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Over the Fence

Where gardeners come to find out what's happening out in the yard.

Sod Webworms and Grubs

Posted by Richard Hentschel -

Gardeners would normally see damage from grubs or sod webworms this time of year. With our rainfall this summer, grub damage if they are even out there will be minimal. The winter weather took out a large percentage of the Japanese beetle grubs, so we have not seen that big population we have in the past. Our more native Masked Chafer grub population having been displaced by the Japanese Beetles so without them, grub damage could be low in the home lawns. Grub damage occurs when the grubs are feeding on grass roots faster than the grass can replace them. It takes more than 12 grubs per square foot to show damage. The lawns have been able to grow quite well with all the rain and have not really seen a strong dormant period all summer. If the lawn has seen digging activity by raccoons or skunks, then grubs are present usually. This does not mean a treatment is automatically needed, only if the threshold exceeds 12 per square foot and the lawn is suffering.

Sod webworm damage shows up as closely clipped lawn, as the webworm feeds above the soil and thatch, clipping off and then digesting green grass blades. The webworm will spin silken tubes within the thatch layer where they rest during the day. Here again with all the rain, the grass has been actively growing, so damage may not be extensive. Mother Nature helps us control webworms through a couple different ways. Birds love webworms. In particular, starlings will show up by the dozens to feed in the lawn if webworms are present. If you see what look like cigarette filters strewn in the lawn, they have been there. Those are the silken tubes left behind by the birds. There are naturally occurring organisms in the soil that will infect the overwintering larvae too. This lessens the potential population and any subsequent damage.

Management of either the grub or webworm first depends on proper identification of the damage and then determining if there are enough of them to warrant control. Grubs feed below ground and the grass can be pulled up as if it were sod having just been layed. Webworm damage is above ground and the grass remains firmly rooted. Any treatment if needed need to be placed accordingly. Webworm treatments are not heavily watered in or at all depending on the label instructions and grub control will typically need to reach the root zone where feeding occurs. If the grub is that of a Japanese beetle, milky spore can be a treatment. Milky spore is not always consistent in controlling the grub.



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