St. Augustinegrass: Drought injury
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Return to St. Augustinegrass
St. Augustinegrass - Cultivar identification
St. Augustinegrass - How much to water?
St. Augustinegrass - Shade
St. Augustinegrass - Chinch bugs
One way is to shut off the irrigation. It's often the dry season when we see how
poorly our sprinklers have been working.
The photo shows a planned curtailment,
to measure differences in drought survival among different St. Augustinegrasses. The
research was done at the University of Florida's Fort Lauderdale Center. Some of the
grasses were totally killed and others survived.
In other studies, the killing injury
(damage %, below) was closely
associated with the number of days wilt. While FX-10 and Floratam were slower to
wilt than Bitterblue and Seville, once a grass had been wilting off-and-on for a week, it
was on a death course.
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After the first week or so, St. Augustinegrass plots suffered 15% loss of canopy per
day. Plots which undewent two weeks of wilt were completely killed. Any
subsequent recovery was from stolons growing in from the sides.
Actual results which you might
experience in a lawn will vary according to microenvironment, e.g., the presence of trees,
exposure to the wind, the quality of your soil, and the condition of the turf. Other
organisms, such as nematodes, can compromise the root system and make the grass less able
to stand up to lack of water. Grass which has been fertilized recently with highly
soluble fertilizer often wilts quickly. The Fort Lauderdale experiment was done in a
microenvironment of sandy soil under full sun exposure.
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Technically, St. Augustinegrass uses only a little more water than
other, drought avoidant grasses such as bermudagrass and bahiagrass. What probably
lends to the severity of drought damage in St. Augustinegrass is the exposure of the
horizontal above-ground stems ("stolons") to desiccation. In contrast,
bahiagrass stolons are partially protected by the clasping leaf sheaths.
Bermudagrass and zoysiagrass have much of their stem material below the ground
("rhizomes"), and rhizomes are not only protected from desiccation by the soil,
but they tend to be in a semi-dormant ("hardened") condition, thus are more
resistant to desiccation.
Should the lawn be watered as soon as
it wilts? Not necessarily. There's a chance it may rain within a few days from
the first wilt, and generally it's safe to watch and wait. Wilt is typically noticed
at first in the mid-afternoon, 2 to 3 p.m. Daylight Savings Time, and the lawn becomes
turgid again by the next morning. The progression of afternoon wilt can continue for
a week or so, expanding in area and occurring earlier in the afternoon. When the
lawn still remains wilted the following morning it is on its death course. During
this progression, traffic should be kept off the turf.
Any new growth in grasses must come
from the stems. Once the stems have dried excessively, the turfgrass plant can make
no more leaves, roots, or stems.
Reference
Busey, P. 1996. Wilt avoidance in St. Augustinegrass germplasm. HortScience 31:1135-1138.