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.
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