of Rhode Island GreenShare Factsheets
Diseases: Pythium Blights
Damping-off and seedling diseases: Pythium
fungi commonly cause seed rots and seedling death, resulting
in the poor establishment of newly seeded lawns. Infected seeds
fail to germinate. Infected seedlings are discolored, and many
topple over at the soil line and die.
Pythium blight: This
disease begins in mature lawns as small slimy or greasy looking
spots may assume a reddish color if weather conditions become
cooler and drier. When the turfgrass is wet or where air circulation
is poor, the cottony, white, weblike mycelium of the fungus
maybe observed. This disease can develop rapidly and extensively
in poorly drained areas and is especially prone to following
surface drainage channels. Other common names for this disease
are "greasy spot" or "cottony blight," and it occurs most commonly
in perennial ryegrass lawns.
Seed and seedling problems can occur at
almost any temperature but are most common at temperature extremes,
either high or low, when seed germination is inhibited. Pythium
blight is a disease of hot, humid weather when night temperatures
remain high, especially when accompanied by rain or excessive
Pythium fungi are "water molds" which
produce microscopic swimming spores. These spores are attracted
living plants. Plants that are succulent from recent nitrogen
fertilization are more susceptible to infection. The fungi
grow well in soil and thatch in wet weather and survive as
thick-walled resting spores during adverse conditions. Pythium
species are present in every soil and will grow rapidly under
Water is the most important factor in the
development and severity of Pythium diseases. To avoid seed
rots and seedling losses, care in preparation of a well-drained
seed bed is extremely important. Newly seeded lawns may require
frequent watering to hasten germination, but it is crucial
to avoid overwatering and puddling in low spots.
In established lawns. water deeply, to a
depth of 6 inches, only when necessary. Water early in the
day so leaf blades will dry. Avoid watering in the late afternoon
and early evening; do not water at night during hot, humid
weather. Prune landscape plants to encourage air circulation.
Avoid excessive nitrogen fertilizer, especially when hot, humid
weather is expected. When Pythium mycelium is active, it is
easily spread by feet and mowing. Mow turfgrass when dry to
avoid spreading the fungus. Mow low or poorly drained areas
Turfgrass seed may be treated with a fungicide
before planting, but this is not usually necessary with proper
seedbed preparation, good weather conditions, and proper seeding
Pythium blight is not a common lawn disease
in New England. Therefore, correction of drainage problems
and attention to the other cultural practices described above
are usually more effective and appropriate than fungicides.
When necessary, several effective fungicides specific for Pythium
diseases are available.
Adapted from the UMass
Cooperative Extension, 2000.
Photos from the University of Wisconsin-Madison Turfgrass Diagnostic Disease
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
of Rhode Island Cooperative Extension provides equal program