Newspaper article...
Steamed
About Lawn Diseases?
By
Jane Morse, UF/IFAS Extension Agent
Chinch
bugs may be the best known lawn pest, but there are diseases that are pests
too. Humid, sticky, muggy and wet -
welcome to the dog days of summer in Florida. High temperatures and lots of rain and
moisture are the perfect combination for fungus to thrive and infect our lawns.
St.
Augustinegrass is susceptible to three major fungal attacks during this time of
year, namely Grey Leaf Spot disease, Phythium Root Rot and Take-all Root Rot.
Gray Leaf Spot can slow growth, thin established lawns and kill large areas of the
lawn during hot, humid and wet weather usually from May through September. The easiest way to spot the disease is to
look for an oblong leaf blemish that has a dark edge with a center that is a
gray color. Disease occurrence can be
reduced by only watering in the early morning hours just before sunrise. The longer the leaf blades stay wet the more
likely they are to become infected. If
we are getting rain every few days then there is probably no need to apply more
water.
It
is important to minimize stress and avoid excessive flushes of lush rapid
growth during the rainy season. Applying
Atrazine to the grass is stressful, so timing is important. Once temperatures get above 85 degrees F
avoid applying this herbicide. Consider
spot-treating problem areas and make sure the grass is being mowed at the
proper height.
Phythium Root Rot can appear any time of year, but it is always associated with wet soil
conditions. Excessive watering, abundant
rainfall or poor drainage conditions can all promote this disease. Since the roots are affected, the symptoms on
the leaves are due to what is happening to the root system. There is a general decline in lawn quality. Small or large areas become yellow, light
green, or brown in color and become thin.
The lawn will seldom die from this root rot. Roots will appear thin with few root hairs
and will be discolored, but not black and rotted.
To
prevent the disease, improve drainage and reduce watering the lawn, especially
before periods of high rainfall. Avoid
watering schedules that keep the soil wet.
During periods of high rainfall mow grass at the proper height and mow
frequently enough to only remove one-third of the leaf blade per mowing. Apply a fertilizer that has an equal amount
of nitrogen (N) and potassium (K).
Take-all Root Rot is naturally present on the roots of warm-season grasses. The trigger for disease development is high
rainfall and stressed grass. The disease
is normally seen during the summer and early fall months, especially during
periods of prolonged rainfall. Since
this is a root disease, the early symptoms can only be seen on the roots. If the grass is only slightly stressed you
may never see the above ground symptoms of this disease. Irregular, yellow or light green patches
ranging in diameter from a few inches to a few feet will be the first above
ground symptoms. Once you do see above ground symptoms on the grass, the roots
have been under attack for 2-3 weeks or longer and they will be thin and
off-white in color with isolated black lesions. As the disease progresses the
roots will become short, black and rotted.
The grass stolons or rhizomes (runners) may have black lesions and may
even begin to rot. Entire plants will
die and can lead to large dead patches.
This disease can easily be mistaken for chinch bug damage, so the first
step in any pest management program is to identify the pest (weed, insect or
disease).
Once
above ground symptoms are seen this disease is very hard to control, so
prevention is the key. The grass must be
mowed at the correct height and mowed frequently enough so that only one-third
of the leaf blade is removed each time it is mowed. Scalping is very stressful because it damages
the growing point. Apply equal amounts
of slow-release nitrogen and potassium.
Avoid nitrate-nitrogen products.
Micronutrients should be applied as a foliar (leaf) feeding and they
should all be in the sulfate form. If
the root system is badly damaged the roots will not be able to get their
nutrients from the soil so frequent foliar feeding of all nutrients (N, P, K
and micronutrients) in small amounts will be necessary (remember to follow
local and county ordinances). Avoid
using herbicides on St. Augustinegrass as this is a stressor. Learn how to manage the turfgrass to limit
weeds so herbicide usage can be reduced or eliminated.
