My St. Augustine grass is... - Ask Extension
My St. Augustine grass is developing yellow places and I put some sulphur on the places and it seemed to help but the places are getting larger. I d...
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My St. Augustine grass is... #152795
Asked September 15, 2013, 8:40 PM EDT
My St. Augustine grass is developing yellow places and I put some sulphur on the places and it seemed to help but the places are getting larger. I don't believe it is lack of water. What can I do?
Parker County Texas
Expert Response
St Augustine lawn turn yellow sometimes from a lack of
fertilizer but can be caused by one or several of these reasons:
1.
Leaching
nutrients from soil from too much water either rain or irrigation
Solution is to cut back on irrigation
frequency. Check the irrigation system to make sure it is working properly. Set
the controller to cycle and soak, which means applying the same amount of water
but with multiple start times. Check your owner’s manual or call the
manufacturer’s customer service to find out how to do this.
We do not usually recommend fertilizing
during water restrictions, particularly now that the temperature is so high.
But if you use a pelleted slow release fertilizer and apply the fertilizer
either early in the morning on the day you are allowed to water. Water that
morning for a short time and then again that evening for a short time. This
will start the process of watering the fertilizer into the roots zone.
2.
Compacted soil will create such tight soils that
water and fertilizer never gets down to the root zone. The heavy clay soil in
Tarrant county get compacted from regular use – mowing, watering and rain but
kids and pets playing can add to the compaction. After construction, soil is
very compacted. Aerate the lawn and then spread about ½ inch of compost across
the lawn before the aerated holes fill in with expanding clay. Water in the
compost. The air in the roots zone and the nutrients in the compost will help.
You may want to do this again in the fall.
3.
Lawn diseases may be the cause but usually lawn
disease problem is not an entire lawn. Lawn diseases usually start in one spot
and then spread.
4.
Misapplication of weed killer.
Take-all Root Rot of Turfgrass
Take-all
root rot is a serious disease caused by the soil fungus Gaeumannomyces graminis var. graminis. Take-all root rot
causes brown, dead areas to develop in turfgrass. The disease was first
described in Texas in 1991 on St. Augustinegrass. Since then, it has been
confirmed on bermudagrass (where it is often called bermudagrass decline),
zoysiagrass and centipedegrass.
Symptoms and
diagnosis
Symptoms of
take-all root rot often are noticed first in spring or early summer, but may
show up at any time during the growing season. The grass appears yellowish
(chlorotic) thins out in large, irregular patches 1 foot to more than 20 feet
in diameter. Individual grass blades do not separate easily from stolons
(horizontal stems). The roots of infected grass are usually short, blackened
and rotted. The stolons often can be lifted easily from the soil because of the
poor root system. Nodes may be discolored. The yellowish foliage eventually
dies and turns brown. Take-all root rot may be mistaken for Rhizoctonia brown
patch or chinch bug injury on St. Augustinegrass. If you suspect your grass has
take-all root rot, first eliminate the possibility of these other problems.
The fungus that
causes take-all root rot is common in Texas, in both diseased and apparently
healthy grass. It does not survive well in the soil without a host plant or
plant debris, such as thatch. Turfgrass often shows the first symptoms of the
disease from spring green-up through early summer, which suggests that the fungus
infects the turf grass in the fall or early spring. However, the disease can
occur at any time during the growing season, especially when the weather is
warm and moist and grass is under stress. The disease is not spread by mowers
or by normal traffic, but it can be spread by the movement of infected grass or
infested soil.
Cultural disease management
Controlling
take-all root rot (and bermudagrass decline, as it is also known) requires both
cultural and chemical practices. The first step in preventing the disease is to
take proper care of the grass, so that it grows at a moderate rate and there is
abundant microbial activity in the root zone. Good surface and subsurface
drainage is important. Turf areas that remain wet are prone to disease. Improve
drainage if necessary and fill in any depressions in the soil. Avoid over
watering. It is better to water infrequently but deeply (6 to 8 inches deep)
than to give the grass frequent, shallow waterings.
Have your soil
tested and fertilize grass on the basis of the test recommendations. Do not
apply excessive rates of nitrogen fertilizer. If possible, adjust the soil pH
in the root zone so that the pH is slightly acidic, preferably within the range
of pH 6.0 - 6.8. To help adjust pH and control disease, spread about ½ inch of
compost over the lawn in the spring and fall for several years.
Soil also should
be aerated if it is compacted.
Fungicides
If take-all root
rot or bermudagrass decline are a problem in your lawn, you will probably need
to apply a fungicide. Fall and spring are the best times to do this. The
following fungicides are labeled for the control of take-all root rot or have
been shown to be effective in research tests. Check with local garden centers
and feed stores for a recommendation.
Fungicide should
be applied in a high volume of water or watered in thoroughly right after
application.
This will ensure
that the product moves into the grass root zone rather than drying on the
leaves.
Common hose-end
applicators work well for soaking the fungicide into the root zone. Fungicides
are most effective as preventative treatments and much less effective after the
disease has become well established. However, it is usually effective to treat
diseased areas in the spring after the easily-removed, infected stolons are
raked out or lifted away. Two applications 3 to 4 weeks apart may be required.
Always read and
follow carefully any instructions and precautions on the product label.
Take-all root
rot usually becomes a serious problem only when turfgrass is under stress
because of soil compaction, temperature extremes, herbicide injury, imbalanced
soil fertility, excessive shade, improper mowing height or frequency, excessive
and too frequent watering, or any other condition that weakens the turf.
