By John Fech

Herbicides applied to turfgrass are generally effective when they’re applied according to label instructions. Manufacturers spend a lot of time and money testing and retesting products for efficacy, as well as the potential for environmental damage before they’re released.

Failure does happen, but it usually falls into one of three categories: 

  1. improper mixing,
  2. spraying or application concerns, or
  3. environmental effects.

Other Important factors affecting the effectiveness of herbicides on turfgrass include:

  • Volatilization: Volatilization primarily involves the upward movement of the herbicide away from the turf. This occurs by a large percent of the applied herbicide turning from a liquid state to a vapor or gaseous state. There are no weeds to kill in the air, so this is a reduction in active ingredient on the turf surface. Volatilization effects can be limited by avoiding hot, windy days and choosing low-volatility ingredients in herbicide products.

  • Temperature: Most products are designed to work in moderate temperature conditions. When temperatures are cold, foliar sprays for broadleaf weeds aren’t effective. Likewise, when temps are 90 degrees Fahrenheit and above, there’s reduced effectiveness. The bigger concern with high temperatures is that the herbicide application will cause foliar burn on the turf and nearby ornamentals. Apply herbicides carefully when it’s hot.

  • Equipment calibration: Orifices get plugged and worn, and nozzles get bent or crushed. The best way to deal with this is a spray check. For boom sprayers, attach glass jars underneath each nozzle, let the sprayer run for a minute, then measure the amount in each jar. In most cases, some will have put out the right amount, some less than desired, some more than desired, and some will be plugged. For dry spreaders, mark off a 1,000-square-foot section of turfgrass. Weigh out the correct number of pounds of product to deliver one pound of nitrogen (usually 3 to 4 pounds of product) and apply it over the section. If there’s not enough in the hopper to cover the area, or there’s considerable leftover after the area is covered, then your spreader needs to be calibrated.

Follow Directions on the Label
To get the most from an herbicide, any herbicide, start by reading and following label directions. The label provides:

  • Directions for the most appropriate timing of the application.
  • Recommendations for the correct amount of water to use as a carrier.
  • Size of the mesh screen to use in the spray system.
  • Agitation requirements, if necessary.
  • Restrictions on other products that may be perceived to enhance its performance.
  • Indications for enhancement with the addition of adjuvants, crop oil concentrates or spreader-stickers.
  • Specific guidelines for the amount of the product to mix with water.
  • Possible need for circulation of the herbicide mixture through the hoses and spray tank.

John C. Fech is an extension educator specializing in turf and ornamentals at the University of Nebraska-Lincoln.

Note: This article appeared in the August issue of Superintendent magazine, another fine Moose River Media publication.