Cool and wet weather conditions in spring can offer a favorable environment for some common turfgrass diseases. The combination of prolonged periods of leaf wetness, weak, nutrient-deficient plants and saturated soils are ideal conditions for many of these pathogens to cause significant damage. The spring of 2011 in Ohio was so wet, in fact, that we had never seen red thread so rampant. Spring is also the time when warm-season grasses come out of dormancy and diseases like bermudagrass spring dead spot become apparent.
The emphasis for preventing and controlling these diseases should be on selecting the most genetically resistant turfgrass, creating healthy soils and performing sound turf management practices. In some instances, using a chemical fungicide may be the best option. Although we have not listed fungicides here, information is available on a regional basis from turfgrass research extension programs, such as Ohio State’s pathology website: http://turfdisease.osu.edu.
PHOTOS COURTESY OF PAM SHERRATT.
Spring dead spot (SDS) on bermudagrass first appears as circular patches of grass that do not come out of winter dormancy. These patches then collapse and leave sunken areas of dead turf that adversely affect the safety and playability of fields. SDS is a disease (pathogens Ophiosphaerella korrae and O. herpotricha) that attacks the roots and rhizomes of bermudagrass turf, therefore any remediation work done in early spring needs to be carefully administered so as not to further stress the turf. Practices such as aggressive verticutting should be avoided in order to give the turf time to recover its root system. Another problem that may occur with bermudagrass during early green-up (first new leaf initiation) is root dieback. This phenomenon, first discovered by Texas A&M in the late ’70s, describes a process whereby the root system will die rapidly, sometimes over a period of 24 hours. Loss of the root system through dieback or SDS adversely affects the turf’s ability to establish in the spring and makes that turf prone to biotic and abiotic stresses. An IPM approach to managing SDS includes:
- Choose bermudagrass cultivars with improved resistance to SDS. Since winter-hardiness of bermudagrass is directly related to its susceptibility to SDS, it’s not surprising that the most cold-tolerant cultivars of bermudagrass are better at resisting damage from SDS. A list of cold-tolerant cultivars can be found at the National Turfgrass Evaluation Program (www.ntep.org).
- Maximize soil health by alleviating soil compaction, improving soil drainage, controlling thatch, and maintaining a soil pH under 7.0 (ideally 5.5-6.0).
- Provide the turf with light applications of nitrogen in the fall (no more than .5 pound per 1,000 square feet after mid-September) and two fall applications of potassium, which has been shown to reduce SDS damage. Recovery from SDS the following spring should be encouraged by light, frequent irrigation and soil cultivation, not by heavy applications of nitrogen, since that will encourage top growth and not root recovery.
Controlling SDS with preventative fungicides requires patience as it may take several years. It is also critical to have a clear understanding of fungicide type, timing and application method. Regional fungicide trials are conducted at land grant universities/research stations and results posted on their extension websites (www.extension.org).
Snow mold is a common disease problem in northern states during early spring green-up. Microdochium patch/pink snow mold (pathogen Microdochium nivale) is probably the most common snow mold that develops during a snow event. In the absence of snow the disease is referred to as fusarium patch. Typhula blight/gray snow mold (pathogen Typhula incarnata) is the second most common snow mold. In the case of Typhula blight prolonged snow cover is required for disease development. Perennial ryegrass is particularly susceptible to snow mold, especially on immature, lush, succulent stands of grass seeded the previous fall. Prolonged rainy periods and cool to moderate temperatures in early spring are ideal conditions to prolong the disease, so it may linger until warm, dry weather arrives. A snow mold recovery plan for 2012 should include:
- Choose turfgrass varieties showing greater genetic resistance to snow mold infection (www.ntep.org).
- Check damaged areas by looking at the crowns to see if they are alive and producing new leaves. Lightly rake the grass to promote air circulation and light to penetrate the canopy and encourage new shoot and leaf development.
