HELPFUL HINTS HELPFUL HINTS
HELPFUL HINTS
FROM THE LAWN INSTITUTE FROM THE LAWN INSTITUTE
FROM THE LAWN INSTITUTE PREEMERGENCE HERBICIDES
(12 to 15 degrees C) for crabgrass and 60 to 65 degrees F (15 to 18 degrees C) for goosegrass.
As the saying goes, the best defense against weeds is dense, healthy grass. Tere is no doubt that a dense ground cover reduces the amount of light available for weed-seed germination, and this is the first and best line of defense. In many cases this will reduce or even eliminate the need for herbicidal weed control. However, when used properly, herbicides are a very effective tool in many turfgrass management programs. Herbicides can have preemergence properties, postemergence properties, or both. As the names suggest, preemergence herbicides are most effective when applied prior to weed emergence and postemergence herbicides are most effective when applied after emergence. While both types of products are valuable, this edition of TLI Helpful Hints focuses on the proper use of preemergence herbicides.
Tere are many different preemergence herbicides on the market that can be used in home lawns. Tey have different trade names, formulations, ingredients, use rates, modes of action, etc., and it is important to understand the impacts of each. Commonly used herbicides in home lawn products often include prodiamine, pendimethalin, dithiopyr, and others. Tese products control annual broadleaf and grassy weeds by preventing cell division, photosynthesis, or other plant processes in newly emerging weed seeds. Tey need to be applied prior to emergence, not germination, and as such don’t prevent the weeds from germinating, but rather prevent them from ‘emerging’ through the turfgrass canopy. Tey can be applied during the fall months prior to the emergence of winter annual weeds and/or during the spring months prior to the emergence of summer annual weeds. For summer annual weeds like crabgrass (Digitaria sp.) or goosegrass (Eleusine indica), preemergence herbicides should be applied when soil temperatures begin to stay above 55 to 60 degrees F
One of the main benefits of preemergence herbicides relative to postemergence herbicides is that they have a long-lasting effect that prevents weeds from emerging for weeks, or even months, without any injury to the desired turfgrass. Tis reduces the need for follow- up postemergence applications which often are more expensive, more selective in the weed species they control, and more injurious to desired grasses. One of the ways to extend the length of preemergence weed control even longer is through the use of follow-up applications. Herbicide labels often recommend specific timing and rates for re-application intervals, and they will sometimes even do so based on the target weed species. Follow-up applications are particularly useful in warmer, southern climates where the growing season for summer annual weeds is simply too long for the residual control provided by one application.
Regardless of which product you choose, preemergence herbicides can only be applied in liquid or granular form. Liquid herbicides can be applied through various types of sprayers (backpack, hose-end, spray-gun, etc.) while granular herbicides are applied through rotary or drop spreaders. One distinction to mention is that granular herbicides are often impregnated on a fertilizer carrier for easier application. Regardless of which product you use, it is important to water the product into the lawn and through the thatch layer, so it reaches the soil. As with any product, be sure to follow the labeled directions for successful use and to maximize the advantages of preemergence herbicides in home lawns.
For more information on lawn care and helpful “How to” tips, visit The Lawn Institute at:
www.TheLawnInstitute.org.
TPI Turf News January/February 2019 9
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