Bob Mugaas, University of Minnesota Extension Educator
When trying to select the ‘right’ weed control product, consumers are often confronted with a bewildering array of possibilities at retail gardening outlets. This prompts the honest question of ‘Which one of these products should I choose?’ Likewise, this question can have a variety of responses depending on what weeds are being targeted. This could easily be the topic of several articles.
However, there is one word of caution that is worth noting. Nonselective weed killers, that is, those that will kill all green vegetation, should not be used to treat weeds in lawns and expect the lawn not to be damaged. The result will end up like pictured where all the plants that contacted the herbicide, including the lawn grasses are killed leaving small to large patches of brown dead grass. These will now need to be reseeded or resodded since none of the grasses in these areas will come back. The two most common ingredients in these types of herbicides are glyphosate (e.g., Round-up, Kleen-up, many others) and glufosinate – ammonium (e.g., Finale). These should not be used to treat weeds in lawn areas unless the desire is to kill both the existing grass and weeds such as might be done before installing a new lawn.
Photo 1: Lawn damage resulting from a non-selective herbicide application. Bob Mugaas
For more information on homeowner available herbicides and how to go about choosing an appropriate weed control product, see the article on weed control in the May 15, 2008 Yard and Garden Newsletter.
July often signals the time to be extra careful when using weed control products as lawn grasses can be injured and/or weeds not controlled very well. The reason, high temperatures accompanied by often dry conditions. This puts our lawn grasses under stress and often slows the growth of both weeds and grasses. Product label directions will usually give specific temperature ranges for when their product should and should not be used. It is important to follow those directions exactly not only because it will minimize the chances for injury to desirable lawn grasses but it’s a violation of federal law to use the product in ways that are inconsistent with its label. Also, the return of cooler temperatures and usually more rainfall later in the summer is usually a much better time to control perennial broadleaf weeds. Unless absolutely necessary, postpone control of these weeds until later in the season.