Winter annuals can be competitive in winter grains like wheat and barley, but also at planting time in no-till corn and soybeans. In addition to winter annuals, simple perennials like dandelion are also quite common in many no-till fields.
Bill Curran, Penn State University weed specialist, says simple perennials are typically easier to manage than creeping perennials like Canada thistle, since they do not have underground vegetative structures that help spread the plants.
"Fall is the best time to control dandelions, while both fall and early spring are the good times to control winter annuals," Curran says. "In the fall, foliar-applied herbicides can be effective as long as the plants are green and appear healthy."
For best activity, Curran recommends applying herbicides when daytime temperatures are above 50 F and nighttime temperatures are above 40 F for several days during application time. In fallow fields, a combination of glyphosate plus 2,4-D ester is fairly effective for control of most winter annual weeds and dandelion.
Curran says application of 2,4-D alone controls many winter annual weeds, but 2,4-D will not control chickweed and is less effective on dandelion than when used in tank-mixes with other herbicides.
"As we move into late November, foliar herbicide effectiveness decreases and the inclusion of a residual herbicide may be desirable in corn or soybean rotations," Curran says. "If you include a residual herbicide, research over the last 5 or 6 years has shown that any chlorimuron-containing product, such as Canopy EX or DF, is at the top of the list for soybeans, while simazine is one of the better products for corn."
Curran adds that other products that have had some success include Valor for soybeans and Basis for corn. In general, he says 2,4-D should be tank-mixed with any residual product.
In a recent dandelion control study, Curran says university weed specialists compared glyphosate alone vs. glyphosate + Canopy EX. Applications were from Oct. 1 to Nov. 15 about 15 days apart.
"In our evaluations the following May, glyphosate alone ranged from 89% with the Oct. 1 application down to 80% with the Nov. 15 timing," Curran says. "The combination treatment ranged from 97% with the early October treatment down to 91% with the latest timing, which showed the benefits of the residual herbicide."
Curran cautions that depending upon the residual herbicide used, a no-tiller will be locked into either corn or soybeans.