   Lawn Weed Control - July 5, 2006 Jeff Schalau, County Director, Associate Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Maintaining a healthy, vigorous grass stand is the best way to prevent and reduce weeds in lawns. However, totally weed-free lawns are rare, even when herbicides are used. Herbicides can be an effective tool, but can also be harmful surrounding landscaping in addition to the costs, labor and equipment needed to apply them. Striking a balance between healthy turf and tolerance of a few weeds is the key to having an attractive, functional lawn. Healthy turf is maintained by proper irrigation and following recommended guidelines for fertilization, mowing height, and other cultural practices such as dethatching and aerification. The first step is identifying the grass being grown and whether it is a warm or cool season species. Warm season species go dormant (turn brown or straw-colored) in the winter months while cool season species are green year-round. Warm season species are fertilized and renovated in the summer months. Cool season species are fertilized in the spring and fall and renovated in the fall. Cooperative Extension has turf maintenance calendars for the major grass species grown in our area. Once weeds have become established in lawns, a strategy should be designed that makes sense for you and your household. The strategy should address the vigor of the turf, its maintenance and irrigation, and whether or not you will use herbicides. Most lawn problems are human-caused: poorly adapted turf species; inadequate or uneven irrigation; improper mowing (scalping); improper timing or lack of fertilization; soil compaction caused by various activities/practices; and other factors. If you can identify and correct these factors, your weed problem may begin to correct itself without the use of herbicides. Correct identification of the weed species present will also help determine the appropriate course of action. Annual weeds are usually easier to control than perennials. If multiple species are present and some of them are perennials, then herbicide treatment may be appropriate. If one or two annual species are present, you may consider hand-pulling and increasing turf vigor through cultural practices. Mowing off seed heads and discarding grass clippings is one way to reduce weeds. Common annual weed species are: puncturevine, crabgrass, annual bluegrass, some clovers, knotweed, purslane, chickweed, and spurge. Common perennial weed species are: field bindweed, dandelion, curly dock, bermudagrass (in cool season lawns), silverleaf nightshade, and nutsedge. The chemicals most readily available to homeowners for selective post-emergent control of broadleaf weeds include: 2,4-D; 2,4-DP; MCPP; MCPA and dicamba. They are available singly and in various combinations with each other. Combination products are recommended for difficult-to-control weeds or when several weed species are present in the lawn. All are available in liquid formulations (sprayable) and often in granular formulations (generally with a fertilizer) that can be applied with a drop or broadcast spreader. Read product labels before purchasing to determine weed species controlled by various products. Post-emergent herbicides can also be used on annual grasses after they germinate and begin to mature. The most commonly sold type, called MSMA (monosodium methanearsonate), is often sold under trades names like "Crabgrass Killer." They are most effective against young seedling annual weeds and can be applied only as a spray. In mature, older landscapes, roots of trees and shrubs often occur throughout the entire lawn area. Do not make more than two herbicide applications per growing season on lawns with trees growing in them. Two applications are probably unnecessary for most lawns. Specifically, dicamba may accumulate in the soil with frequent or extensive use and may result in damage to trees, shrubs or other ornamentals. Remember that pesticides are tools that may be used to accomplish identified objectives. Choose whether or not to use them by assessing other weed management options including cultural practices and mechanical (direct) control. Use all pesticides selectively and carefully following label directions. Lawns are functional parts of urban/suburban landscapes, and when appropriately placed and sized, provide unique outdoor living spaces for people and pets. They can also help conserve energy and, most of all, are meant to be enjoyed. Conversely, when lawns are not serving useful functions, you may want to consider removing them to conserve water and reduce maintenance headaches. 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/. |