St. Augustine Decline
Texas Cooperative Extension
Text and images copyright © Richard Duble.
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.
Description. 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- or 3-foot 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.