AMES, Iowa — Homeowners know a well maintained lawn is an integral part of an attractive home landscape. Iowa State University Extension and Outreach horticulturalists share mechanical and chemical measures that can be undertaken to remove or destroy broadleaf weeds when they invade lawns. To have additional plant and garden questions answered, contact the ISU Hortline at 515-294-3108 or firstname.lastname@example.org.
Fall (mid-September to early November) 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. Spring applications are generally less effective than fall applications.
Effective broadleaf herbicides include 2,4-D, MCPP, MCPA, dicamba, triclopyr, and others. The most effective broadleaf herbicide products contain a mixture of two or three herbicides as no single compound will control all broadleaf weeds. Broadleaf herbicides can be applied as liquids or granules. Before applying any herbicide, carefully read and follow label directions.
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 miles per hour. Also, don’t spray when temperatures are forecast to exceed 85 degrees Fahrenheit 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 two or three days before treatment. After treatment, allow three or four 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.
Ground ivy (“creeping Charlie”) in lawns can be controlled with broadleaf herbicides. Products that contain 2,4-D or triclopyr are most effective. 2,4-D is an active ingredient in many broadleaf herbicide products. Triclopyr can be found in Ortho Weed-B-Gon Chickweed, Clover, and Oxalis Killer for Lawns and several other products. In Iowa, herbicide applications should be made between mid-September and the first of November. Two applications are necessary to effectively control ground ivy. The first application should be made in mid to late September, the second a month later.