Great Plains Gardening

By Edith Koeller

May 28, 2004

Last time, I brought to your attention the control of grassy weeds in the lawn. This week I would like to consider the control of the broadleaf weeds in the lawn. CSU Extension has a fact sheet #3.100 available containing advice for the homeowner contemplating this task. I am sharing the author’s, A.J.Koski, recommendations with you in the hope it will be of benefit to you.

"The development and maintenance of a dense, healthy stand of grass is the best way to reduce the occurrence of broadleaf weeds in home lawns…the homeowner should plant the best-adapted turfgrass species and use accepted turf management practices. Even the best cared for lawns can be invaded by troublesome broadleaf weeds. The homeowner may have to resort to the careful and selective use of broadleaf weed control herbicides. A totally weed free lawn is rarely attainable, even with the use of herbicides. It is better to maintain a healthy lawn and tolerate a few weeds rather than to make many applications of herbicides in a attempt to eliminate all weeds."

"Post emergent herbicides can be used to control existing broadleaf weeds such as dandelion, clover, thistle, and bindweed; post emergent herbicides to not prevent weed seeds from germination and reinfesting a lawn. Even after the successful use of a broadleaf herbicide, it is essential to use sensible cultural practices to encourage rapid fill in of the turf, since new weeds will quickly reinfest the bare soil left open by the recently killed weeds."

"Before using a post emergent herbicide for broadleaf weed control, identify the weeds you want to control. Not all weed species are easily controlled by the same herbicides, and you may need to use a combination of two or more herbicides to obtain the desired control of specific weeds." If you have trouble with identification, the extension office will be glad to help you, as will garden center and others familiar with turf grass weeds.

"The most readily available chemicals to homeowners for selective, post emergent control of broadleaf weeds include 2,4-D, 2,4-DP, MCPP, MCPA and dicamba. These chemicals are available alone and in combinations with each other. Combination products are recommended for difficult to control weeds or when a variety of weed species is present in the lawn. All are available in liquid formulations and often in granular formations, generally with a fertilizer, that can be applied with a drop or broadcast spreader."

"All of the chemicals listed above are safe for use on Kentucky bluegrass, perennial ryegrass, tall fescue, and fine fescue lawns if the directions on the label are followed. Buffalo grass and blue grama lawns that have greened up can be discolored or injured by summer applications of products containing 2,4-D, MCPP, MCPA or dicamba; applications to dormant buffalo grass and blue grama lawns in the spring or fall are safer as long as directions are closely followed."

"It is also important to remember that weeds must be actively growing when the herbicides are applied so effective control can be achieved. This means that you should make spring applications from mid-April through early June and fall applications during the months of September and October. Herbicide applications during July and August are strongly discouraged because weed control is often poor and there is an increased risk of causing damage/discoloration to the lawns, as well as trees, shrubs, flowers and vegetable plants."

"Liquid and granular formulations of herbicides can be equally effective if they are used properly. Do not apply either if rain is expected within 24 hours of application. For best results, do not mow the turf or water for at least 24 hours following application of either granular or liquid products. Granular herbicides are the most effective if applied to the grass that is moist from morning dew, rainfall, or irrigation because the granules adhere to the wet surfaces of the weeds. Granular applications of post emergent products to dry turf generally control very few weeds. Exercise care when applying the herbicides near trees, shrubs, flowerbeds, and vegetable gardens. Drift from spray applications or misdirected application from granular products can damage or kill these plants. Tree roots can absorb large amounts of herbicides, so be careful applying any herbicide within a trees’ root zone that extends far beyond the tree’s drip line."

"In a mature, older landscape, 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, and two 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."

This fact sheet also contains a chart with common broadleaf weeds, their life cycle, the herbicide suggested for control, the timing of application and the expected control. So, if you are serious about waging war on weeds this guide will be most helpful.

Until next time…