If you recall in last month’s article I briefly mentioned brown patch disease and weed control in home lawns. Well with the additional rainfall following the publication of last month’s article, be prepared for brown patch disease problems in home lawns, especially those areas of the lawn that may not be well drained or those areas that receive poor air circulation such as an enclosed yard or areas in the shade. Additionally, be prepared to aggressively control broadleaf weeds which will continue to thrive with the abundance of moisture. Brown patch will appear as an irregular circle of dead or dying grass. Also remember to not wait to control broadleaf weeds which should be done before daytime temperatures reach the high 80’s or 90’s.
Lawn grass injury will occur with the application of either of the common homeowner herbicides such as Ortho Weed B Gon or Fertilome’s Weed Free Zone when daytime temperatures are consistently above 87 degrees. Once daytime temperatures consistently reach 87 degrees or above, broadleaf weed control should consist of MSM Turf or Celsius both of which are effective in controlling broadleaf weeds while greatly lowering the risk of turf injure due to high temperatures.
The popularity of home vegetable gardens has given rise to more gardeners who deal with fungus disease problems especially during and following rainy weather patterns. One of these is a fungus disease called “Southern Blight.” Tomatoes and peppers are two of the most popular crops affected by Southern Blight or sometimes referred to as Southern Wilt.. During periods of high moisture plants begin to wilt and die. If plants begin to wilt, look for a white cottony type growth near the stem of the plants at or just above the soil line. Additionally there may be small tan or brown round structures resembling mustard seeds, which are the fruiting bodies of the disease. If that is the case, then, pull those plants and eliminate them. Don’t plant similar plants in that spot, instead turn the soil over and bury the area around the infected plants six-to-eight inches deep. Consider planting a grass type crop like sweet corn in that area next year.
There are no fungicides to address the problem once the infection is established, and under high moisture conditions it’s debatable if a preventative fungicide is effective. Many older gardeners at transplanting will protect the lower stems of tomatoes and peppers by wrapping a three-to-four inch wide strip of aluminum foil on the stem of peppers and tomatoes as a physical barrier to prevent infection. Typically since Southern wilt infects the lower stem at or just below the soil line, the aluminum foil is wrapped where one inch extends below the soil line and two inches above the soil line. This appears to be effective in decreasing infection.
Because of the wet cool conditions we’ve been experiencing, expect to see the leaves of several species of oaks become infected with oak leaf blister. While all species of oaks are susceptible and can be severely infected, live oaks are the least affected. Early symptoms resemble bright green spot which can cause leaf curl and defoliation. As the infection ages the spots become tan and eventually brown. While no permanent damage occurs to the tree as a result of oak leaf blister it can be very unsightly and alarming to gardeners. Even though there are fungicides labeled to control oak leaf blister it is not practical for a couple of reasons. One of which is by the time visual symptoms occur the infections have already taken place. The second reason is it is not practical for homeowners to invest in the equipment necessary to spray large trees. The trees usually recover without any permanent damage.
Every spring I get calls from gardeners who ask me if there are any herbicides labeled or effective to control grassy weeds in St Augustine or Centipede lawns. Remember we’ve talked in the past about controlling broadleaf weeds in lawns but grassy weeds are a different story. Controlling broadleaf weeds in lawns are easier than controlling grassy weeds in lawns. There is a wider selection of herbicides labeled to control broadleaf weeds in lawns than there are herbicides to control grassy weeds in lawn. There is only one herbicide that is available to homeowners that will give control of any grass in St Augustine grass, which is called MSM Turf, yes the same MSM Turf that can been applied to lawn grasses once the temperatures reaches the high 80’s and into the 90’s without injury to the lawn grass. This is the same MSM turf that is also effective in controlling broadleaf weeds, but it also controls Bahia grass in St Augustine lawns if Bahia grass is a problem. However, for Centipede lawns there is a better option for controlling grassy weeds, such as any herbicide containing “sethoxydim” the brand name is “Vantage” or “Poast”, which will be effective controlling grasses in Centipede lawns.
Sedges can also be a problem in landscape beds and lawn grasses, both purple and yellow nutsedge (which is also commonly called coco grass or nut grass , but they’re not grasses, they are sedges). There is a herbicide called Sedgehammer, with the active ingredient “Halosulfuron” which is very effective on both yellow and purple nutsedge!! It can be applied to landscape beds containing established woody ornamentals. It is applied directly to the nutsedge avoiding contact with woody ornamentals leaves or stems. It is not labeled for annual flower beds!!! It can also be applied to established lawns to control sedges!! To control grasses in landscape or flower beds fortunately there are a couple of very effective grass herbicides, one is Sethoxydim also called Poast, and Fluazifop also called Grass B Gon. There may be other brand names available but as long as the active ingredient is Sethoxydim or Fluazifop it will be effective. These herbicides will control grasses only, not broadleaf weeds.
Because this has been a wet spring, I know weed problems are going to be a problem. I tried to provide information which will allow you to make decisions not only in your gardens but also in advising others. It must always be emphasized that it is very important to read the label and follow directions before using any Pesticide!! It is not only about safety (protecting yourself, others, pets, and the environment), but also about following recommended rates to increase effectiveness and avoid injury to desirable plants.
Remember “The Label is the Law!”
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