Home Lawn: Turf Tips
Managing summer
lawn diseases
We encounter most turf diseases in home lawns during the
spring when temperatures are moderating and afternoon spring showers
are plentiful. However, our summer days can also present several turf
disease problems, especially when we encounter several consecutive days
of cloudy, wet weather.
Gray Leaf Spot (Piricularia grisea)
of St. Augustinegrass can cause severe thinning of home lawns during
the heat of summer. This disease is more common during extended periods
of hot, humid weather. Although primarily a disease of St. Augustinegrass,
it is also found on crabgrass and occasionally on centipedegrass. Infected
turf will have irregular gray, dirty-yellow or ash-colored spots with
brown, purple, or water-soaked borders on leaf blades. The disease
is usually noticed first in shaded areas that remain damp longer. Under
heavy disease development, the grass may have a burned or scorched
appearance resulting in death or severe spotting of the leaf blades.
Fungus spores are carried to sites of new infection by the wind, splashed
rain, irrigation water, and mowers. Seldom will this disease kill an
entire lawn but can thin it severely enough to be unsightly and encourage
weed infestations.
‘Helminthosporium’ Leaf
Blights (Bipolaris spp., Curvularia spp., etc.) are probably
the most serious summer diseases of bermuda grass and zoysia grass
if left unmanaged. Symptoms are round or oblong spots on the leaf
blades and are usually brown or purple in color. As the disease infections
increase the leaf sheaths turn brown and die. The turf may be badly
thinned and even die in patches thus giving an appearance that adequately
describes the disease’s other name of “melting out”.
Dollar Spot (Sclerotinia homoecarpa)
is a common summer disease found on many turf species, but is most
common on Bermudagrass. This disease is found more prevalent on neglected
turf or areas that are under moisture or nutritional stress caused
by the lack of nitrogen. Humid weather with heavy dew promotes the
disease, which begins as small (2-3 inch) circular dead spots throughout
the lawn. These small spots can then grow together to form much larger
blighted turf. Fungicides are effective in controlling dollar spot,
but a good fertilization and watering program will also help in the
management of this disease.
Controlling these summer diseases is best accomplished
by keeping the turf as healthy as possible by reducing stress conditions:
- Avoid excessive nitrogen fertilization (with the exception
of dollar spot).
- Water, when needed, early enough in the day so foliage
will not remain wet overnight.
- Mow regularly at proper height with a sharp mower only
when the turf is dry.
- Be prepared to apply fungicides according to label recommendations
if climatic conditions favor disease proliferation.
Published July 4, 2005
Dr. Wayne Wells is an Extension Professor
and Turfgrass Specialist. His mailing address is Department of Plant
and Soil Sciences, Mail Stop 9555, Mississippi State, MS 39762. wwells@ext.msstate.edu
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