Mature poison hemlock. Photo by OSU Extension.

Fall control of tough weeds

By Mark Loux, Ohio State University Extension

We have heard a lot about dandelion, wild carrot, poison hemlock, birdsrape mustard, cressleaf groundsel, and annual bluegrass over the past several years. Fall is the best time of the year to control these and a lot of other weeds that cause problems into the following summer, either because they are well established biennials/perennials or they just don’t respond well to herbicides in spring. It’s also worth pointing out that we seem to have shifted to wet springs that mess with all kinds of operations, including herbicide burndown. 

The inability to apply burndown in a relatively timely manner results in large weedy burndown situations, requiring more complex and expensive herbicide treatments, which can still struggle to be effective enough. Fall herbicide application results in an essentially weed-free field until sometime in April when giant ragweed and a few spring-emerging winter annuals start to creep in. And a much easier burndown situation even with weather delays. We have published a number of articles on this subject, which are still valid and linked below. Here couple changes/additions:

• Where cressleaf groundsel is a problem in alfalfa hay, we are suggesting use of Pursuit + 2,4-DB (Butryac) in the fall, and not Pursuit or 2,4-DB alone. Let us know if you have had luck in the fall with single-component treatment. Spring application of either of these herbicides alone or in a mix is likely to highly variable. Birdsrape mustard is controlled well in the fall with 2,4-DB alone, but also probably not in the spring. Control of both of these weeds is much easier in grass hay, due to the abundance of growth regulator options. 

• Quelex is labeled for application in fall prior to corn and soybeans and should be an effective option in this situation, especially where supplies of 2,4-D or other herbicides are limited.

Here are additional resources:

Scout now for cressleaf groundsel and other winter weeds in hayfields and pastures (2021)

Scout now for cressleaf groundsel in hayfields, or pay the price in May (2020) – complete with link to video, fact sheet, and Powerpoint deck.

Life in a time of glyphosate scarcity – fall burndown (2021) – a good overall resource even if glyphosate is cheap and available

Fall-applied herbicides: odds and ends (2020) – with links to winter annual weed ID info

Five things to know about fall herbicide treatments (2015)

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