- If there is any dead and/or matted leaf tissue, rake and remove it immediately. In the case of dead turfgrass, renovation of the site would be recommended as soon as possible. Removing diseased and dead material in the spring is an essential part of reducing the source of inoculum on the field.
Fungicide applications at this time will not eliminate the disease from affected areas, but will protect noninfected grass, so on high-profile turf an application of fungicide may be warranted. Regional fungicide trials are conducted at land grant universities/research stations and results posted on their extension websites.
Red thread is a foliar disease (pathogen Laetisaria fuciformis) that occurs during mild temperatures and long periods of wet turf. Weather patterns in spring are conducive for the disease to become widespread, but it can occur in any season. Susceptible grasses include perennial ryegrass, fine fescue and some cultivars of Kentucky bluegrass, but all cool-season grasses have been noted to have the disease including tall fescue and creeping bentgrass. Red thread symptoms create an undesirable appearance, but crowns and roots are not infected, so plants are not killed and the turf will eventually recover. Malnourished turf often has a chronic case of red thread. Deficient nitrogen and/or phosphorous fertility levels can result in serious outbreaks. Red thread management includes:
- Choosing varieties showing greater genetic resistance to red thread infection is limited, however turfgrass varieties with different levels of red thread susceptibility are listed at www.ntep.org.
- The most important control option involves implementing an adequate fertility program. A good fertility program implemented over two to three years will drastically reduce further red thread problems. If soil is low or deficient in phosphorous, the disease is often severe.
Other cultural practices that promote healthy turf and vigorous growth also help suppress red thread. Outbreaks may be reduced further by avoiding irrigation practices that extend dew periods, like watering in the late afternoon and early evening.
Melting Out and Leaf Spot (pathogens Bipolaris sorokiniana and Drechslera poae) are troublesome diseases on perennial ryegrass, Kentucky bluegrass (especially common bluegrasses), fescues and other sports field grasses. Some leaf spot can be found on most fields in the spring, but it normally does not cause significant damage. During prolonged cool, wet weather conditions, leaf spot can progress down the stem tissue and into the base of the plants. With warm, dry weather, extensive thinning and “melting out” of turf may occur. Leaf spot is caused by several different fungi. The fungus overwinters in the thatch layer or in small lesions on leaf blades. In spring, the fungus infects young succulent leaf tissue and causes the development of small, elliptical, dark colored spots. The spots eventually turn light tan but remain bordered by a dark brown outer edge. The leaf spot phase of the disease usually does not damage the plant significantly. However, during continuous cool, wet conditions, the fungus invades the leaf sheath and crown. The fungus may also invade the crown, rhizomes and roots. As daytime temperatures increase, leaves on crown-infected plants begin to turn light green or yellow, similar to nitrogen-deficient turf. Eventually, these plants die and turn brown or straw colored. This is referred to as the melting out phase of the disease. Severe melting out can result in irregular patches of dead turf. Damaged turf often appears “thin” or uneven and tends to have weed problems. Excess thatch, heavy spring nitrogen fertilizing, excess shade, mowing too close and excessive herbicide applications can promote leaf spot and melting out. Maintenance procedures to help manage leaf spot and melting out:
- Plant more resistant cultivars of Kentucky bluegrass (www.ntep.org).
- Avoid scalping the turf or mowing too short, especially in wet, shaded areas.
- Avoid excessive nitrogen fertilization in spring, which promotes lush growth. Once in the melting out phase maintain the turf with a complete fertilizer at a modest rate to encourage healthy turf and recovery.
Manage thatch by frequent and heavy core cultivation (aeration) of the turf. This will also promote a deep, healthy root system. Also, avoid irrigation late afternoon and evening in the summer to restrict the spread of the disease.
Fungicides can be applied, but for best results applications need to be made early in the disease cycle or as a preventative treatment. This is done based on a history of the disease in the turf.
Pam Sherratt is a sports turf specialist at Ohio State University and serves on the STMA board of directors. Dr. John Street is an associate professor and turfgrass specialist at Ohio State University.