What’s causing the brown spots in my lawn?

Brown spots in lawns could be from the frigid late November cold snap killing Bentgrass blades and stems, to the warm wet winter weather encouraging early crane fly larvae feeding and damage and Microdocium Patch and Red Thread fungus infection.

Bent grass tops damaged in freeze

Bentgrass tops damaged in freeze

Dead Bentgrass tops
Native Bentgrass is a weed grass found in most lawns over a few years old. The November freeze damaged the tops and has been the cause for the most concern by homeowners. The damage should mow off and the grass should recover without any treatments. The close mowing, down to 1”, can be done any time now. If mowing doesn’t remove most of the dead grass, dethatching may be necessary. Call us for a referral for companies who offer that service and make sure to mow close once every spring.


Larvae and crane fly damage


Checking For Larvae
Watch for starlings and crows feeding, usually in wet and shady areas. Those would be the first place to check but any area that looks thin is suspect. Dig up some sod down to the soil, the larvae will be in the thatch layer just above the soil. Tear apart the sod and if you find several in a small area, it may be wise to consider treatments. A few here and there should not be a concern, in fact WSU sets 12-24 per square foot as the threshold number for treatment. At that number the grass may thin out enough to require reseeding.

Larvae Feeding
There are two types of crane flies in our area, the European Crane Fly and the Common Crane Fly. Their life cycles overlap creating an ever increasing problem for control. We’ve seen some lawns devastated within the last month like the one in the picture. In addition, we are finding a new lawn pest, the Large Yellow Underwing Larvae that has a history of destroying lawns in other parts of the country in as little as 48 hours! So far that pest has not been found in large numbers except for one lawn in northwest Olympia off 36th Ave, but we are finding a few here and there, so it’s just a matter of time. The picture shows all three found in one lawn in northeast Olympia recently.

The warm winter weather has been perfect for patch disease infection. All of them are transient and controllable with treatments if necessary. You’ll find pictures of the damage and information on control measures here.