Applied Research
By Jeffrey Derr, Ph.D., Weed Scientist, Hampton Roads AREC, Virginia Tech
C
urrently, there are limited options for weed control in landscape ornamentals, especially for plantings of annual bedding plants and perennials. One new chemical that has been introduced recently for the nursery and landscape industries is dimethenamid, sold in a sprayable form as Tower and in a combination granular formulation as FreeHand. FreeHand contains 1% pendimethalin (the active ingredient in Pendulum), as well as 0.75% dimethenamid. I have been evaluating these two herbicides for several years in a range of ornamental species, but I have focused prima-
rily on annual bedding plants and perennials.
How these herbicides work Dimethenamid is in the same herbicide class as metolachlor, an emulsifiable concentrate (EC) formulation sold in the nursery industry as Pennant Magnum. These preemergence herbicides need to be applied prior to weed germination or applied with a postemergence herbicide if emerged weeds are present. As an EC formulation, Tower contains an oil solvent, with the potential for burning of tender new leaves
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if applied under hot, humid conditions. In general, granular products tend to be safer in nursery crops since they limit the potential for leaf uptake. FreeHand, the granular form, therefore has the best fit for use in landscape beds and is the product I will focus on in this article. The two herbicides in Freehand have different modes of action and a different weed-control spectrum, so there are advantages in combining dimethenamid and pendimethalin into a granular product. The use rate for FreeHand is 100 to 200 pounds product per acre, which corresponds to 2.3 to 4.6 pounds per 1,000 square feet.