Control of Broadleaf Weeds in the Lawn

A well maintained lawn is an integral part of an attractive home landscape. Unfortunately, dandelion, plantain, and other perennial broadleaf weeds can become problems. When broadleaf weeds invade lawns, mechanical and chemical measures can be undertaken to remove or destroy the weeds.

In small areas, some weeds can be controlled by pulling and digging. This method is best accomplished after a good 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, MCPA, dicamba, and triclopyr. The most effective broadleaf herbicide products contain a mixture of 2 or 3 of these herbicides as no single compound will control all broadleaf weeds.

Fall (mid-September through October) is the best time to control perennial broadleaf weeds in the lawn with broadleaf herbicides. In fall, perennial broadleaf weeds are transporting food (carbohydrates) from their foliage to their roots in preparation for winter. Broadleaf herbicides applied in fall will be absorbed by the broadleaf weed's foliage and transported to the roots along with the carbohydrates, resulting in the destruction 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 85'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. When spraying, keep the nozzle close to the ground. 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. Broadleaf herbicides are absorbed by the weed's foliage, not its roots. To be effective, the granules must stick to the weeds and the herbicide absorbed by the weed's foliage. 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 3 or 4 days to pass before mowing. This allows sufficient time for the broadleaf weeds to absorb the herbicide and translocate it to their 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 produce 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.

By Richard Jauron, Department of Horticulture
Source: Department of Entomology, Iowa State University