Selective weed control in Christmas tree plantations

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

With the warm temperatures of summer approaching, weed escapes in Christmas tree plantations become a concern. A number of weeds are not adequately controlled by our preemergence herbicides programs. For example, quackgrass (Elytrigia repens) is a difficult-to-control perennial cool-season grass that often escapes both preemergence and postemergence herbicides. The key to all perennial weed management involves diligent and persistent effort over a number of years to reduce and/or eliminate their numbers in the field. Since quackgrass is a cool-season plant, control programs should include herbicides in both spring and fall. In addition, depending upon how long it has been will determine control strategy. Some control options include glyphosate at 1 to 2 qt/A in the spring and in the fall when conifers are dormant and quackgrass is actively growing.

When preemergence herbicides dissipate in mid-summer, annual grasses such as large crabgrass and foxtails emerge and compete with the trees. A number of products are available including Envoy and Poast, which will provide grass control with emerged grass plants. Consult labels for the exact herbicide rates and weed growth stage limitations.

Perennial vines such as wild grape (Vitis spp.) and Virginia-creeper (Parthenocissus quinquefolia) are often observed climbing and covering the Christmas trees. Selective control options include Garlon at 1.0 to 1.5 qt/A in the late summer (no earlier than August) or early fall (before frost or leaf drop on weeds) will provide good control of these problem weeds. Some areas may not be controlled using this method, spot spraying is recommended the following year to clean up these escapes.

Other weeds occur in patches or spots in the field. For example, common milkweed (Asclepia syriaca) and sumac (Rhus spp.) spread in this manner. If caught early, these weed patches can be spot sprayed with glyphosate or Garlon at 1 to 2% solution. The important thing is to treat when plants are small and avoid overspray on the Christmas trees.

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