How many grubs are too many? Research in upstate New York has shown that only 20 percent of home lawns and golf course fairways require treatment. Here’s a guide to treatment thresholds for European chafers, Japanese beetles, and Oriental beetles, the most common grubs in home lawns in New York State. Numbers are based on grubs/sq.ft.
0-5 grubs:
rest easy Fewer than five grubs per square foot is a low population. You don’t need to treat.
6-9 grubs:
think about your lawn Is your grass dense, with a healthy, robust root system, and can you irrigate? If so, it can probably withstand grub populations of 6-8 per square foot, or more. On the other hand, if animals such as skunks, raccoons, birds, and moles are digging up the turf to feed on the grubs and this bothers you, consider treating highly populated areas.
10 or more:
They may cause damage Ten or more grubs per square foot will likely cause damage, especially if the lawn is otherwise stressed. In most circumstances, you’d be justified treating where populations are this high. Several weeks after treating, sample in a few locations to determine whether treatments were effective
The Grub-damaged Lawn
Severe grub damage in a lawn appears as large, irregular sections of brown turf that detach from the soil without effort. Unlike turf damaged by drought or excessive fertilizer, the turf peels away like a carpet being rolled up, because most of the roots are gone.
For most of the year, however, grubs are out of sight and out of mind. They feed on grass roots in your lawn and are usually noticed only when dead and damaged areas appear.
Grubs found in May-July
If you’ve had a history of high grub populations and damage on your lawn, you may want to protect your lawn for the upcoming generation by applying a preventative insecticide. These can be applied most any time from May-July, and for New Yorkers include imidacloprid (e.g., Merit) and chlorantraniliprole (Acelepryn). Long Islanders must note that imidacloprid may only be applied by a certified pesticide applicator and they may not use chlorantraniliprole or clothianidin.
Find Your Problem Areas
You can prevent losses by locating high grub populations before they cause damage.
When to sample
Seek out grubs in early August on Long Island and in mid-August upstate. Sampling early in a grub’s life cycle means that you’ll catch grubs while they are small and less capable of seriously damaging your lawn.
Where to sample
Begin by sketching a simple map of your property, such as the one shown here. Now think of areas that are important to you from a visual or aesthetic standpoint. The front lawn, where visitors enter? Near the back patio? Mark these high-priority areas with Xs that translate to about 10 feet apart. These will be your sampling sites. Consider areas with a history of grub damage and mark these areas, too. Mark low-priority areas with Xs every 20–30 feet. You probably won’t need to sample or treat remaining areas.
Mount your map on a clipboard, grab a full watering can, a piece of cardboard, and either a cup cutter, bulb planter or a shovel, and go to one of the sampling sites marked on your map.
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