Cogongrass control varies according to the age and rhizome mat density and depth. Young infestations are usually easier to control than older well-established infestations. For newer patches, tillage can eliminate cogongrass from an area if continued during the course of a growing season. The initial tillage should begin in the spring (March through May) with an implement that inverts the soil to a depth of at least 6 inches. Perform additional tillage with a disk harrow or other appropriate implement every 6 to 8 weeks. It is important to clean all equipment on site to prevent the spread by rhizomes. Dry periods during the summer will aid in the control of cogongrass. The area can be planted to a fall cover crop and then followed the next season with perennial or annual grass or broadleaf crops. Mowing may help reduce cogongrass stands, but areas must be mowed frequently and at a low height. Monitor the site throughout the growing season; spot treat any recurring infestations with appropriate herbicides.
Tillage may not be an option on many sites such as steep slopes, established tree plantings, or around dwellings. Out of dozens of herbicides tested for significant activity on cogongrass only two, the active ingredients glyphosate (Roundupa, Glypro, Accordb, etc) and imazapyr (Arsenal, Arsenal AC, and Chopperc), have much effect on this grass. Even at high rates and using tank-mix combinations, cogongrass often regenerates within a year following a single application of either product. A minimum of two applications per year is needed, realizing that older infestations may require 2 to 3 years of treatment to eliminate rhizomes. Glyphosate has no soil residual activity. Imazapyr has both soil and foliar activity and can severely injure susceptible plant species that are planted too soon after the last treatment. Most vegetables, row crops, and ornamentals will be injured if planted with 24 months following an imazapyr application. As with all pesticides, proper handling and usage is of utmost importance and always read and follow label directions.
Cogongrass in small (less than 20 foot diameter) patches can be treated with a glyphosate solution in early fall (August through October). A 4% solution of 41% active ingredient material (5 1/3 fluid ounces per gallon of water) sprayed on the green leaves and allowed to dry for 2 to 3 hours will kill the top growth of cogongrass. Regrowth must be treated the following spring and possibly the next fall to ensure rhizome kill. CAUTION: glyphosate herbicide spray mixtures should be considered non-selective when sprayed on green tissue. Keep spray and spray drift off any desirable plants. Treat larger infestations with glyphosate using a tractor-mounted boom sprayer calibrated to deliver 10 to 15 gallons of spray solution (water + herbicide) per acre. Use glyphosate at the rate of 3 to 4 pounds active ingredient per acre. This translates into 3 to 4 quarts of herbicide per acre for the 41% active material. Replacement species should be planted in the area following the last treatment (either spring or second fall after 90% control is achieved) to suppress reinfestation. Plant crimson clover or ryegrass after the fall application of glyphosate to stabilize sloping areas through winter. Replace this cover crop with a perennial grass or with shrubs planted in a high-density pattern to provide shade over the area.
Where selective treatment is not needed, tank mixes of glyphosate (3 to 4 pounds active ingredient per acre) plus imazapyr (Arsenal 1 to 4 pints per acre) are effective. Sulfometuron (Oust XPd) at 2 ounces per acre has been shown to increase cogongrass control when applied with imazapyr, but should not be applied as a stand-alone treatment. For selective treatment of cogongrass in unimproved bahiagrass and bermudagrass turf, apply Arsenal at a rate of 8 fluid ounces per acre. In pastures, apply 8 to 48 ounces of Arsenal per acre. There are no grazing restrictions following Arsenal application. Do not cut hay within seven days of application. Burning or mowing prior to herbicide application may increase chemical effectiveness by eliminating thatch and causing the production of new growth, which better absorbs pesticide. A cogongrass fire is hot and fast. Proceed with extreme caution and careful planning and preparation. Always consult with local authorities on the rules concerning burning in your area.
To increase application effectiveness, prescribe burn, if feasible, during winter before treatment to eliminate logging debris and cogongrass thatch at harvest. Chemically site prepare with Arsenal AC (2 pints per acre) or Chopper (4 pints per acre) plus glyphosate at 4 pounds active ingredient per acre in the fall prior to planting in late winter (at least 3 months after application). This combination may be applied by helicopter and should include a suitable surfactant not to exceed 0.5%. After planting, apply herbaceous and release treatments of Arsenal AC following label guidelines over-the top of loblolly, longleaf and slash pine to control cogongrass. For loblolly pine seedlings, Arsenal AC may be applied following planting at a rate of 6 to 10 ounces per broadcast acre. A nonionic surfactant not to exceed 1/4 percent of spray solution volume can be used only for loblolly pine. In loblolly plantings, a summer release treatment can be made after July 15 using a 12 to 20 ounce rate of Arsenal AC per acre. For slash and longleaf pines use a 4 ounce rate of Arsenal AC per broadcast acre without surfactant for herbaceous control after planting. In 2 to 5 year old slash and longleaf plantations apply Arsenal AC only after August 15 with a rate of 12 to 16 ounces per acre without a surfactant. In slash and longleaf pines over 5 years of age do not treat with an over-the-top spray until after September 15 using a 12 to 14 ounce rate of Arsenal AC per acre without surfactant. Do not use surfactant with this treatment, as severe tree injury and/or mortality will result. Oust XP (1 to 2 ounces per acre) can be tank-mixed with Arsenal AC (4 to 6 fluid ounces per acre) for improved control in loblolly pine only. On well-established pines (DBH > 5 inches), apply the site prep mixture described above from August through October, taking care not to contact pine foliage. Fire is NOT recommended in standing timber unless cogongrass is in a suppressed state from prior treatment.
Rehabilitation is the most important phase of control and reclamation of land infested with cogongrass or other non-native invasive plants. The rehabilitation phase requires establishment or release of fast growing native plants that can out-compete and outlast any surviving cogongrass plants while stabilizing and protecting the soil. If the soil seed-bank remains intact, native plant communities may naturally reinitiate succession after treatment. Light seeded native species are usually present in the seed-bank while heavier seeded plants will gradually be deposited on a site by birds and other animals. In recent years, native plant seed and seedlings have become increasingly available for rehabilitation sowing and planting, but a limited number of species and absence of well-developed establishment procedures often hinder use. Georgia Forestry Commison and private tree nurseries are good sources of many species of native trees and shrubs. It is often necessary to establish fast growing tree species during the later control phase to hinder reestablishment of cogongrass. Reestablishing native grasses and forbs is equally important. These species are available from commercial nurseries specializing in native plants. Utilize local sources when possible. Seedling native plants can be also collected and transplanted from suitable field sites. Their establishment will be more challenging than the commonly available nonnative plants so often used for soil stabilization and wildlife food plots. Constant surveillance, treatment of new unwanted arrivals, and finally, rehabilitation following control are critical to preventing reinfestation on a specific site.
a Roundup is a registered trademark of Monsanto Co., 800 N. Lindbergh Blvd., St. Louis, MO 63167.
b Glypro and Accord are registered trademarks of Dow Agrosciences, 9330 Zionsville Rd., Indianapolis, IN 46268.
c Arsenal, Arsenal AC, and Chopper are registered trademarks of BASF, 26 Davis Drive, Research Triangle Park, NC 27709.
d Oust XP is a registered trademark of Dupont, Wilmington, DE 19898.