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Sponsored: Is a Fall-Applied Herbicide for You?
There are several winter annual weeds that emerge in fields every fall that can cost you money and time in the spring. Arguably, the most troublesome is marestail. Although it has the ability to germinate throughout much of the year, it’s the ones that germinate in the fall that are some of the hardest to kill.
Unfortunately, herbicide effectiveness greatly depends on the growth stage of the weed. Once they reach the “bolt” stage (greater than 4 to 6 in.) they become much more difficult to control. The best option is to control marestail in the fall when it’s still in the rosette stage. There are several options to do this, but typically we recommend pairing a product with post-emergence activity like 2,4-D, dicamba, or Sharpen® with a product that will give you residual control like metribuzin, Valor® or Dual Magnum®. Another option would be to use a pre-mix product, like Autumn™ Super, that has burndown and residual activity.
Fall applications can be made immediately after harvest and up through December, as long as the weeds are still actively growing. While these applications can help suppress fall-germinated marestail, they will not provide season-long control and a spring application will most likely be warranted. Figures 1 and 2 below represent what a fall herbicide application looks like in the spring. The lack of weed pressure will help the soil to warm up quicker, allowing for earlier planting.
Figure 1: 48 oz. Gramoxone
Figure 2: 48 oz. Gramoxone + 5 oz. Metribuzin
Fields with a history of Palmer amaranth and waterhemp should also be considered when fall-applying herbicides. Similar to soybeans, these weeds are photoperiod dependent and will reach their reproductive stages quicker as the nights get longer. Figures 3 and 4 were taken from a cornfield that was harvested in September. As you can see from these photos, the Palmer is only 6 to 8 in. tall, but has already established a substantial seed head. Weeds this size are hard to see from the road, but can add a considerable amount of viable seeds to the soil seed bank. A combination of an 8 oz. application of dicamba and 2.5 oz. of Valor, or 48 oz. Gramoxone and 5 oz. metribuzin, will go a long way in controlling these weeds and will save you from headaches in the years to come.
Figure 3: Palmer Amaranth Seed Head
Figure 4: Palmer Amaranth in Reproductive Stage
Please contact your local Beck’s representative if you have any questions about what herbicide program is right for your operation.
Austin Scott | Field Agronomist and Herbicide Specialist