Dandelion, plantain, and white clover are common perennial broadleaf weeds in lawns. Broadleaf weeds in lawns can be removed manually by pulling and digging or destroyed with broadleaf herbicides.
In small areas, some weeds can be controlled by pulling and digging. This method is best accomplished after a heavy rain or deep watering. Unfortunately, pulling and digging is often ineffective on deep-rooted weeds.
In many situations, herbicides are the only practical method of weed control. Effective broadleaf herbicides include 2,4-D, MCPP, and dicamba. The most effective broadleaf herbicide products contain a mixture of 2 or all 3 of these compounds. Combination products control a wider range of broadleaf weeds than a single compound. For example, 2,4-D does an excellent job on controlling dandelions, but is relatively ineffective against white clover. MCPP, on the other hand, provides excellent control of white clover and only fair control of dandelions. Products containing 2,4-D and MCPP effectively control dandelions and white clover. Triclopyr is another broadleaf herbicide. It is typically used on hard-to-kill broadleaf weeds.
The best time to control perennial broadleaf weeds in the lawn with broadleaf herbicides is fall (mid-September through October). In fall, perennial broadleaf weeds are actively translocating carbohydrates to their roots. Broadleaf herbicides applied to the weeds will be absorbed by the foliage and translocated to the plant's roots along with the carbohydrates. This usually results in the death of the broadleaf weeds.
Broadleaf herbicides can be applied as liquids or granules. Before applying any herbicide, carefully read and follow label directions. When applying liquid formulations, potential spray drift problems can be avoided by following simple precautions. Don't spray when winds exceed 5 mph. Also, don't spray when temperatures are forecast to exceed 85ÃƒÂ»F within 24 hours of the application. Since coarse droplets are less likely to drift than fine sprays, select nozzles that produce coarse droplets and use low sprayer pressure when applying liquid broadleaf herbicides. If only a few areas in the lawn have broadleaf weed problems, spot treat these areas rather than spraying the entire lawn. Apply just enough material to wet the leaf surfaces.
Granular broadleaf herbicides are often combined with fertilizers. Apply granular broadleaf herbicides and fertilizer-broadleaf herbicide combinations when the weed foliage is wet. Wet leaf surfaces allow the granules to stick to the foliage, permitting herbicide uptake. (Broadleaf herbicides are absorbed by the plant's foliage, not their roots.) Apply granular products in the early morning when the foliage is wet with dew or irrigate the lawn prior to the application.
To insure adequate leaf surface and herbicide absorption, don't mow the lawn 2 or 3 days before treatment. After treatment, allow another 2 or 3 days to pass before mowing. This allows sufficient time for the herbicide to be translocated to the plant's roots. To prevent the broadleaf herbicide from being washed off the plant's foliage, apply these materials when no rain is forecast for 24 hours. Also, don't irrigate treated lawns within 24 hours of the application.
Broadleaf herbicides are important tools in controlling weeds in the lawn. However, good cultural practices are also important. Proper mowing, fertilization, and other sound management practices should help establish a thick, healthy lawn. A dense stand of grass provides few opportunities for unwanted weeds. Good cultural practices, along with an occasional application of a broadleaf herbicide, should effectively control most broadleaf weeds in the lawn.
This article originally appeared in the August 24, 2001 issue, pp. 106-107.