Fall Ag Weed Control Tips

October 1, 2009 at 1:00 pm

OSU Extension Weed Specialist, Dr. Mark Loux, put together a great article in the September 21 CORN Newsletter. Below, I have summarized the article:

Fall herbicide treatments can have a range of goals, from control of warm-season perennials prior to crop harvest to control of winter annuals that make for a messy seedbed next spring. Optimum timing can vary based on life cycle, but we can roughly lump the various life cycles into one of two categories:

1) Weeds that must be treated before frost, which pertains to all warm-season perennials, including: johnsongrass, pokeweed, milkweeds and hemp dogbane, and horsenettle. The first frost will cause these weeds to shut down, if they have not already matured and senesced. Herbicides are no longer effective after this occurs.

2) Weeds that should be treated after frost and in some cases even after a hard freeze. Winter annuals, biennials, and cool-season perennials fit into this category, and they are often most effectively controlled when herbicides are applied between mid-October and mid-November. Weeds that fall into this category include: chickweed, purple deadnettle, mustards, cressleaf groundsel, poison hemlock, wild carrot, Canada thistle, quackgrass and dandelion.

In general, mixtures of 2,4-D and glyphosate work well.  One of the most problematic weeds in my area is dandelion.  For dandelion, combinations of 2,4-D and glyphosate are recommended, but combinations of 2,4-D with Basis or Canopy are also among the most effective treatments on dandelion.

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