By Mark Loux
Recap – some brands of glyphosate will be in short supply for the near future, and we’ve also learned that glufosinate may be subject to this also. A glyphosate shortage will have more impact in spring than in fall really, assuming it persists that long. We covered burndown for no-till wheat last week, but this shortage affects fall herbicide decisions also. Some of our past articles on fall-applied herbicides are still current for the most part, and they present glyphosate and non-glyphosate options.
We suggest keeping the cost of fall applications low, avoiding use of most residual herbicides, starting with at least 0.5 lb ae of 2,4-D, and then adding one of the following herbicides:
- Glyphosate – rates as low as 0.38 lb ae/A can be enough in many fields. Increase rate for perennials and weedy fields.
- Dicamba – base rate of 0.25 lb ai/A. Available as premixes with 2,4-D. Our experience is that cold weather affects dicamba more than some other herbicides. This mixture can be less effective on deadnettle and a few other weeds than the other mixtures here, so fields may not look quite as clean in April.
- Metribuzin or Simazine – weaker on dandelion and other perennials than the others listed here but basically get the job done. Metribuzin can be used before corn or soybeans, simazine only before corn
- Any of a number of short-residual ALS-inhibiting herbicides/premixes containing tribenuron and/or rimsulfuron (Basis, Express, Audit, Panoflex, Nimble etc). Most of these can be used before corn or soybeans.
- Canopy/Cloak and other chlorimuron-containing products. These can be used prior to soybeans only and are really the only herbicides on this list that provide a combination of burndown and decent residual activity into spring. Rates at the low end of the rate range are adequate for this.
What is evident from this list it that glyphosate does not have to be an essential component of fall herbicide treatments, and there are other low-cost options. Grasses, and especially perennial grasses, may require the use of glyphosate. We have been hearing a lot about annual bluegrass, because it has been tough to control in the spring. Fall-applied herbicides are effective on this weed, and glyphosate is not the only option (herbicide ratings here). Alternatives to glyphosate for annual bluegrass include Canopy/Cloak, Autumn Super, and Basis and its generic equivalents. Clethodim can be used for control of grasses in fall, but cold weather and mixing with 2,4-D reduce its effectiveness. Although we have not really used it in the fall much, Gramoxone plus 2,4-D is another option for control of most annuals. Activity would be affected by cold and cloudy weather, and we consider this treatment generally more variable and expensive than those listed above. Gramoxone has activity on bluegrass, although is potential for regrowth if warm weather persists into late fall. Note – this information refers to annual bluegrass, not rough bluegrass, which is a completely different animal and requires decent rates of glyphosate.