Fall Control of Perennial Weeds

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Fall is the most practical time to treat perennial weeds because it is the time that plants can move the herbicide to the roots where it will do the most good. When considering fall weed control the emphasis should be on what the patch of weeds will look like next spring or summer not the amount of dead stems this fall. In addition, it is important to consider that a fall application will not eradicate a stand of perennial weeds; rather, the fall application will reduce the stand size or the stand vigor the next year. Fall application of glyphosate is the most flexible treatment for most perennial weeds such as artichoke, bermudagrass, Canada thistle, common milkweed, common pokeweed, dock, hemp dogbane, horsenettle and johnsongrass. Banvel at 2 to 4 pints is also labeled for artichoke, bindweeds, dock, hemp dogbane, horsenettle, milkweeds, pokeweed, or Canada thistle. (Planting small grains must be delayed after Banvel application – 20 days per pint of Banvel applied.)

Fall herbicide applications should be made to actively growing plants. Allow plants to recover after harvest before treating them. Allow 10 days after treatment before disturbing the treated plants. Consider the options of spot treating in a standing crop; keeping the combine header as high as possible so the weeds are quicker to recover; or combining around the weed patches and then spraying those patches immediately after harvesting. Weed species differ in their sensitivity to frost; some are easily killed by frost (i.e. horsenettle) others can withstand relatively heavy frosts. Check the weeds prior to application to be sure they are actively growing.

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