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.