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Here: Management Updates
2004 Archive
April 29, 2004
Date: April 29, 2004
Category: Diseases
Subject: Spring Diseases, Phosphonate Fungicide Resistance
This is a difficult time of year to diagnose diseases in the field because
the environmental conditions are so variable.We can have fairly warm weather,
but still see cool weather diseases if soil temperatures are still low.
Most of the fungi that cause turf diseases can be a problem at a fairly
wide temperature range when there is sufficient moisture. Rainy weather
means more disease.
Diseases that are active now include:
- Dollar spot - if soil and air temperatures
are high enough. This is usually a sign that the turf is under
too much stress- low N, excess thatch, compaction. Fungicide
applications might not last very long if the turf is growing
quickly.
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- Fusarium patch (pink snow mold) - if soil
and air temperatures are low enough. This disease is worse
at high N and in shady, poorly drained areas. Fusarium patch
can continue into June in New England if weather remains cool.
It is easily streaked by mowers leaving greasy, reddish smears
of affected turf.
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- Yellow patch (cool season brown patch)
- if soil and air temperatures are low enough. This disease
often occurs under the same conditions as Fusarium patch.
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- Pythium root rot can occur any time but
is most likely in poorly drained areas. If conditions are
very wet, fosetyl-Al is one fungicide that can move downward
from a foliar spray.
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- Anthracnose may become active in areas
where it has been a problem in the past. The key to this disease
is to correct the stress factors that favor it. Also, avoid
dragging in sand topdressing until disease has been checked
because the fungus will enter at the abrasion wounds. In general,
take care in dragging in sand topdressing when leaf blades
are still tender and not growing quickly. This can cause a
distinctive reddish brown tip injury in bentgrass.
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Golf course superintendents may have noticed several new phosphonate
fungicides (Alude™, Magellan™, ReSyst™, Vita™)
that produce the same active ingredient in plants as fosetyl-Al (Signature™).
There are now reports of fosetyl-Al resistance with downy mildew in lettuce
in California. The downy mildew pathogen is closely related to Pythium.
The scientists warn that the repeated use of fosetyl-Al and other phosphonate
products may have contributed to the resistance problems in CA. Although
there are no reports of fungicide resistance in Pythium found
in turf, you might want to reconsider repeated, routine use of these products
in light of this new research.
- Submitted by: Dr. Gail Schumann
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