Mark Loux at OSU recently emphasized these summary points:
- The primary reasons for fall application is for control of an existing infestation of winter annuals or marestail, or control of biennials (wild carrot, poison hemlock) or perennials (dandelion, quackgrass, Canada thistle) that are most susceptible to herbicides in the fall; low populations may be adequately controlled with spring burndown treatments. The primary value of fall herbicide treatments is control of weeds that have emerged by the time of application, which typically results in a weed-free field next spring, or at least until sometime later in April. This can be accomplished with about $4 to $12 worth if herbicide.
- The core group of herbicides that will control emerged weeds when applied in the fall include the following:
· Soybeans Set Up programs for next spring
o Canopy EX or DF + 2,4-D – can be used prior to soybeans. The only one of the treatments listed here that provides residual control into the following spring/early summer. The lower labeled rates of Canopy are adequate for control of emerged winter annual weeds. Canopy DF may not adequately control chickweed unless mixed with glyphosate, metribuzin, or Express. Canopy treatments have been the most effective for control of dandelion.
o Glyphosate + 2,4–D
o Metribuzin + 2,4–D (excluding dandelions)
o Sharpen is also labeled prior to soybean. Must be applied prior to the first killing frost. Mostly a marestail program.
o Numerous Authority Products are also available in this market and listed in the Agronomy Guide
· Corn set up programs for next spring
o Basis + 2,4–D
o Glyphosate + 2,4–D
o Simazine + 2,4-D – can be used prior to corn. It controls winter annuals only. While simazine is a fairly persistent herbicide, it provides little residual control into the spring.
o Numerous other options available in the Agronomy Guide
· Corn or Soybeans next Spring
o Metribuzin + 2,4-D – can be used prior to corn or soybeans. This mixture controls winter annual weeds only. The metribuzin can provide some residual weed control into later fall, but residual control does not persist into the spring.
o Autumn + 2,4-D or glyphosate – can be used prior to corn or soybeans. Controls winter annual weeds and can suppress dandelions, but overall is not as effective as Basis treatments. The 2,4-D or glyphosate carries more of the load for this treatment compared with the others shown here, so higher rates of these herbicides maybe required.
o Express + 2,4-D – can be used prior to corn or soybeans. Controls winter annual weeds and dandelion, but less effective than Basis or Canopy treatments on the latter.
o 2,4-D + dicamba (premixes = Weedmaster, Brash, etc) – can be used prior to corn or soybeans. This combination controls most broadleaf weeds, but is not as effective as glyphosate-based treatments on dandelion or Canada thistle. In OSU research, application of dicamba alone has not typically provided adequate control when applied in November, but the combination of the two herbicides seems to work.
o Basis + 2,4-D – can be used prior to corn, and also prior to soybeans south of I-70 at rates up to 0.5 oz/A. This combination is effective on winter annuals and dandelion, with some activity on biennials.
o Glyphosate + 2,4-D – can be used in the fall prior to any spring crop. It is the most effective of the treatments shown here on grasses, biennials, and perennials. The combination of 0.38 lb ae/A of glyphosate plus 0.5 lb 2,4-D ester is effective for most winter annuals, and rates of both herbicides can be increased for perennials and biennials or large weeds.
Some other herbicides not listed above can also be used, but their utility is no better and not as good on dandelion as those mentioned above. Glyphosate + 2,4–D is the most effective for control of most perennial and biennial weeds, and glyphosate can be added to the other treatments to accomplish this. Combinations of 2,4–D plus Canopy or Basis have been the most consistently effective on dandelion.
- Among all of the herbicides mentioned above, only Canopy products provide substantial residual control of annual weeds that emerge in spring or early summer.
Mark emphasizes that in most soybean fields, it is a big mistake to apply all of the residual herbicide in the fall, with the goal of making only post emergence glyphosate applications the following year. It is possible to do this with Canopy products in fields with low populations and no glyphosate resistance issues, but most fields benefit from use of residual herbicides in the spring, along with some additional burndown herbicide if needed. Most of the marestail/horseweed in Ohio is glyphosate-resistant, and many populations are resistant to ALS inhibitors. This requires much more intense thoughtful management than fields that don't have multiple resistance.