These mixtures are perfectly fine if the product matches the situation for your lawn, but put out the wrong one and you'll be left wondering why your grass won't grow like it should, or even worse, why your lawn dies.
You can purchase fertilizer-herbicide mixtures with pre-emergence or post-emergence activity, or a combination of the two (atrazine).
I'm frequently asked about applying these products in February or March to get a jump on weed growth, but that's too soon. St. Augustine, Bermuda and zoysia should not be fertilized until around April 15, when the soil temperature usually stabilizes above 65 degrees, and centipede should not receive spring fertilization until the grass has fully greened up, usually about May 1.
If a straight pre-emergence product (no fertilizer, just herbicide) was applied about March 1, you can follow up with a pre-emergence weed and feed about three months later.
You can use one that contains atrazine that has both pre- and post-emergence activity on a broad range of weeds. There are several of these formulations available from different companies, but probably the best known is Scotts Bonus S. Atrazine in weed and feeds can be safely applied on both actively growing centipede and St. Augustine grasses.
There are other precautions needed when using atrazine-fertilizer mixtures. Do not plant sprigs within one month after application or seed within six months after application. For newly planted centipede, wait until grass has been mowed at least once.
Don't apply atrazine on or over the root zone of ornamental trees and shrubs, nor on bedding plants, flowers, or garden plants. It can be used around young trees after they have been established for two or three years.
Other weed and feed mixtures give post-emergence control. These products contain 2,4-D, MCPP or dicamba and control broadleaf weeds through foliage absorption.
Apply broadleaf herbicide fertilizer mixtures when the weed foliage is moist from a dew or rain to enhance herbicide absorption and control.
Dicamba can also be absorbed by plant roots, which increases its effectiveness. Just keep it from the roots of desirable ornamentals and young trees.
For new lawns, wait to apply post-emergence fertilizer mixtures until after a couple of mowings.
While 2,4-D mixtures can be used on all four of our warm season grasses, avoid its use on St. Augustine and centipede during spring green-up, but use it before late spring and early summer.
Last week, I found another weed and feed available to homeowners, a 17-0-7 fertilizer from Lesco called LockUp, with the active ingredient penoxsulam. It gives post-emergence weed control. The great thing about it is that it is labeled for all four warm season grasses, and it can be applied year-round (except for dormant centipede) to a wet or dry lawn.
Weeds treated with penoxsulam will stop growing almost immediately. It is a systemic herbicide, meaning it is translocated throughout the susceptible weeds. Penoxsulam disrupts the internal growth processes of weeds, resulting in the death of susceptible weeds in two to four weeks after application.
REACH SID MULLIS, THE DIRECTOR OF THE UNIVERSITY OF GEORGIA EXTENSION SERVICE OFFICE FOR RICHMOND COUNTY, AT (706) 821-2349 OR SMULLIS@UGA.EDU.