Grub infestation

Asked August 1, 2020, 10:53 AM EDT

Last spring I had unusual amount of birds looking for worms in the grass. I now have a lot of dead spots forming and thought extra spot watering would help, also when I use the hose nozzle on the spot it reveals occasional black like bugs that don't seem to move. My first guess was maybe grubs, if so, I have read that the product recommendation to kill is not really good for humans and it needs to be applied in early spring. I have given up at this point in summer on my lawn recovering due to the widespread damage. I also read that if it is grubs they will return year after year. If it is Grubs what product do I use and what time of year do I apply and is there a eco friendly product I can use? I am paranoid when it comes to unfriendly chemicals. Any help would be appreciated. Thank you, Henry

Clackamas County Oregon

1 Response

Grubs are growth stages of scarab beetles. We do have grubs in Oregon from a couple of beetle species, notably Japanese beetles and June beetles. If you don't see the grubs, it doesn't mean you don't have them. You can do a more thorough search for them by digging up a square of lawn and soil, sort through the sod, and sift the soil for them. This article has pictures of the grubs, descriptions of the damage you see and how to treat the lawn, White Grubs in Home Lawns https://ento.psu.edu/extension/factsheets/white-grubs-lawns. Grub damage is usually seen in the spring and in the fall.

However, there are many causes of brown spots in lawns during summer. It's important to identify the cause of these spots in your lawn so you can take appropriate action and fix the real problem. Incorrect watering, fertilizing, mowing height and frequency, poor drainage, soil compaction, and extremely high temperatures are physical causes. In our area we get very little rain if any in July and August, at the time when we have our highest temperatures. Watering long enough to get water down to the roots during this period, and at the correct frequency is crucial to lawn health. Plants draw considerable amounts of water up during hot weather in order to stay hydrated. To determine the amount and evenness of water delivery conduct the "catch can tests". Set small, empty, straight sided cans (like tuna fish cans) every 10-15 feet around your yard. Run the sprinkler system for 15 minutes and measure the amount of water in each can, average the amount for the lawn by totaling the water amounts divided by the number of cans. Compare the average with Portland's Water Consortium's (www.conserveh20.org) weekly water number to determine how long you need to water for that week. The weekly water number takes into account current temperatures, humidity and any rain.

You could also have a disease problem going on. Most are fungal. The fungi damage the grass leaves so they cannot withstand hot dry weather. Some of the fungi whose effects are most visible in hot dry weather include Fusarium blight, gray leaf spot, leaf spot, Pythium blight, and Rhizoctonia blight. This article has excellent information on the causes of dead spots in lawns with pictures of the above diseased lawns, predisposing conditions, prevention and treatment. Lawn Diseases: Prevention and Management http://ipm.ucanr.edu/PMG/PESTNOTES/pn7497.html.

This article has comprehensive information specifically for our area on lawn management, Practical Lawn Care for Western Oregon https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/ec1521.pdf.

There is a wonderful smartphone and desktop App "Grow Smart Grow Safe" that can help you navigate evaluating and selecting the various herbicides, pesticides, and insecticides available on the market by their active ingredients and relative safety using a color-coded rating process for relative toxicity.