Yellow Spots on Blades of Grass

Causes

• Yellow spots are caused by many diseases, pests and poor care. A disease called iron chlorosis, which indicates a nitrogen deficiency, manifests itself in the form of yellow spots in the lawn. Take-all patch, another disease, also causes the grass to turn yellow. Yellow patch causes large spots or patches with yellow margins in the lawn. Chinch bugs cause irregular brown spots on grass that turn yellow. Other reasons for yellow spots include too much fertilizer and improper watering.

Symptoms

• Symptoms of iron chlorosis include completely yellow or striped yellow and green patches of grass blades on alkaline soils with high phosphorus levels. Commonly occurring from fall through spring, symptoms of take-all patch include yellow grass blades with dark roots and thinning of turf. Grass pulls out easily if root rot is excessive. Yellow patch manifests itself as 6- to 12-inch-wide patches on grass blades that occur in excessive shade and moist conditions. Chinch bugs are tiny insects that suck essential juices from grass blades, causing patches to turn yellow then brown. Excessive fertilizer or improper fertilization timing scorches the lawn and strips it off its color. Overwatering causes grass blades to wilt and tips to turn yellow, while underwatering causes grass blades to fade to yellow before turning brown and drying.

Treatment

• To treat iron chlorosis, use a foliar application of iron sulfate, spread 1/4-inch-thick compost over the turf and aerate the lawn one to two times a year. To treat take-all patch, mow your lawn slightly higher than the recommended height to reduce stress. Also avoid over-fertilizing your grass, since excessive nitrogen causes the disease. The damage by yellow patch is mostly cosmetic and symptoms disappear after a week of warm weather. However, use a registered fungicide if the outbreak is severe. Aerate the soil one to two times a year to treat chinch bugs and apply a registered insecticide to deter the pests. To prevent fertilizer burn, feed your lawn the recommended amount of fertilizer at the specified time. Ideally, feed the lawn in fall and end spring to promote healthy roots. Provide your lawn 1/2 to 1-1/2 inches of water every week during the summer, depending on the heat.

Prevention

• Keep your grass in good health and stress-free to keep yellow spots from occurring. Refrain from using high-nitrogen fertilizers and overwatering your lawn, since these conditions encourage fungal growth. Avoid mowing your lawn grass too short.