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Preemergence Weed Control

Preemergence herbicides are used to control weeds before the weed seeds germinate. If you have not done so already, you should apply these products soon. In certain areas of the state, some weed seeds have already germinated. However, many are still lying dormant and will be controlled by preemergence herbicides.

Applications of preemergence herbicides are useful in many sites—landscape beds containing trees and shrubs, tree rings, perennial plantings, annual flower beds, and in mulched and graveled areas. Be sure the type of site to which you wish to apply the herbicide is listed on the product label. Future planting areas and flower beds should not be treated until—or preferably after—planting.

Remember two things when choosing a preemergence herbicide: First, no single preemergence herbicide will control all germinating weed seeds. Product labels list the weed species the product has been shown to control. Consult previous scouting notes to determine if one weed is particularly problematic, and be sure the product you choose will control it. Second, herbicide labels list the landscape plants that the product can safely be applied over. If a particular plant is not on the list, damage could occur if that plant comes into contact with the herbicide. New plant species are added to most product labels each year, so check them carefully.

Consult the Illinois Commercial Landscape & Turfgrass Pest Management Handbook, 1998–1999 for a complete list of preemergence herbicides and their uses. Products with a broader spectrum of weed control and an extensive list of ornamental plants on their labels include Preen, Pendulum, Ronstar, and Surflan. These products control many broadleaf and grassy weeds. Products labeled to control annual grasses include Barricade and Pennant. If nutsedge is a problem, Pennant controls the germinating seeds.

Finally, most preemergence herbicides do not control existing vegetative structures such as nutsedge tubers, quackgrass rhizomes, and field bindweed rootstocks. Perennial plants that produce these structures are often difficult to control. A systemic, postemergence herbicide (such as Roundup) is generally needed to control these type of structures.

Author: Rhonda Ferree


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