By Christy Sprague, Weed Extension Specialist
Fall herbicide applications in wheat have gained popularity over the last couple of years. However, as with any changes in production practices, there are both potential benefits and drawbacks to fall herbicide applications in winter wheat.
Fall-Applied Herbicide Benefits
- Opportunity to control winter annual broadleaf weeds in no-till wheat. Common chickweed, henbit, horseweed (marestail) and other winter annuals can compete with emerging wheat, especially if wheat was no-tilled into soybean stubble without a burndown herbicide. Fall applications of Huskie or Affinity BroadSpec will provide good-to- excellent control of many of these winter annual weeds. Note: Affinity BroadSpec will not control Group 2- (ALS) resistant horseweed (marestail).
- Opportunity to control common windgrass. Common windgrass is a winter annual grass that has become more problematic. Fall applications of PowerFlex HL or Osprey can effectively manage windgrass. Both of these herbicides can also provide good control from spring applications. Applying these herbicides in the fall provides the greatest opportunity to reduce windgrass competition.
- Opportunity to frost-seed clover. One of the challenges with frost-seeding clover in wheat is all herbicides applied in the spring, with the exception of MCPA, will kill or greatly reduce clover stands. From our research frost-seeded clover has been able to tolerate fall applications of Huskie, Affinity BroadSpec, Clarity, Osprey and PowerFlex HL. Note: On occasion, there has been some slight clover stand reductions from fall-applied Osprey and PowerFlex. Fall-applied Huskie may cause some initial clover bleaching.
Fall-Applied Herbicide Drawbacks
- Limited window for application. The application window for post-emergence fall herbicides can be fairly narrow. This window is limited by the minimum wheat growth stage for each product (i.e., 1- to 3-leaf) and the weather. Fall herbicide applications can usually be made through mid-November. However, the general rule of thumb is to apply during periods were daily temperatures exceed 50 F.
- Little to no control of spring emerging winter annuals or summer annual weeds. Many of the herbicides we are using in the fall do not have residual activity to control spring emerging winter annuals (i.e., horseweed) or summer annual weeds, like common lambsquarters and common ragweed. However, good wheat stands can usually outcompete some of these spring emerging weeds.
- Replant crop flexibility. One potential issue to fall herbicide applications in wheat is what crop can be planted if the wheat crop is lost due to winter damage or other circumstances. Replant crop flexibility will be dependent on the herbicide’s rotational crop intervals. Depending on the herbicide, corn or soybean may not be able to be planted if rotation crop intervals are not met.