Turfgrass Diseases: Damping-Off Diseases (Causal Fungi: Pythium, Rhizoctonia, and Fusarium spp.)
Turfgrasses in the seedling stage are particularly susceptible to the disease-causing activities of certain soil-borne fungi, including species of Pythium, Rhizoctonia, and Fusarium. Damping-off diseases are most likely to occur during hot, humid weather in summer, but can sometimes take place in spring and fall during periods of wet weather. Seedlings affected by damping-off diseases rarely recover and damaged areas often have to be reseeded.
Symptoms and Signs
Seedlings become blighted, then collapse and die, forming circular or irregular patches. Affected areas sometimes appear as streaks on sloped land or in drainage swales. Diseased plants are often water-soaked and slimy. Sometimes, white, fluffy mycelium can be observed on dew-covered grass in the morning. Dead tissue often mats together and forms a diffuse crust over the soil surface.
Disease Cycle
Most soils contain fungi that can cause diseases of seedlings. When conditions are favorable for turfgrass seed germination and growth, as in early fall and spring, these soil-borne fungi are relatively inactive and usually are of little concern. During warm, wet weather, however, the soil environment is more favorable for disease-causing activities of these fungi and less favorable for seedlings and severe damage to new turf stands can result.
Disease Development
Damping-off disease outbreaks tend to be associated with high temperatures and humidity, water-logged soils, high rates of fertilizer and mulch, as well as excessive seeding rates. In warm weather, higher-than-normal rates of seed may produce a very dense stand of seedlings that will create a humid environment near the soil surface. Such conditions are ideal for disease-causing activities of Pythium, Rhizoctonia, and Fusarium fungi. High rates of fertilizer can produce a succulent turf that is more susceptible to infection by damping-off fungi, especially when seeding takes place in early to mid-summer.
Cultural Control
Cultural control of damping-off diseases is based on providing favorable conditions for germination of grass seed and growth of turfgrass plants while minimizing conditions that favor the fungi. Often, this can be accomplished by planting in spring or late summer (late August or early September in Pennsylvania) when night and morning temperatures are cool. For summer seedings, do not apply excessive amounts of seed and fertilizer, and prevent free water from standing on the soil surface. It is also important to avoid using excessive quantities of mulch following seeding.
Chemical Control
Control of damping-off diseases can be achieved with preventative fungicide applications or applications of fungicides after symptoms appear if the disease is detected before significant damage occurs. One of the difficulties in chemical control is determining which fungus is inciting the disease, as some fungicides control only one type of fungus and have no effect on others. If unsure of which pathogen is causing a damping-off disease, try to use a fungicide or combination of fungicides that control fungi in all three genera. Unfortunately, few fungicides are labeled specifically for Rhizoctonia and Fusarium damping-off diseases.
Fungicides labeled for Pythium damping off include Terrazole (etridiazole), Subdue MAXX (mefenoxam), Banol (propamocarb), Segway (cyazofamid), Disarm and Fame (fluoxystrobin), Disarm C and Fame+C (fluoxystrobin + chlorothalonil), and Disarm M (fluoxystrobin + myclobutanil). Although not labeled specifically for Rhizoctonia damping off, Disarm and Fame fungicides control other diseases caused by Rhizoctonia.
