resources this late in the year. Save your insecticide until next year and make sure to apply at the appropriate time. For curative treatments with products like carbaryl or trichlorfon, treat prior to May 15. After that date, grubs stop feeding as they prepare to pupate. In general, preventative treatments provide the best solution to grub problems. They include products like imidacloprid, thiamethoxam, clothianidin or chlorantraniloprole. Just make sure to avoid applying too early in the year as the products will degrade over time – leaving your turf susceptible to outbreaks come next fall. Mid-June to early July is typically the best timeframe to apply preventative insecticides for controlling grubs in northern states.

Northeast Region Agronomists:

Adam Moeller, director, Green Section Education –

Darin Bevard, director, Championship Agronomy –

Elliott Dowling, agronomist –

John Daniels, agronomist –

Information on the USGA’s Course Consulting Service

Contact the Green Section Staff