Fall weed control breaks down into two types- controlling tough perennials like Canada thistle and dandelion, and secondly, applying an application across the entire field to control winter annuals and provide a clean seedbed next fall.
Whether you still have time to work on Canada thistles may depend upon how hard of a freeze has occurred in your area. The thistles are much easier to do a good job on when they are actively growing. For what you see above ground, imagine many times more roots underground. Your goal should be to apply a herbicide on actively growing thistle so that the plants absorb the chemical and carry it down into the root system.
If you're interested in more general fall applications, which many people have tried lately, then the rules are somewhat different. Company spokespersons claim these applications can save time in the spring, control winter annuals and improve soil conditions.
One company, Valent, is suggesting applications of Valor EXT or Evoke for late fall through winter. Winter annuals such as purple deadnettle, henbit and chickweed, plus marestail, continue to survive through winter, spokespersons note. The winter annual weeds can harbor pests and pathogens, according to Eric Ott, field market development specialist for Valent.
Another problem with winter weeds is that in spring, they can prevent soils form drying out. However, in southern Indiana, some no-tillers say it's almost a trade-off. While stopping short of endorsing them as a cover crop, some imply that a cover or sinter annuals to prevent soil erosion on steeper slopes is better than no cover at all.
There are many herbicides available for fall applications. Experts encourage growers to examine which residual material will keep fields clean throughout the winter months.
"When selecting a herbicide for fall applications in Indiana, it is critical to look for a product with long residual control as well as broad spectrum weed control," Ott says. "Valor XLT will give soybean growers several weeks, even months of control, which is crucial in starting with a clean field.
(Commercial sources contributed to this article.)