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Introduction
These common leafspots encountered in New York are most destructive
during cold, wet, overcast weather such as occurs during spring and
fall. They are also common where turf is sprinkled with water frequently.
Leafspots cause gradual browning and thinning or melting-out of grasses
and, if severe, the entire turf may be lost. Crown and root rotting
often follow leafspotting as the season progresses and temperatures
rise. Diseases caused by the species of Drechslera and Bipolaris
were formerly grouped together as Helminthosporium leafspot,
crown rot, and root rot. Now, however, they have been segregated out.
Many species of Drechslera cause what is known today as Drechslera
leaf spot, crown rot, and root rot.
Symptoms
Small, dark-brown, purplish, or purplish-red colored spots appear
on the leaves from the early spring to late fall. As these leafspot
lesions increase in size their centers may fade to a straw or light-brown
color. The spots are usually surrounded by narrow dark reddish-brown
to purplish-black borders. As the disease progresses in favorable
weather, the spots run together and girdle the leaf blades. The crown
rot stage appears with the first warm weather, causing a reddish-brown
decay of the crown, rhizome, and root tissues. Plants lack vigor and
wilt during mid-day as the root are destroyed.
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Figure 1: Drechslera spores |
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Disease cycle
The fungi which cause the disease survive from year to year in
dead clippings or infected grass plants. Spores are produced in
the spring and carried to new leaves by air currents, mowers,
splashing water, feet, etc. The spores germinate in a film of
moisture and infect the leaves, causing spotting. New leaf infections
may occur as long as the weather remains moist and the temperatures
are favorable. With the arrival of relatively dry weather in the
summer, the leafspot phase decreases and crowns and roots are
attacked. Crown and root infections in midsummer lead to the melting-out
phase of the disease and large patches of turf may be killed.
Management Strategies
Mow grasses at the recommended maximum height for satisfactory
turf use. Mowing should be done frequently so that no more than
1/3 of the leaf surface is removed at any one time. Avoid letting
thatch accumulate over 1/2 inch in depth. Fertilize on a regular
program to maintain as uniform a level of soil nutrients as possible.
Use a balanced fertilizer, and avoid applications before late
May or early June. Avoid excess nitrogen, especially in the spring.
In dry weather, apply enough water to soak the soil at least six
to eight inches deep. Frequently sprinkling and water-logging
the soils should be avoided. Many Kentucky bluegrass varieties
are resistant to this disease (Bonnieblue, Bristol, Challenger,
Eclipse, and Midnight) whereas most fescues are susceptible. Reliant,
a hard fescue, has excellent tolerance to leafspot diseases. Spartan,
Tournament, and Waldina (all hard fescues), and Shadow (chewing
fescue) have good tolerance to such diseases.
For homeowners, several fungicides may be used in aid in disease
management. These include fungicides containing the active ingredients captan, chlorothalonil or chitosan. Before purchasing,
be sure the product is labelled for the intended use; apply fungicides at intervals recommended
on the packaging label during cool, moist weather from April to
June. September and October applications may be necessary if favorable
weather persists. Avoid the use of "systemic fungicides"
such as benomyl, thiophanate-methyl, or triadimefon on leafspot-affected
turf. These fungicides will tend to increase the severity of disease.
Created, KLS, 8/99; Updated, SLJ, 1/07
This publication contains pesticide recommendations. Changes in pesticide
regulations occur constantly, some materials mentioned may no longer
be available, and some uses may no longer be legal. All pesticides distributed,
sold, and/or applied in New York State must be registered with the New
York State Department of Environmental Conservation (DEC). Questions
concerning the legality and/or registration status for pesticide use
in New York State should be directed to the appropriate Cornell Cooperative
Extension Specialist or your regional DEC office. READ THE
LABEL BEFORE APPLYING ANY PESTICIDE. __________________________________________________________________________________
The Plant Disease Diagnostic Clinic
at Cornell University is located at 334 Plant Science Building,
Ithaca, NY, 14853. Phone: 607-255-7850, Fax: 607-255-4471,
Email: kls13@cornell.edu
or slj2@cornell.edu
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