Importance of a Fall-Applied Herbicide​

While harvesting this fall, many growers took the opportunity to take notes regarding any weed pressure that was present in their fields. The notes taken needed to include what weed species are present, the amount of areas affected and the density of the weeds. This information is valuable to help determine a plan to control weed pressure the following year. Now is the time to consider what crop rotation, tillage or herbicide program best fits the situation. Depending upon the production system, geography, time and environmental conditions, there are several reasons to consider fall application of herbicides:

  1. Fields with heavy infestations of winter annuals, biennial and perennial weeds are usually the best candidates for fall applications.
  2. Fall applications of herbicides help spread out the workload, particularly if spring conditions are cold and wet.
  3. Fall applications typically provide better control of tough weeds like marestail than spring applications.
  4. Often, fall conditions are more favorable for control of winter annual weeds than spring because of smaller weed size compared to early spring growth if applications are delayed due to poor field conditions.
  5. Fall applications can provide an opportunity to use additional modes of action for control.

A fall herbicide application should be used to target winter annual, biennial and perennial weeds that have emerged in the late summer and early fall, or are present in the crop at harvest. Some of the weeds that fit this description include chickweed (Figure 1), annual bluegrass, purple deadnettle, marestail (Figure 2), wild carrot, poison hemlock and dandelion.

Figure 1. Mouse-ear chickweed and henbit.

Perennial weeds like horsenettle, smooth groundcherry and woody species like multiflora rose should be treated early while cool-season perennials like Canada thistle, quackgrass and dandelion can be effectively controlled even after several light frosts. These weeds are most troublesome because they overwinter and regrow in the spring, potentially interfering with planting early season crop establishment. A secondary goal for fall weed control management is to prevent seed production in late-emerging summer weeds. Palmer amaranth emerging in late summer or early fall can produce viable seed in as little as 30 days after emergence.

Figure 2. Marestail seedling.

In most cases, burndown herbicides are recommended for fall applications. Occasionally, burndown herbicides are teamed up with residuals to provide additional modes of action that may help control fall weeds plus give some level of control in the early spring. The fall application of residuals does not replace the need for additional residual applications in the spring. Remember to check individual product labels to determine crop planting restrictions when using residual herbicides in case planting intentions change.

To learn more about fall-applied herbicides and get crop- and weed-specific recommendations, visit www.RoundupReadyPLUS.com.​​

 

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