Should you treat?
If your grub counts exceed the damage thresholds, you might want to consider treating for them. Your decisions will depend on when you find the grubs. If treating, target only the areas where grub populations exceed the suggested thresholds, or where you’ve had a bad history of grubs.
For information on identifying white grubs, see What Do White Grubs Look Like?
|Number of grubs per|
|Asiatic garden beetle||18-20||2|
|Black turfgrass ataenius||30-50||3-5|
|Green June beetle||5||Any|
|Northern masked chafer||8-12||Any|
|May and June beetle||3-4||Any|
|14.25-inch diameter soil core of the standard golf course cup cutter|
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.
In August: The grubs are still small and have not caused a lot of damage yet, and are more susceptible to insecticides. In New York State you could apply beneficial nematodes, imidacloprid (Merit), or trichlorfon (e.g., Dylox), listed from least to most toxic. Note that on Long Island, imidacloprid may only be used if applied by a certified pesticide applicator. In other states, additional products may also be available.
In September: It’s too late to use most products. Beneficial nematodes or trichlorfon may be used.
In October: It’s really too late to treat this year’s population. Treating them is a waste of time and money. Focus on compensating for grub damage.
Compensating for grub damage
You can help your lawn to compensate for loss of roots by watering it regularly, providing good fertility, and reseeding damaged areas—actions that will improve any lawn’s looks, too.
Cornell research shows that fall fertilization (0.25-5 lb. of N per 1,000 square feet) enhances turf recovery from grub damage. Check to see if there are regional fertilizer restrictions for your region.
Disclaimer: For the most up-to-date information on insecticides approved for use in New York State, see the Cornell Guide for Commercial Turfgrass Management. To calculate the environmental impact of different pesticides, visit A Method to Measure the Environmental Impact of Pesticides.
Read pesticide labels prior to use. The information contained here is not a substitute for a pesticide label. Trade names used herein are for convenience only; no endorsement of products is intended, nor is criticism of unnamed products implied. Laws and labels change. It is your responsibility to use pesticides legally.