Texas Cooperative Extension
Text and images copyright © Richard Duble.
Seedling diseases create problems for those tying to establish grass
from seed in the fall. Pythium, Rhizoctonia, Helmintho-sporium,
Curvularia and Fusarium all contribute to a disease complex
causing damping-off, fading out or seedling blight. The disease attacks
seemingly healthy vigorous stands of seedlings and kills the young plants
in patches. Seedling diseases are especially damaging during adverse weather
conditions-unusually warm periods in the fall, continued wet conditions,
or cool, wet periods in early fall. Planting too early (or too late) also
increases the incidence of seedling diseases.
The terms "damping-off" or "seedling blight" are used to describe several seedling diseases. The diseases may be incited by fungi or by environmental conditions. Excessive or inadequate soil moisture, cool soil temperatures, humid and unseasonably warm temperatures, saline soils, compacted soils, or other environmental stresses can lead to damping-off or seedling blight.
Symptoms. Damping-off and seedling blight can occur before seedling emergence (preemergence) or after seedling emergence (post-emergence). Pythium incited damping-off is characterized by a high order of preemergence killing of seedlings. In this case, the deterioration process begins soon after the seed coat is broken.
In the case of postemergence damping-off, seedlings emerge above the soil and begin deteriorating at the soil level. As the deterioration progresses upward the seedlings appear watersoaked. As the tissue collapses, the seedlings shrivel and turn brown. Pythium, Fusarium, Rhizoctonia, Helminthospor-ium and Curvularia may all cause postemergence damping-off.
The effect of these seedling diseases is a significantly reduced stand of grass that usually requires replanting. If the disease outbreak is treated in time, the stand may only be thinned by the attack.
Control. To reduce the incidence of seedling diseases, plant only top quality seed. Seed that germinate quickly and produce vigorous plants are more likely to survive the seedling stage. Also, plant the seed at the proper date. Planting too early greatly increases the risk of seedling diseases. Depending on your location, cool season grasses should be planted from mid-September through November. Ideal temperatures for planting cool season grasses occur when nighttime temperatures are in the mid-60's and daytime temperatures in the mid-80's. Make an application of a soluble nitrogen fertilizer several days prior to planting to insure the availability of nitrogen. And most important, do not overwater the seedbed.
Preemergence damping-off caused by Pythium can be reduced by using seed treated with a fungicide such as Apron or Koban. Also, treating the seedbed with a broad spectrum fungicide prior to seeding can reduce the incidence of preemergence seedling losses.
After seedling emergence, fungicide applications can effectively control damping-off, fading out or seedling blight. Alternate fungicide applications between a broad spectrum fungicide and a Pythium specific fungicide at 7 to 10 day intervals during the seedling stage.
During the seedling stage, keep soil moisture sufficient to avoid drought stress. Avoid heavy applications of soluble nitrogen and mow with a sharp mower to avoid pulling up the young seedlings. Early morning syringing to wash dew off foliage will also reduce the incidence of seedling diseases.