July 1, 2016
Brown Spots in Lawns
The warm humid conditions we’re experiencing can promote diseases such as dollar spot and brown patch. If brown areas appear in your lawn, diagnose the problem before applying a pesticide. Disease and insect pests can build up resistance to pesticides, especially if they are overused. Pesticides are also chemicals we should not put into the environment unless they are needed.
A pesticide should only be applied after a problem is diagnosed and it is determined control is needed to reduce turf injury and if it is the right time of the season to apply a pesticide for effective control.
Brown areas in lawns can be caused by a number of things ranging from diseases and insects to heat or drought stress to dog urine or gas spills. To help with diagnosis, look closely at green grass blades near the brown patches. Do this before mowing your lawn, not immediately after.
If green blades appear bleached white at the tip, this most likely is Aschochyta tip blight and lawns easily recover without a fungicide. Tip blight most often develops when hot weather follows rainy periods. After a week or two, the lawn usually grows out of the damage.
If there are tan bands with red margins all the way across the green grass blades, this is dollar spot disease. It's often brought on by low nitrogen so we recommend fertilizing instead of applying a fungicide for control. However, we would not recommend fertilizing during July and August, but you would want to be sure to make a fertilizer application in early September.
If green grass blades have irregular tan spots with red margins, and these lesions do not encircle the blade, this is brown patch disease. Fungicide applications are recommended and can be effective in stopping the spread of brown patch if applied as soon as the disease appears.
If no bleached tips or lesions (spots) can be found on green grass blades near a brownish lawn patch, then the problem might be a root disease, insect damage, environmental, or something else.
Two root diseases are summer patch and necrotic ring spot. Both are nearly identical in appearance and form the symptom known as frog-eye. The frog-eye symptom is a brown to tan patch of grass with a tuft of green grass in its center.
The two fungi that cause these diseases infect roots in the spring; even though symptoms do not begin to appear until late spring for necrotic ring spot or mid- to late summer for summer patch after the disease weakens the root system.
Fungicides can help reduce these two diseases, but are best applied in mid-April and again one month later for Necrotic ring spot; and in early to mid-May and one month later for summer patch. For both diseases, overseeding with disease resistant cultivars will provide the best control in the long run.
As for insect problems of lawns, our most common insect pest is white grubs. It's too early for white grub damage. However, now is the right time to apply insecticides containing imidacloprid to lawns with a history of grub damage. Other grub insecticides should be applied around the first of August. With any of these treatments for grubs, they need to be watered into the soil with a single application of at least a half inch of irrigation if we don’t get that much in the form of precipitation.
Keep in mind repeated applications of insecticides containing the same active ingredient year after year could result in grubs building up a resistance to these chemicals. It is best to apply these products only to lawns that have had a recent history of white grub damage. If you need to treat again next year, use an insecticide with a different active ingredient.
For more information on lawn disease and insect control, contact your local Nebraska Extension office.