dead grass circles in lawn

Asked September 12, 2019, 7:08 PM EDT

Two years ago we had one large area about 12 feet in diameter in our grass go dead. Our landscaper took care of it in the spring by spreading some sort of pesticide. He said it was from eggs that were deposited by these daddy long legs type of flying bug. He threw down some grass seed and it grew back very nicely. Along about the middle of this summer, we started getting some dead grass areas in a different part of our backyard. The dead grass areas are like that where our female Labrador dog would urinate, although our dog does not urinate in that part of the backyard. The circular areas are about 12-15 inches in diameter (see the attached images). During the summer we would have about 8-12 crows at a time that would come and feed in our backyard grass. We haven't seen any grubs in our garden that surrounds half of our backyard. And we haven't had any problems with insects or bugs on all of our plants. Our roses did very well this summer. However, we think that we're having some pesticide problems again with our backyard grass. What do you suggest we do? Thank you for your help. Gregg & Lee Ann Childs gechilds@comcast.net

Washington County Oregon lawns and turf

1 Response

Hello,

Given the timing, it sounds like it is bill bug larvae. The crows are the first clue. Anytime crows are landing on your lawn and pecking, they are likely foraging for insects. The other insect problem you had was European Crane fly larvae. Note, the adults do not do any damage.

Crane fly larvae feed primarily on the grass leaves first and thin your lawn. Bill bug larvae eat the roots and the grass dies of drought stress because it can't get any water. There is no point spraying for the bill bugs now as they are done feeding and won't return until next spring (Adults which lay eggs). The larvae hatch and then start eating your grass in late spring and early summer.

There are a couple of approaches you could take. The first approach I would recommend is next May and June begin scouting for them by digging a 6 inch square hole in your lawn. Turn the sod over and filter through it with your hands and see if you can find the larvae. See photo below. If you don’t find any, simply replace the sod and dig in a different place next time. If you find larvae, you can then hire a licensed pesticide applicator to apply an insecticide.

The second approach is if you want to treat preventatively, you need to apply an insecticide in April-May time period. Systemic insecticides are the longest acting since they are taken up by the grass. Many of the insecticides are harmful to bees so applying at dusk is the best time to avoid killing bees. Also, Acelepryn is the only product that is soft on bees but it may be more expensive than the other systemic insecticides. The neonic class of insecticides (examples include Arena, Meridian, Merit, Zylam) are very effective as well, but there have been some restrictions placed on them in Oregon because of bee kills. They were applied to Linden trees at the wrong time. I would hire a licensed pesticide applicator who knows the rules in Oregon surrounding the use of neonicotinoids and only apply when bees are not foraging. There are some other insecticide options that your applicator might discuss with you that can also work. I have just highlighted the ones that I know are the most effective. If you are concerned about bees, use Acelepryn.

As far as fixing your lawn, I would de-thatch the dead areas and reseed. It is the perfect time to do it right now. If the areas are small enough, you can rake them with a metal tined rake. Be sure to get good soil to seed contact.

Just a note: generally crane fly larvae do damage in the winter months. They finish feeding generally around April, but you would see damage way before then if you had high populations. You can scout for them in December and January similar to how you scout for bill bug larvae but they look totally different and you need 25 – 50 per square foot before you will see any damage (see photo below) whereas, with bill bug, the threshold is closer to 5 per square foot.

Good luck.