When lawns are stressed from extended periods of hot, humid conditions, conditions are right for fungal diseases and the damage they cause. Similar to weed control, the best way to deal with lawn diseases is through prevention. Promote a healthy lawn with an extensive root system and allow for adequate air and water movement.
But even the healthiest lawn can come under attack by these invaders, so let's look at several of them below.
(Need help with lawn disease pictures? Find sources in our article.)
One of the most common lawn diseases, dollar spot gets its name from its distinct pattern of dead circular patches about the size of a silver dollar. It occurs when moisture is present during the warm day/cool night patterns of spring and fall. Excessive thatch, poor drainage, overwatering and low soil fertility can all aid in bringing on dollar spot.
Most prevalent in tall fescue and ryegrass, brown patch can attack all other cool season grasses and some species of warm season grasses. Brown patch is notable for it's distinctive "smoke ring" that is sometimes visible on the outer edge and it's "frog-eye" appearance as grass in the middle recovers giving the area a ringed look. Brown patch occurs during extended periods of heat and humidity, especially when nighttime temperatures remain above 68 F. Poor air circulation, overwatering, overfertilizing and lawn compaction can also exacerbate the situation.
Often found on Kentucky bluegrass lawns located in shady areas with limited air movement, powdery mildew looks like a white dust covering the grass blades. Although it can yellow the turf over time, powdery mildew is not likely to cause widespread damage to a lawn. Extended cloudiness can bring on powdery mildew but if the problem is not weather related, conditions may need to be altered for a healthy lawn.
Shade tolerant grass species are not likely to attract powdery mildew and pruning or thinning trees can improve air circulation and sunlight to the area.
The infamous circles on the lawn. Fairy ring can be a dark circle or partial circle on the lawn than may or may not grow mushrooms. Once thought to be a portal to elf kingdoms, relatively little is still know about their origins or how to get rid of them. There are many stories about digging out fairy ring but the widespread nature of the fungal spores leads to limited success trying to dig the ring up. Maintaining a lush green lawn can blend in the darker color and regular mowing can help control the presence of mushrooms.
Prolonged snow cover in the spring can lead to gray snow mold or pink snow mold, especially if the ground is not quite frozen. It can also occur on over-fertilized lawns and under leaves left over from the fall. Snow mold damage is largely superficial and temporary, the best way to deal with it is to rake it out to help the area dry. New growth will begin and soon the damage will be gone.
A common and relatively harmless lawn disease, the red thread usually appears when the lawn is due for fertilizing.
Chances are if the red thread is present, it's time to fertilize the lawn. Red thread is noticeable by its distinctive red hairs amongst the turf giving it a pinkish/red appearance from a distance.
Although not really a lawn disease, dog spot is often mistaken for a lawn disease. Circles of dead grass are often what's left behind when dog urine is concentrated on the lawn, similar to diseases like dollar spot or brown patch. Training dogs to do their business in certain areas can help as can motion activated sprinklers. There is also an abundance of products available to either feed the dog or treat the area but buyer beware. To many, dog spot is just a fact of life.