Ascochyta Leaf Blight- Lawn disease

The Ascochyta fungi attack grasses during much of the growing season and is notorious for affecting Kentucky bluegrass when humidity and atmospheric moisture are high or when irrigations and mowing are frequent. The Ascochyta fungi seldom cause extensive damage.
This lawn disease usually does not usually kill the grass, but some turf thinning may occur under severe outbreaks
Fungicide are ineffective in controlling this disease and NOT recommended
Moderating temperatures usually bring control of the disease
Lawn maintenance with frequent irrigation are prone to this disease when temperatures exceed 90-100F for consecutive days and no rainfall occurs
Recovery may take several weeks to a month for a severe outbreak, even with cooler temperatures, rain and sufficient irrigation
Here in Colorado Springs the disease rarely occurs in the fall and affected turf generally recovers completely during the fall months

Necrotic Ring Spot

Necrotic ringspot is a lawn disease particularly damaging to Kentucky bluegrass because it is a perennial problem and the fungus attacks and kills the roots and crowns. Recovery from a disease outbreak is often very slow.
Correct excess soil acidity by liming annually to maintain a pH above 6.2. Do not apply even small amounts of fertilizer during the June-August stress period, this will tend to stimulate the disease. Fertilize only in autumn (September through November) and in late spring
Deep watering is essential for proper root growth. Water the soil in disease-prone areas to a depth of 4″ – 5″ every 7-10 days during dry periods in the summer. The harmful effects of excessive temperature can be reduced by a light sprinkling of the surface at mid-day.
Lawn maintenance is important here, cut lawns at 2.5″ – 3.5″ height, and do so often enough that less than 1/3 of the leaf blade is removed during each mowing.
Thatch (the layer of organic matter between the mineral soil and the green grass) should be no more than 0.5″ thick.
Kentucky bluegrass cultivars such as Adelphi, America, Aspen, Columbia, Eclipse, Glade, Midnight, Nassau, Parade, Touchdown, Vantage, and Windsor are less susceptible to Necrotic Ring Spot than others. Blend seed of a resistant cultivar with that of one or more otherwise desirable cultivars. Blending 10-15% (by weight) of perennial ryegrass seed into bluegrass seed will prevent this disease from occurring. Ryegrass can also be seeded into existing lawns.

Fairy Ring

Sometimes mushrooms will develop and form large circular patches in lawns. Each year the circles are likely to expand. When these circles or “Fairy Rings” are small there may be no effect on the grass, but as they continue expanding, a zone forms where the mushrooms come up. Inside this is an area of poor grass growth, or even dead grass.
Most of the Fairy Ring growth (a fungal mat) is in the ground underneath the Fairy Rings. As the ring expands the fungal growth begins forming a dense mat of dead material that creates a water-resistant layer. Penetrating this layer will help moisture reach the turfgrass roots.
Aerating the lawn several times during the growing season is also possible. When aerating over the infected area, repeat the aeration process several times.
For those who decide to live with this lawn disease, there are several ways to minimize damage to the grass in Fairy Rings. The grass should be fertilized with nitrogen several times a year to help mask symptoms. Nitrogen should be applied during the growing season.
Whichever method is used, applying a wetting agent to the area may also increase soil permeability and help to lessen symptoms.

Leaf spot

Leaf spot occurs in warm weather and is easily recognized. Spots on the leaves develop purplish-red to purplish-brown borders and brown to tan centers.
These patches may range in size from several inches up to many feet and may produce an irregular patchwork across an entire lawn.
It is particularly important to avoid excess use of nitrogen fertilizer and evening watering. Remove excess thatch — the layer of plant material tightly interwoven with living tissue between the soil surface and the green vegetation.
Fungicides may be needed to control this lawn disease. Their effect is temporary and beneficial only when combined with a change in cultural practices.

Dollar Spot

Dollar spot is one of the most destructive lawn diseases, it can develop anytime from late spring to late fall.
These patches are straw colored. Early in the morning, when the grass is covered with dew, a faint cob-webby growth may be seen on the leaves of affected plants. In the early stages of disease, leaves develop distinct tan-colored spots and bands; quite often a reddish-brown border can be seen on the leaf spots.
Dollar Spot develops at temperatures of 60 – 85 degrees Fahrenheit with high humidity and low soil moisture. The disease usually develops on lawns which are unfertilized but occasionally occurs on high maintenance lawns under stress.
Proper lawn maintenance such as fertilization and irrigation as well as adding compost are important in preventing the development of dollar spot. Fungicides may be necessary to provide control if the disease develops.

Melting Out Disease

This fungal disease affects all parts of the plant, including leaves, shoots, and roots.
Multiple dead plants form a patch and several patches will combine as the disease spreads causing the turfgrass to appear to be melting-outwards.
These fungi attack living tissue under specific environmental conditions, typically in the spring. When the fungi spores are exposed to appropriate temperatures and moisture on leaf blades for a few hours, they germinate and penetrate the leaf tissue.
Cultural Controls include improving soil aeration and water drainage along followed by re-seeding with resistant grasses. Avoid using an excess of nitrogen in the spring. If watering is required, water early in the day.