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Expanding Post-Emergent Herbicide Applications

By Eric Reasor, Ph.D.

By Eric Reasor, Ph.D.

Southeast Research Scientist

Summer is the busiest time of the year, filled with mowing, irrigation, cultivation, fertilization, and pesticide applications. This causes valuable time to be spent on herbicide applications. Expanding your post-emergent herbicide applications by combining two or more herbicide products, active ingredients, and modes of action can save time and yield better results. However, choosing the appropriate herbicide for the specific situation can be difficult.

Why?

  1. Save time by reducing the number of applications. Using multiple herbicide products or active ingredients can control a broader weed spectrum. Combine broadleaf herbicide with grass and sedge herbicides to widen the range of a single herbicide application.
  2. Better control on tough weeds. Summer is filled with difficult-to-control weeds, and additional herbicides can provide greater control on weeds such as chamberbitter, doveweed, goosegrass, ground ivy, spurge, Virginia buttonweed, wild violet, Kyllinga spp., and nutsedges.
  3. Herbicide resistance management. This issue is rapidly increasing in turfgrass and applying multiple herbicide modes of action is one of the best methods to manage against herbicide resistance.

How?

  1. Pre-mixed products. Selecting products already formulated with multiple herbicide active ingredients and modes of action is the easiest way to expand your herbicide application. However, not all herbicides are or can be pre-mixed into a single formulation.
  2. Tank-mixing multiple products. Selecting different products to mix together yourself can work when certain herbicide active ingredients are not pre-mixed into a single formulation. It is important to follow recommended tank-mixing steps when mixing products of different formulations (e.g., WDGs mixed with liquid formulations). It is also important to read the product safety data sheet (SDS) for any incompatibility issues.

What?

It is important to look outside the synthetic auxin herbicides (Group 4) 2,4-D, dicamba, MCPP, and MCPA when selecting herbicides. These active ingredients are highly effective on a wide range of broadleaf weeds, but they do not adequately control grassy weeds and sedges. Moreover, there are reported herbicide resistant weeds to these active ingredients.

Quinclorac is a synthetic auxin herbicide that controls more than just broadleaf weeds. It can be very effective for crabgrass control if applied at the appropriate timing and with the addition of an adjuvant. Many pre-mixed products include quinclorac for its control spectrum. Q4® Plus Turf Herbicide for Grassy & Broadleaf Weeds combines quinclorac with 2,4-D, dicamba, and sulfentrazone in one product to control many weeds.

ALS-inhibiting herbicides (Group 2) are great partners for synthetic auxin and other herbicides. They can provide broadleaf, grass, and sedge control depending on the specific active ingredient. For example, metsulfuron has mainly broadleaf activity, whereas flazasulfuron and trifloxysulfuron can control grasses and sedges in addition to broadleaf weeds. Katana® Turf Herbicide (flazasulfuron) mixed with herbicides such as SpeedZone® EW Broadleaf Herbicide for Turf has proven to provide longer-term weed control than either herbicide applied alone.

PPO inhibitors (Group 14) are a great herbicide application addition to increase the speed of herbicide activity. For example, active ingredients carfentrazone and sulfentrazone are safe on cool- and warm-season turfgrasses, and have activity on a broad spectrum of broadleaf weeds. Sulfentrazone can also be used for Kyllinga spp. and sedge control. Carfentrazone and sulfentrazone can be tank-mixed with many other herbicides; however, Avenue South Broadleaf Herbicide for Turfgrass, Q4 Plus, PowerZone® Broadleaf Herbicide for Turf, Surge® Broadleaf Herbicide for Turf, SpeedZone EW, SpeedZone Southern EW Broadleaf Herbicide for Turf, and TZone SE Broadleaf Herbicide for Tough Weeds already include either carfentrazone or sulfentrazone for end-user ease.

HPPD inhibitors (Group 27) or “bleachers” are great for most cool-season turfgrasses to control a variety of weeds. Both mesotrione and topramezone herbicides have activity on crabgrass, nimblewill, and many broadleaf weeds, but control of those weeds increases when combined with other herbicides (e.g., 2,4-D and triclopyr). Topramezone is highly effective on goosegrass, but the threat of herbicide resistance is looming. Tank-mixing SpeedZone EW with topramezone is a great resistance management strategy while also increasing goosegrass control. And the bleaching symptomology on weeds is often negated when mixed with certain herbicides.

Choosing pre-mixed products or tank-mixing with certain active ingredients and modes of action are great ways to expand post-emergent herbicide applications. Herbicide efficacy can be maximized by understanding the strengths and weaknesses of specific herbicide active ingredients. This can save time by controlling more weeds for longer periods of time with fewer herbicide applications, all while managing against herbicide resistance.

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