Fungus attacks like lawn blight are the most detrimental to bluegrass. The grass develops dead rings and the roots of the dead parts are rotten. Some kinds of lawn blight also develop material on the grass that looks like spider webs. Necrotic ring spot develops in temperatures between 70 degrees and 80 degrees Fahrenheit. Fusarium develops in temperatures between 70 and 90 degrees Fahrenheit.
Lawn blight is best prevented by not overwatering. The blight can also be caused by overfertilizing the lawn. The extra nitrogen can cause the grass to grow too much, which can require more frequent mowing and increase the amount of thatch. Landscapers can create grass more resistant to lawn blight by allowing the grass to grow a little taller, which can encourage deeper root growth and cause the grass to be more resistant to the lawn blight. Another way to protect the lawn is to till the soil. Tilling the soil can increase air circulation, which is not good for the fungi causing lawn blight.
Thatch should be kept to a minimum when the lawn has become infected with blight disease. Thatch is a layer of partially decomposed grass. Thatch can be reduced by using fertilizer with a lower nitrogen content. Thatches are best removed by using a power rake on the grass. The blades should be kept sharp to prevent the grass from being wounded.
Grass normally needs to be watered very deeply and infrequently. However, grass that has developed blight should be watered more frequently, yet should only have the top layer watered to not encourage the growth of the fungi that causes blight. Watering is best done in the heat so that the water does not remain soaked in the soil overnight. Some gardeners choose to not water their yard at all after the yard has been struck with blight. This can be effective as it starves the fungus of essential moisture. Another approach is to mow the brown patches very short in September and then replant seeds so that new grass germinates.
Fungicide is available that can be used to kill the fungi that causes blight, though fungicide is not always effective. The fungicide is the most effective if it is applied in the early parts when the fungi has just developed. One kind of blight that must be killed with fungicide is fusarium. Fusarium blight looks like long streaks or crescents of dead spots.
Many gardeners think that grass clippings can spread the blight throughout the yard. However, most yards are already covered with fungus spores and these methods will do nothing to prevent the spreading of the fungus.