   Bermudagrass Control - May 27, 2009 Jeff Schalau, Associate Agent, Agriculture & Natural Resources University of Arizona Cooperative Extension, Yavapai County Bermudagrass (Cynodon dactylon) is a plant that can be grown intentionally as a turfgrass or livestock forage. It has also become a serious invasive weed. Bermudagrass was introduced from Africa in 1751 and is widely spread throughout the southwest and southern United States. It is found in most areas of the Verde Valley invading gardens, landscapes, orchards, roadsides, vineyards, and industrial areas. Bermudagrass is a low-growing, wiry perennial that has two types of shoots: aboveground stolons and belowground rhizomes. The stolons and rhizomes are capable of rooting in the soil, thus creating new plants as they grow out from the original plant or when they are cut and left on moist soil. In areas where the soil has not been disturbed, rhizomes are shallow (1 to 6 inches). But where the soil has been spaded or irrigated, the rhizomes may be deeper than 6 inches. The stems root at the nodes in moist soil. The flowering stems are upright with three to seven spike-like branches usually originating from a single whorl on the tip of the stem. Bermudagrass is not an easy weed to control. Herbicide application is effective but requires careful timing and usually, more than one application. There are two basic types of herbicides that can kill mature bermudagrass, nonselective herbicides that kill most plant species and grass-selective herbicides that only kill plants in the grass family. Glyphosate is a nonselective herbicide that kills plants by translocating down into the root system, in addition to killing top-growth. For glyphosate to be most effective it must be applied to bermudagrass that is vigorously growing, not drought stressed, and has lots of leaf surface (do not mow the weed for 2 to 3 weeks before treating). The best time of the year to apply glyphosate is during late summer when the plant is storing food in the roots. However, application during the summer months can be effective - it must be actively growing. You should wait seven days after applying to mow or cultivate the bermudagrass. A second or third application may be required to completely kill well established stands. Be sure to follow label directions on all pesticides. Where bermudagrass has invaded broadleaf shrubs and groundcovers, there are grass-selective herbicides which contain one of the following active ingredients: sethoxydim, fluazifop, or clethodim. These products kill bermudagrass (and other perennial weedy grasses) and not affect broadleaf plants. Early spring is the best time to apply a grass-selective herbicide. For best control with these herbicides, make the first application in spring when new bermudagrass growth is less than 6 inches in length, then re-apply the herbicide before the regrowth reaches 6 inches again. Additional applications on regrowth may be needed through the spring and summer. Bermudagrass can also be managed non-chemically with a persistent program of removal, or over large areas by cultivation and by withholding water during the summer to desiccate the stolons and rhizomes. These non-chemical methods are more work and less effective than herbicides. However, many gardeners are not comfortable using herbicides and other chemicals. Black polyethylene sheets placed over established bermudagrass prevents sunlight from reaching the plant and can be an effective control. Mow and irrigate the grass, place the plastic over the plants, and leave it for at least 6 to 8 weeks in summer. Placing plastic over bermudagrass in winter will not control it. Be sure that the plastic remains intact without holes, or bermudagrass will grow through the holes and survive. Clear plastic sheets (solarization) are also effective for eradication of bermudagrass plants and seed if it is applied during periods of high solar radiation. In Arizona, this period is during June to August. Before applying the plastic, closely mow the bermudagrass, remove the clippings, and water the area well. It is not necessary to cultivate before solarization, but a shallow cultivation may improve control. Place clear, ultraviolet (UV) protected polyethylene over the area. The plastic should extend roughly 2 feet beyond the bermudagrass stolons to make sure the infested area is covered; it must be maintained intact for 4 to 6 weeks. After solarization, do not cultivate the area deeper than 3 inches to avoid bringing weed seed into the upper soil layer. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at cottonwoodmg@yahoo.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/. |