By Scout Nelson
Weed management is crucial in all crops, but sunflowers face unique challenges. There are fewer herbicide options available for sunflowers, especially for postemergence weed control. Some herbicides, like clethodim (Select Max), can be applied after the crop has emerged to control grass weeds.
Additionally, herbicide traits such as imazamox (Beyond Extra) in Clearfield sunflowers and tibenuron (Express) in Express sunflowers help manage broadleaf and some grass weeds. However, kochia and waterhemp in South Dakota have developed resistance to these herbicides.
To manage tough weeds like kochia and waterhemp, preemergence herbicides are essential. Several herbicides from groups 3, 14, and 15 are effective against these weeds. However, their soil residual activity may not last the entire growing season.
For continued weed control, applying another preemergence herbicide after the sunflowers have emerged but before the weeds germinate, known as post residual, may be necessary. This ensures minimal weed competition throughout the growing season.
Pyroxasulfone (Zidua), a group 15 herbicide, can be applied safely between the v1 and v8 growth stages. It must be applied before weed emergence as it does not affect weeds that have already sprouted. Pyroxasulfone is effective against small-seeded broadleaf and grass weeds, including kochia and waterhemp.
The herbicide should be applied when rainfall is expected, as it needs at least 0.5 inches of water to activate. When using this herbicide post residual, different preemergence herbicides should be used to reduce selection pressure on resistant weeds.
Categories: South Dakota, Crops, General, Rural Lifestyle