"This is kind of a strange year for fall treatments because harvest is so late," says Mark Loux, OSU Extension weed specialist. "Any time we get a later harvest, we have the potential for things to get wet because we don't have good drying weather. So there is some concern that farmers won't be able to get across fields because they'll run out of weather."
Fall applications have become standard practice for many growers because the season presents an ideal application window for control of many species of weeds that are problematic in no-till production.
"We have fields that develop fall weed populations that survive the winter and then present problems in the spring," Loux says. "So if we have annual weeds that emerge from late summer into fall, and some biennial weeds and some perennial species, late fall is an ideal time to control them."
Herbicides are applied in the fall primarily for control of an existing infestation of winter annuals or marestail, volunteer wheat, biennials like wild carrot and poison hemlock, or cool-season perennials such as dandelion, quackgrass, and Canada thistle. He says those are the species that are most effectively treated by herbicides in the fall.
Even so, Loux notes that a blanket application strategy isn't the best strategy at all.
"The big picture on fall applications is that not every field needs one," he says. "The exception there is marestail, where we have some coming up in fall, then doing something in the fall seems to make things easier in the spring."
Given the anticipated lateness of harvest this year, he advised closely watching fields to determine which fields most needed a fall application to control existing infestations.
Because during the period when winter annuals are likely emerging this year, fields could develop fewer or smaller weeds because the soybean canopy was covering the ground much later in the season than normal.
"If you go into a field and you just don't see a lot of weeds, then it may be a field that just doesn't need a fall application," Loux says. "We have a core set of treatments we recommend, and those haven't changed much this year."
The full schedule of recommendations can be found via the Crop Observation and Recommendation Network.
Loux said one of the biggest recommendations is to not overdo fall herbicide applications, regardless of the timing of harvest.
"Fall application isn't the place to spend the bulk of your herbicide dollar," he adds. "There are a number of products that are marketed for fall applications with residual that end up being a waste of money."
He advises budgeting between $4 and $12 per acre for a fall application strategy, and noted the importance of using residual herbicides in spring for control of species like common and giant ragweed and marestail.
"We've had cases where a dealer talked a farmer into spending $15 to $20, and that is a mistake," he says.
If time and energy are an issue following a late harvest, one option is to hire a custom applicator to handle fall herbicide applications.
If field moisture conditions prevent a fall application, he said more aggressive work may be necessary in the spring for problem fields, stressing a good burndown application.
"Field by field, as fields get harvested, and you see a bunch of green, those are candidates for fall application. If you only have a few here or there and you sort of run out of energy, it's not the end of the world."