The best defense for weed management is a thick, well-managed turf. A vigorous turf will successfully compete with weeds for light, nutrients, and water. Weeds become established most readily in thin, weak stands of turf. Spraying weeds by itself does not usually produce satisfactory, long-term results. Although herbicides can be used in integrated weed control system, proper management can do much to encourage a dense, vigorous turf and discourage weeds.
Herbicides are available to control most turf weeds. Care should be used when applying any pesticide for weed management. Always read and follow label directions. Improper use can result in poor weed control, turf injury, or injury to sensitive ornamental or garden plants.
Preemergence herbicides are applied to the turf before weeds germinate. They are used primarily to control annual grasses such as crabgrass, but also may control certain annual broadleaf weeds. These products should be applied several weeks before weeds germinate for best weed management. To control most annual grasses, apply preemergence herbicides when soil temperature exceeds 50°F. A second application is sometimes needed to provide season-long control. Preemergence herbicides are sprayed once the weed has emerged and are applied to the foliage of actively growing weeds. Most postemergence herbicides control broadleaf weeds, and some are available for grasses.
There are several factors which influence the effectiveness of postemergence herbicide applications. Control is easiest to achieve when the weeds are small, healthy, and actively growing. As the weeds age, changes in the leaf surface, growth habit, and physiological function occur. These changes result in reduced herbicide uptake and translocation.
Avoid mowing for several days before and after postemergence herbicide application. Mowing before application reduces the amount of weed foliage available to intercept the chemical and causes stress which reduces herbicide uptake. Mowing after application may remove the treated portion and prevent translocation to the roots.
Do not apply postemergence herbicides to turfgrass and weeds under heat or drought stress. Injury may occur to the turfgrass and weed control may be less effective. Water the turf thoroughly before application to assure that the weeds are actively growing. Unlike the preemergence herbicides, don’t water for several days after application. Watering can wash the herbicide off the plane. Also, avoid spraying if rain is expected within 24 hours.
Many postemergence herbicides for the control of broadleaf weeds are very volatile and may injure sensitive plants in the area. Care should be taken to only spray when the wind is 5 mph or less, and the air temperature is less than 80°F. Postemergence broadleaf herbicides are either applied early in the spring (April-May) or in the fall prior to the first frost.
Herbicides are a useful tool for controlling weeds, but they only provide short-term relief. The best approach is to use an integrated system which utilizes proper mowing, fertilizing, and irrigation management to establish a vigorous turf.
R.E. Gaussoin and A. R. Martin. (1997). Turfgrass Weed Identification and Prevention. In F. Baxendale, Ph.D., & R. Gaussoin, Ph.D., Integrated Turfgrass Management for the Northern Great Plains (pp. 116-117). Location: Nebraska
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