I’ve received as many calls on recommended fertilizer rates for home lawns than I ever have and this was in spite of all of the rain fall. It’s just something about early spring that motivates home gardeners to want to fertilize their lawns. As you may recall, many times I have repeated the LSU AgCenter’s recommendations that the first application of fertilizer on lawns should be around the first or second week in April. This will allow time for the soil temperature to heat up and the root activity of warm season lawn grasses to increase so that the nutrients required for shoot and root growth will be absorbed. Applying fertilizer too early will stimulate brown patch disease in primarily St Augustine lawns that has a history of this disease, especially if this rainy weather pattern persists into mid spring. A couple of applications of a fungicide to address brown patch disease may help to slow it down, but if it continues to rain and night time temperatures are relatively cool, it could be an uphill battle. This is all the more reason to not fertilize too early, but rather think about targeting areas of your lawn that have weed problems.
Once our daytime temperatures average 60 degrees or above, herbicides like Ortho Weed B Gon/Weed B Gon Max and Fertilome’s Weed Free Zone are effective. Once the daytime temperatures reach the mid – high 80’s the injury from these two herbicides increases on lawn grasses. Herbicides can still be applied, but you’ll need to apply Celsius or MSM Turf, both of which are formulated to decrease the likelihood of turf injury occurring under high temperatures, and both of which can be applied during the summer months.
Virginia buttonweed is a very serious weed in many lawns in South Louisiana. It is a thick mat forming perennial broadleaf that comes back year after year once established. Leaves are opposite and flowers are white star shaped with 4 lobes. Virginia button weed produces by heavy seed production and stem fragments, both of which can start a new plant. No one application of any herbicide is going to control it. It’s going to take persistence with several applications of herbicides beginning in mid – late April through October. Apply Weed B Gon/ Weed B Gon Max or Weed Free Zone in the mid – late Spring (April & May) every 10 – 14 days and Celsius or MSM Turf every 4 – 6 weeks through the summer months from June until October. Some gardeners have sacrificed certain areas of their lawn by applying a herbicide containing glyphosate commonly known as roundup with spot treatments. Others have hand removed large mats of Virginia button weed and bagged or burned it. Virginia button weed can be spread by seeds floating in water and by lawn equipment moving from lawn to lawn. It may be a good idea for lawn maintenance crews to rinse lawn mowers between sites to remove seed and fragment of plants to reduce the spread of this weed that can be devastating to lawns. Nature has designed this weed to survive, it’s very low growing, it’s drought tolerant, it thrives in low or poorly drained areas, and it will out compete lawn grasses. So that is why especially if this weed is in a St Augustine lawn, the lawn should never be mowed shorter than 3 inches, or the advantage goes to the Virginia button weed.
Another broadleaf weed though not as invasive or competitive with lawns grasses as Virginia button weed is a winter annual called Spur weed or Lawn Burweed, which is a low growing resembling miniature parsley. It reproduces by seed and is presently in lawns. It has sharp spines or stickers located in the leaf axils and are injurious to humans when stepped on with bare feet as it approaches maturity. It can be especially distressing to young children. Many people here in south Louisiana refer to these as sticker weeds and as the temperatures rise, it begins to mature reaching a height of 2 – 3 inches or more. Now is the time to control it. If you choose to dig it up do so now!! If you choose to apply a herbicide, apply one of the 4 way blends such as Weed B Gon or Weed B Gon Max or Weed Free Zone. The key is to control it before it matures. It will naturally begin to mature and decline with high temperatures because it is a winter annual, but if it is allowed to persist into late April and into May, it may be too late to apply a herbicide because by then the sharp spines will already have formed and even though you kill it what will remain is a dead plant with sharp spines which can still be injurious and painful. Control it now!!
Gerald P. Roberts
Horticulturist/Master Gardener Program Coordinator
LSU AgCenter, 1010 Lafayette Street, Suite 325, Lafayette, LA 70501 GRoberts@agcenter.lsu.edu Office (337) 291-7090 / Fax (337) 291-7099