Anthracnose

• Anthracnose is a disease that causes red-brown spots on grass blades. This fungal disease can easily spread from a few inches to 10 feet of lawn, causing large brown circles. Anthracnose thrives during periods of excessive rain, and in grass with poor soil or drainage. Temperatures between 80 and 90 degrees Fahrenheit allow the disease to thrive. Underfertilization is also a contributing factor. In this case, the older blades of grass will be attacked first. You can use a fungicide to treat anthracnose, but creating a proper environment and supplementing the grass with phosphorous and potassium fertilizers can also help prevent the disease.
  
  

Leaf Spot

• Leaf spot appears as brown spots on blades of grass. These purple-brown spots will be a lighter brown-tan color in the center of the spot. Leaf spot will kill the ends of the grass, and the sheaths may also die, causing thin grass. Although this does not usually cause major problems, it can spread and cause patchwork brown spots throughout the lawn or destroy an entire lawn. Sulfur fungicide applied every three to five days can eliminate leaf spot.
  
  

Dollar Spot

• Dollar spot affects the lawn by creating a round, tan spot approximately the size of a silver dollar. Dry lawns that are not fertilized properly are choice locations for dollar spot to thrive. In the morning, the lawn will look like it has cobwebs on it, and eventually the tan patches grow together, destroying the entire lawn. Flowable sulfur fungicide should be applied to the spots every three to five days until the spots are gone, and a fertilizer with nitrogen should be applied regularly. Damaged grass can be removed by mowing.
  
  

Pests

• Brown spots on the grass blades are typically from insects eating the grass. Chinch bugs, army worms and sod webworms are pests that can create brown spots on grass. Chinch bugs cause grass to become brown and lifeless, and the damage is often confused with symptoms of drought. Army worms stay along the outside of the lawn, eating the grass down to the dirt. Sod webworms create irregular patches of brown, dead grass from the late spring through the fall. Herbicides and turf builders with insect control can eliminate the pests. Very damaged lawns may have to be replanted.
  
  

Prevention

• Seeding damaged areas of the lawn will disguise the damage done by insects and fungus after they have been treated and eliminated. Do not fertilize too frequently or with too much fertilizer, because excess fertilizer makes more grass grow, and new grass is a delicacy for fungus. Do not mow the grass when it is wet, and leave the lawn a bit longer in the summer, about 3 inches tall. Adjust the watering schedule to soak the lawn once or twice per week instead of sprinkling daily or several times per day. Broad-spectrum fungicides can be used to treat many of the diseases that affect lawns from fungus; however, these fungicides can also kill good bacteria and insects.