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Cultivate your weed costs
1 Jul, 2009 By: Kathy Kalmowitz Ph.D. Landscape Management[Editor’s Note: In the July print edition of Landscape Management, Dr. Kathie Kalmowitz discusses how lawn care operators can save money and satisfy customers with an integrated weed management program. Here we expand our coverage with more information from the market and technical specialist for BASF Professional Turf & Ornamentals.]
Mulch. Various mulch types complement pre-emergent herbicide programs. Mulches, including bark, wood chips, crushed rock or gravel, create a thin barrier that limits light, moderates soil temperature and physically blocks weed seedling growth.
The most effective pre-emergent herbicide applications are those made directly to the soil before mulching. If mulch is present, an application can be made on top of a thin, 2- to 3-in. layer of medium- to coarse-sized mulch material. Fine mulches aren’t recommended because they can compact and inhibit an herbicide from reaching weed seeds in the soil. Generally, if an herbicide is applied directly to any type of mulch, thorough irrigation must occur to move the product down to the soil for activation.
Post-emergent herbicides. Post-emergent herbicides control newly emerged and established weeds. They eliminate grassy, sedge and broadleaf weeds effectively, but provide poor residual control.
There are two types of post-emergent formulations: selective and nonselective. Selective herbicides have targeted modes of action that eliminate only specific types of weeds listed on the label — such as all grasses or some grasses — and some broadleaf species. Labels also list ornamentals tolerant to that product, meaning. For sedge control, the product must specifically state this weed type or it won’t control it.
Nonselective postemergent herbicides eliminate many weed species, but some can injure ornamental plants severely. To avoid this, nonselective applications should be limited to spot treatments or directed around, but not over the top, of desirable plants.
Post-emergent herbicide activity to the target weeds is classified as systemic or contact. Systemic herbicides slowly move through and kill the entire weed, whereas contact herbicides rapidly burn down the portion of the weed that came in direct contact with the chemical.
Post-emergent herbicides are available in liquid and granular formulations. Generally, sprayable formulations are absorbed more rapidly through leaves and work faster. By contrast, most granular post-emergent formulations are absorbed through plants’ roots, resulting in slower signs of control on the target weed. Post-emergent herbicides are most effective on younger weeds, but some can control the target weed at any stage. Most commonly used post-emergent herbicides for the landscape are formulated for spray application.
After dead weeds are removed from the bedding area following a postemergent application, LCOs can apply a pre-emergent herbicide and/or mulch for residual control.
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