Lawns - Common Turf Diseases
What Causes a Turf Disease or Fungus???
There are many disease or fungi that attack lawns. Some diseases or fungi cause cosmetic damage, that will eventually clear up with out damage to your turf grass. Other diseases or fungi can cause complete destruction to you turf grass. Each disease requires an environmental condition, hot and dry, hot and humid, cool and wet, or cool and dry. It is impossible to control the environment to exclude all diseases. Many diseases can be controlled by applying the proper fungicide at the correct time.
Brown Patch
Brown Patch is probably the most wide spread destructive turf disease in the United States. It can cause severe damage overnight when temperature and humidity are very high. The disease begins at a central point and spreads outward in a circular pattern and can be almost any size. Often in the early morning a “smoke-ring” or strip of gray mycelium is visible around the perimeter of the diseased area. Applying a fungicide is a must in the very early stages of the disease.
Symptoms
- Irregular, circular, sunken pockets of dead, brown grass (from a few inches to several feet in diameter).
- Dark purple rings (“smoke-rings”) may form around infected area in hot humid weather.
Favorable Conditions for Development
- Warm, humid, wet conditions
- Temperature: 80-85 degrees Fahrenheit
- Warm evening temperatures
- Improper pH
Preventative Control
- Slow release fertilizers
- Increase air movement
- Water infrequent, but heavy, in the a.m.
- Remove dew
Leaf Spot
Leaf spot is one of the most common turf diseases and is especially destructive to bluegrass. Leaf spot is active in spring, early summer and fall when conditions are excessively moist. When not controlled, it often progresses to the crown or even the roots of the plant. Fungicide is used to treat serious outbreaks.
Leaf lesions occur on the leaf blade and sheath. New spots are uniformly brown to purple and are most prevalent along the margins of leaves. As spots age, they become elongated parallel to the leaf axis and enlarge up to 1 x 4 mm. The centers of older spots become tan to gray, and during warm, moist weather. Severely affected leaves may die, causing the turf to become thinned.
As with all diseases, how the turf is watered, fed and mowed makes a huge difference. It’s best to be sure the grass does not stay continuously wet or become excessively dry.
Water no more than once per week and soak the soil to a depth of 6''. Water in the morning so the grass will not remain wet for long periods. Open the area around the grass crowns (where the plant goes through the thatch and into the soil) with core aeration. And keep the lawn properly fertilized and regularly aerated. Collecting the clippings during the spring and fall (leaf spot stage) will help reduce the spread of the disease. Treatments, if needed, should begin early. Spring and early summer applications of fungicide can be effective, but little can be done to reverse the disease once the melting-out phase begins. The melting-out phase begins during hot, dry weather and causes large irregular areas to appear dried out. There may not be any distinctly visible symptoms during the melting out phase, as the damaged areas may appear very similar to the effects of dry weather or insect injury.
Dollar Spot
Dollar spot is a common and persistent disease that occurs on most turf grass species throughout the world. The dollar spot fungus survives unfavorable periods as mycelia in infected plants and as stromata on foliage surfaces. Dissemination occurs when infected leaf debris is moved by equipment, people, animals, water, or wind. When the environment favors fungus activity, mycelium from within infected tissue or from stromata colonizes nearby healthy foliage. Under humid conditions, mycelial growth may extend out of the tissue into the air. When this aerial mycelium contacts a moist leaf surface, it may penetrate the leaf and cause an infection. Prolonged high humidity within the turf grass canopy is required for fungal growth. The dollar spot fungus may commence activity from late spring through late autumn. Favorable environmental conditions for disease include warm, humid weather and cool nights that result in heavy dews. A temperature range of 60 degrees F (15 degrees C) to nearly 86 degrees F (30 degrees C) appears favorable. Even though high humidity in the canopy is required for infection, dry soil conditions increase disease severity. Similarly, low nitrogen fertility increases disease severity. Soil pH and phosphorous fertility levels have no apparent influence on disease severity.
Disease Management
- Maintain adequate to high nitrogen fertility during the period of dollar spot activity.
- Water thoroughly (deeply) but as infrequently as possible without causing drought stress.
- Time irrigation to minimize leaf wetness. Avoid late afternoon and early evening irrigation.
- Promote good air circulation over the turf by pruning or removing trees or shrubs and removing other barriers.
- Temporarily increase mowing height during disease outbreaks.
- Reduce compaction and thatch with core aeration.
Red Thread
Red thread occurs in the spring and fall during humid periods when the air temperatures are between 16°C and 24°C (60°F and 75°F). The disease is especially severe on slow-growing nitrogen-deficient turf. Bluegrasses, fescues, ryegrasses, and bent grasses can be affected. Fine-leaved fescues and some ryegrasses are particularly susceptible. The first noticeable symptoms are water-soaked patches of grass in the spring. Infected grass blades soon die and fade to a bleach-tan color when dry. When infected leaf blades are often interspersed with healthy unaffected leaf blades giving the grass a ragged appearance. In severe cases, most leaf blades may be killed and diseased grass looks scorched or yellowed in irregularly shaped or circular patches from 5 to 50 cm in diameter. The patches may be widely scattered or, if close together, may coalesce into larger spots.
In humid weather, the fungus grows visibly on the infected grass blades and leaf sheaths. The fungus produces thread-like strands or web-like areas of coral-pink to blood-red hyphae on the tips of brown grass blades. The strands can protrude up to 2 cm upward from the blade tips and are easily seen, hence the name "red thread disease".
The fungus may produce spores for dispersal, however, the primary means of dispersal is the spread of infected tissue and bits of the "red thread" to healthy areas of grass. This type of spread depends upon mowing, foot traffic, and other activities, which occur on the diseased turf. Invasion by the fungus is quick, and leaves may begin to die two days after becoming infected. Fungal hyphae and dried pieces of the fragmented "red thread" enable the fungus to survive when conditions are not favorable for disease development (winter, mid-summer, etc.). During dry conditions, the "threads" may be viable for up to 2 years.
To Avoid or Treat Red Thread
- Maintain adequate soil fertility. The actual fertilization rates will depend upon the types of grass grown, soil texture, and the specific rates recommended in your area.
- Where red thread has been a problem in the past, maintain a soil pH of 6.5 to 7.0.
- Avoid over watering.
- Do not water the lawn in the late afternoon or evening.
- Provide good soil drainage.
- Plant trees and shrubs far enough apart so that large areas of grass do not remain shaded for long periods during the day and so that dew and other moisture on the grass will readily evaporate.
- Selective pruning of established trees and shrubs may also help.