When to put down grubex

Asked March 21, 2020, 10:15 AM EDT

Last fall I discovered I had a bad infestation of grubs and asked for advice from you. You told me to put down grub ex in the spring. Based on our weather this year, can you tell me the best time to manage this? What ground temperature is optimal for grubs? Any help is appreciated. Thanks!

Harford County Maryland

4 Responses

Make sure you have a grub problem.
Reasons to apply a grub control include - a past history of grubs, if you have a sprinkler system that keeps the soil moist for egg laying, and if we have weather conditions like wet summers and lush lawns while the adult beetles are active in June. It is normal and not problematic to have a few grubs in the soil (in fact, helpful because it keeps the grub predators around.) Unless you are seeing around 10 per square foot, and your lawn suffered severe damage last fall, it does not warrant the expense and impact of spreading any pesticides.

In general, adult egg laying begins in July and root feeding begins in August.
Grub controls are applied as a preventative. Look for a season long grub control that contains the active ingredient Chlorantraniliprole. This product is more environmentally friendly and has a broad application window (May through September) not now. Read and follow label directions.


Thanks for,your response, but I’m not sure I understand. I definitely have a grub problem. Last fall, large swatches of grass “rolled up” when I was thatching. I had about 20 grubs in a 1 ft section and this was late fall. I was told it was to late to put something down and to wait till spring. I’ve reseeded the yard and need to know when to put down grubex for the grubs that are there from last year. Would that be early June, late May, or early May? I don’t want my new grass to be eaten. What is the soil temperature that encourages grubs to emerge? Thank you for your help.

Or would that be July or August? Sorry,

In late March or early April, grubs return to the surface and briefly feed on roots. In the spring, grass is putting out new roots and growing vigorously. Grubs are not as bad a problem in the spring and they are not feeding that long.
Although grubs feed throughout the growing season, their damage is only severe in late summer. No control is needed now.
Put down a preventative season long grub killer in late June as in Grubex. Follow label directions for application. See more on japanese beetles https://extension.umd.edu/sites/extension.umd.edu/files/_docs/programs/hgic/HGIC_Pubs/Insect_pests/HG78%20Japanese%20Beetle_2018.pdf