Japanese Beetle grubs

Asked March 4, 2016, 11:47 AM EST

We live in Arapahoe County. Our lawn and bushes were attacked by Japanese Beetles last year. When is the best time to treat our lawn to control Japanese beetle grubs? Is now, early March, a good time to put the insecticide on the lawn? Thank you for your help and advice. Becky Clemons

Arapahoe County Colorado lawns and turf

1 Response

Chemical controls for Japanese Beetle (JB) are best applied at the egg laying stage in late May to late July. Controls are less effective later in the season when the grubs are larger, and completely ineffectual when temperatures are cold, the ground is frozen and they are deep within the soil.

For lawns, if possible, limiting water during the period when eggs are being laid and early stage larvae are present (June-July) can be useful in JB control. Egg laying will be concentrated in sites where soil moisture is highest and turf growth most lush.

For shrubs, a common control for adults in the summer is to pick them from plants in the mornings and dispose of in a bucket of soapy water. Reducing the number of JB decreases the attraction of other adults to the plants. Adults can also be treated with any of several insecticides.

The link below provides much detail about JB and appropriate controls:


JB populations are growing significantly. Not only do they feed on lawns and shrubs, but also on other plants such as roses, ivy, dahlia, hollyhock, rose-of-sharon and geranium. They favor trees such as Ash, Linden, Japanese and Norway maples, and Plum/Apricot/Cherry/Peach. They will also help themselves to some of our vegetable garden plants like grape, corn, beans, asparagus and raspberries.

Unfortunately, JB will continue to be a problem. Homeowners may need to begin deterring them in landscapes by reducing the plants that are attractive to this destructive insect.

More information at these links: