Ronald Strahan, Koske, Thomas J.
Essentially, two types of weed-and-feed herbicides are most often available to home consumers. Read the label completely for materials present and usage restrictions.
1) Weed and feeds with atrazine impregnated on a fertilizer granule are safe for St. Augustine grass, centipede grass and zoysia but not Bermuda grass. Example: Scott's Bonus S
2) Weed and feeds with 2,4-D, dicamba & mecoprop (or with Trimec) are safe for Bermuda grass and zoysia. Some manufacturers will have centipede grass on the label but almost never St. Augustine grass because of the potential for injury. Example: Ferti-lome's Weed and Feed with Trimec
If you have a St. Augustine grass yard that is not growing well and shows some yellowing foliage after a weed-and-feed application, check what kind of weed and feed you used. Also, look for 2,4-D-type symptoms on nearby shrubs.
Damages are not always lethal to the lawn, but they can be. Reversing this situation is not always possible or especially feasible for homeowners. It can definitely be very messy. The yellowing may be embarrassing but usually goes away in a few weeks. Iron chelate foliar sprays may help relieve symptoms sooner.
The LSU AgCenter and the LSU College of Agriculture