A common question we receive this time of year is “Is it too late to put on a preemergence herbicide to prevent summer annual weeds?”
It depends on what weeds are common in your yard. Crabgrass starts germinating at 53 to 58 degrees Farenheit and according to an Oconee County site of the Georgia Automated Environmental Monitoring Network ( www.georgiaweather.net), the 2” soil temperature is 52.8 degrees Farenheit while the 4” temperature is 53.9 degrees. So depending on the sunlight exposure in your yard you might still be ahead of crabgrass germination or a few seeds could have already germinated.
There are a few other summer annual weeds but crabgrass is our biggest summer enemy in home lawns.
Spring green up of our warm season lawns such as bermuda, zoysia, and centipede occur at the same time that winter annual weeds rapidly grow and flower.
These weeds compete with the turfgrass for moisture, nutrients , space and most importantly sunlight. The mats of weeds rob sunlight when the grasses are exhausting their supply of energy stored in roots. Therefore the grass cannot produce more energy through photosynthesis due to a lack of sunlight. The end result is you have a weakened, thin stand of grass that is more likely to be invaded by crabgrass and other warm season weeds. The winter annual weeds are flowering now and preparing to lay down a crop of seeds to start the cycle over again next fall.
Though my yard and many across Barrow County look horrible now due to the presence of flowering winter annual weeds, killing these weeds with a post emergence herbicide now could harm your grass or at the least delay green up 2-6 weeks. My theory is use your lawnmower set at a low setting and scalp your lawn to erase the sight of these weeds now. Yes the weeds are persistent and will regrow to produce a few flowers and thus seed heads but your problem will be lessened.
Wait until your warm season lawn is green before you fertilize. Fertilizer can improve the thickness of your lawn and reduce the need to apply weed killers.
However, fertilizing too early or using a weed and feed product in early March can promote rapid growth of the grass which can be harmed by a late frost thus further weakening your lawn.
Take a soil sample before your grass greens up. This can tell you what nutrients are needed and how much to apply.
The first application of fertilizer to bermuda or zoysia should occur no earlier than mid to late April while early May is better for centipede.
Fescue, being a cool season grass, should be fertilized now and then again very lightly in early May. Do not fertilize fescue in the summer but rather let it go partially dormant. Hot, dry weather tends to make fescue slow down. Fertilizing it again lightly in September and November will give it dark green color and increase winter hardiness.
Do not make routine applications of insecticides or fungicides to your lawn unless you have an outbreak of a pest. This is wasteful and potentially dangerous to the environment. Proper fertilization and regular mowing can go a long way to making your lawn look better and preventing the need for pesticides.
Keep your lawn mower blade sharp and always wear sunscreen.
Britt West is the extension agent for Barrow County. You can reach him at firstname.lastname@example.org.