CONTROLLING GRUBS IN YOUR LAWN

Your turfgrass lawn can sometimes show areas of discoloration or dead grass due to a number of possible causes — drought, diseases or insects. One group of insects that draws a lot of attention is lawn grubs. These are larvae of several insect species that live in the soil and feed on grass roots. Some are natural residents of our soil and in small numbers do little harm. But if their numbers increase they may cause larger areas of damage. Warmer-than-average winter seasons can also cause greater populations.

There are invasive insects such as Japanese beetle, European chafer, Southern masked chafer and European cranefly which periodically feast on Northwest lawns. The larvae of the beetle and chafers are about 1 inch long, off-white with brown heads and curled up in a C-shape. Cranefly larvae are also about 1 inch long, gray-brown, leathery and worm-like. Adults lay eggs in the summer months, the larvae feed primarily in late summer to fall and again in spring. So any treatments should be timed for when the grubs are most actively feeding.

Some signs that a lawn is affected by grubs include sections of lawn torn up by crows, raccoons or other animals. If you try to set the damaged sections back in place, large clumps of grass may come off in your hands — evidence that the roots have been chewed away by grubs. You might see numerous white or brown grubs in the soil beneath the root zone. These are what the birds and animals are after, which can be annoying, but they actually help to reduce the grub population.

Grubs also can gain a foothold in lawns that are less healthy due to neglect or other stresses. They tend to spread in lawns which are drought-stressed, over-watered, or over-fertilized.

So the first line of defense is to keep your lawn as healthy as possible with proper watering (especially during dry summers), fertilizing, soil pH, overseeding and thatching as needed. It’s the same strategy for keeping most plants healthy and resistant from pests and pathogens, as with our own health. See our Lawn Care Calendar care sheet for more on how to keep your lawn healthy throughout the year.

If you suspect grub damage, gently cut and pull up about one square foot of sod. If you see more than about 10 or more white grubs, or 25 or more brown leathery larvae in a square foot of soil in the root zone, that’s enough to take action. First, follow the steps for healthy lawn care.

If more aggressive treatment for a large grub population is needed, we recommend beneficial nematodes, carefully following directions and most effective timing. For stronger remedies, consider using insecticide granules. Always use insecticides with care to minimize harm to beneficial insects and organisms!

For getting your lawn back in shape after any damage from grubs, birds and animals, see our Lawn Renovation care sheet.

For any additional questions, please consult one of our nursery professionals.

Swansons Nursery 9701 15th Ave NW Seattle, WA 98117 (206) 782-2543 www.SwansonsNursery.com