MELTING OUT
- Pathogen: Drechslera poae.
- Grasses
Affected: Kentucky bluegrass (Poa pratensis),
annual bluegrass (Poa annua), Canada bluegrass (Poa compressa),
rough bluegrass (Poa trivialis).
- Season
of Occurrence: Spring and early summer.
- Symptoms
and Signs: The disease occurs on all
plant parts. On the leaves, it is
first seen as minute, water-soaked lesions. These soon enlarge into dark, purplish-red ovular areas ¼ to
3/8 inch long and 1/16 to 1/8 inch wide.
As the lesions enlarge, the color of the centers changes to brown,
and finally to a dull white.
Lesions on the leaf sheath are generally not as regular in outline
as those on the leaf blades, and the lighter colored center is usually
missing. Colonization of the
sheath tissue is often so extensive that the leaf is girdled at this point
and drops from the plant. It is
this leaf-dropping phase of the disease that has given rise to the name
“melting-out”. During severe
outbreaks of the disease, bluegrass stands are commonly found with less
than six leaves per square foot of turf grass area. Infection and colonization of the crowns,
roots and rhizomes occur in conjunction with the leaf leisioning phase of
melting out. The disease in these plant parts develops as a rot, appearing
at first as a reddish-brown decay and finally turning dark brown to black
as bacteria and other fungi begin to colonize the tissues.
- Conditions
Favoring Disease Development: Melting out is a cool, wet
weather disease. Optimum weather
conditions for development of its leaf lesion phase are air temperatures
in the 60-75°F range and extended periods of rainfall. Tuft cut at a height of 1 inch is more
susceptible to the disease than those mowed at 2 inches. Also as a general rule, the severity of
melting out is greater when Kentucky bluegrass turf is growing under high
nitrogen fertilization. With the
advent of warm summer months, colonization of the plants is limited to the
crown and root tissue. However, if
cool, wet weather develops during this time, lesions can recur on the
leaves.
Control (1) Cultural Practices: In
turf with a known history of melting out, the total amount of fertilizer used
annually should be divided between fall and spring applications. Applications of high rates of readily
available nitrogen fertilizers to the turf in the spring should be avoided. If spring fertilization is practiced, the
nitrogen component of the mixture should be a slow release formulation. When feasible, clippings should be
removed. Also, since cutting heights of
less than 1.5 inches will result in an increase in the severity of both the
foliar and crown rot phases of the disease.
if the use pattern of the area permits, the turf should always be mowed
at cutting heights in the 1.5 to 2 inch range.
If the management program for a stand of Kentucky bluegrass with a known
history of melting out does call for a cutting height lower than 1.5 inches,
the area in question should be monitored closely and a fungicide program
initiated immediately at the first indication of an outbreak of the
disease. (2) Call Empire Tree and
Turf for a free estimate for a fungicidal program for your turf grass.
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