St. Augustine Decline (SAD). Also called Take-all
Patch.
Circular patches .5' ? 3' diameter; initially yellowish;
gradually turning brown and thinning; roots darkened;
chlorotic leaf blades may develop next to green
shoots at margins of diseased area; roots brown
and without feeder roots and root hairs.
St. Augustine Decline (SAD) is a virus causing
a chlorotic mottling or stippling of St. Augustinegrass
leaves. St. Augustinegrass and centipedegrass are
the only turfgrasses that the virus is known to
affect. The virus is widespread in Texas and has
been reported in Louisiana and Arkansas.
In the early stages of infection, St. Augustinegrass
leaves show a chlorotic mottling or stippling. As
the mottling progresses, leaves develop a chlorotic
appearance. Usually 3 or more years after the early
symptoms are observed St. Augustinegrass becomes
weakened to the extent that bermudagrass invades
the lawn.. Also, grass infected with SAD and growing
under shade or other stress conditions will begin
to thin out and be replaced by weeds.
St. Augustinegrass infected with SAD is also slower
than healthy grass to recover. In the spring following
an unusually cold winter, much of the diseased St.
Augustinegrass does not recover.
Lawns infected with SAD will respond to fertilization,
but the symptoms remain. Early fall and late spring
applications of complete fertilizer and summer applications
of iron will help maintain good color of SAD infected
lawns.
Early stages of SAD are often confused with iron
chlorosis, but the two can be readily distinguished.
Leaves showing chlorosis caused by iron deficiency
are either uniformly yellow or show characteristic
yellow stripes parallel to the mid-vein of the leaf.
Iron chlorosis also appears first in the new, or
young leaves; whereas SAD produces the mottling
in young and older leaves. Iron chlorosis is readily
corrected by a foliar application of iron sulfate
or iron chelate.
The SAD virus, like all viruses, is a microscopic
particle found inside the cells of St. Augustinegrass.
Inside the plant cell, the virus reproduces and
spreads to other cells throughout the plant. As
more and more cells become infected with the virus,
the vigor of the plant is reduced, rendering it
more vulnerable to other diseases and environmental
stresses.
Control
The SAD virus is mechanically transmitted by mowing
equipment, edgers and other tools. Mowing companies
that mow several lawns with the same equipment can
transmit the virus from an infected lawn to a healthy
lawn. Cleaning the mowing equipment with steam or
a 10% chlorox solution will help prevent the spread
of the virus.
However, the best control for the virus is to introduce
resistant varieties of St. Augustinegrass into the
lawn. Presently, Floratam, Floralawn, Raleigh and
Seville are SAD-resistant varieties of St. Augustinegrass.
Simply plug the resistant variety into the existing
lawn on 2' ? 3' centers. The resistant grass will
crowd out the diseased grass over a period of a
year or more. There are no chemical controls for
SAD.
