There are between 85,000 and 100,000 species of fungi of which most are beneficial to us, with only a few causing problems to the turf. By enlarge grasses are most susceptible to disease when they are stressed. Good disease control starts with sound cultural practices. Fungicides are used only as a last resort when the disease overwhelms intelligent turf management. Diseases are frequently the manifestations of other problems, and solving those problems will keep the turf healthy and avoid disease. The following practices will help to prevent disease by reducing stress to the grass. 

1. Water deeply in the morning. On established turf it is wiser to soak the grass heavily (one inch or more) but infrequently instead of smaller, frequent watering. If the grass is watered during the morning, the turf has a chance to dry out before sundown and so does not remain constantly wet.
2. Do not fertilize when it is hot and the soil is dry.
3. Do not use herbicide when it is hot and the soil is dry.
4. Limit fertilizing in the shade.
5. Use herbicides in the shade with great care.
6. Use a balanced fertilizer (see Fertilizer)
7. Avoid mowing when the grass is wet.
8. Try to reduce thatch, poor drainage, and compaction.
9. Use sharp mower blades and mow at the recommended height for you particular grass.

Common turfgrass diseases:

• Anthracnose on turf grass appears as a leaf disease, and under favorable conditions it also effects grass crowns and roots.
• Brown patch commonly starts as a small spot and can quickly spread outwards in a circular pattern up to a couple of feet wide. Sometimes the inside of the circle will recover making it look like a smoke-ring.
• Dollar spots tend to thrive during drought conditions in lawns that are lacking nitrogen. They are small silver dollar-like shape and usually look brown in appearance. 
• Fairy rings are distinguishable by circular rings filled with fast-growing, dark-green grass. Around the perimeter of the ring, the grass will typically turn brown and often times grow mushrooms. 
• Helminthosporium symptoms are manifested by leaf lesions which vary on different turf grass. As the disease advances the lesions coalesce and girdle the leaves which then die.
• Necrotic Ring Spot produces what is called frog eyed pattern. Infected leaves turn reddish purple.
• Powdery Mildew gives the appearance the turf has been sprinkled with flour. Shady areas are the most susceptible, where air circulation is poor and humidity is high.
• Pythium Blight are irregularly shaded patches of wilted brown grass with a Cobweb-like mass of fungus. Patches may form a foot or more wide. It can be a problem in dense new seeding that are being heavily watered. 
• Red Thread is ragged, blighted patches a few inches to several feet in diameter, late spring or fall, particularly on nitrogen deficient turf.
• Rust is a yellow to red, round or linear pustule that appears on leaves and stems. The disease is most severe when water, fertility, and soil compaction are less than adequate for good growth.
• Snowmolds are most common where snow falls and sits on the lawn for extended periods of time. It appears as pink to gray discolored patches of turf along the edges of melting snow.
• Summer Patch is seen as grayish-green patch of wilted grass that change to a dull blue-gray or reddish brown  then to a light straw color. Small wilted patches of grass one to twelve inches in diameter followed in subsequent years by frog eyed patches.