According to Mark Loux, Ohio State University professor and Extension specialist, fall herbicide treatments have become a fairly common practice for some no-till producers, who recognize their value for managing certain tough winter weeds and providing a weed-free seedbed in the spring.
Loux wrote in a previous year’s Crop Observation and Recommendation Network (C.O.R.N.) Newsletter that control of winter annual weeds can be accomplished by applying herbicides any time after early October. Key point that Loux makes are provided below per his newsletter copy.
The amount of crop residue on the soil surface has not appeared to affect herbicide activity in our research. However, there may be some benefit to waiting a week or more after harvest, where possible, to allow crop residue to settle. For the most effective dandelion control, delay application until after a frost. We have applied as late as early December for control of winter annual weeds, but we generally recommend application when dandelions are still mostly green, or by mid-November if possible.
Fall herbicide treatments should accomplish two major goals. First, the fall treatment has to control winter annual, biennial, and perennial weeds that emerge in late summer or fall or are already present at the end of the previous crop’s harvest. Weeds in this category include chickweed, annual bluegrass, purple deadnettle, marestail, wild carrot, and dandelion, among others. These weeds overwinter and regrow in the spring, interfering with crop establishment and early-season growth, and they need to be controlled by a fall or early-spring herbicide application.
A secondary goal is to prevent seed production by these weeds, which reduces future weed infestations. While they may not provide complete control, fall herbicide treatments are by far the most effective method for controlling dandelion, poison hemlock, and wild carrot.
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, at least until sometime later in April. [This should be accomplished with $12 or less of herbicide.]
Some considerations for fall treatments:
- Effectiveness of the treatment is important—speed of control is not. The most effective fall treatments will result in weed-free fields the following spring, even if they do not appear to be controlling much later in the fall.
- There is a core group of herbicides that will control emerged weeds when applied in the fall. Combinations of two herbicides are usually more effective than any single herbicide, since every herbicide is weak on at least one or two weeds that are found in fields in the fall. [Multiple mode of action herbicides are the common recommendations in this day and age of resistant weeds.]