How to Control Winter Weeds

We all know that weeds during the growing season can have a negative impact on crop yields. 

It is important to remember, though, that winter annuals—such as marestail, henbit, downy brome, field pennycress, annual ryegrass and shepherd’s purse—can also be detrimental to your operation. Winter weeds can:

  • Rob the soil of nutrients and water;

  • Delay soil warm up in the spring; and 

  • Impact the efficiency of planting equipment. 

All of these issues can lead to decreased yield potential in the following year’s crop.

Winter annual seeds germinate from early fall into December. Broadleaf species generally form a rosette to overwinter and will flower and produce seed by late June to complete the life cycle.

Use a fall-applied herbicide to treat winter annuals

Treatment of winter annual weeds in the fall is a reliable way to get acceptable weed control. Fall treatments can often be less expensive and deliver better control than spring-applied herbicides. The concern of off-target drift is also less of an issue in the fall because there are no actively growing crops.

There are many herbicides from which to select for winter annual weed control. For fields you’ll be planting to corn, some options include the following:

On fields planned for soybeans, here are some options for your herbicide toolbox:

Application rates will vary according to soil type, weed density and weed stage of growth, so be sure to consult with an agronomist before spraying this fall.

When choosing a residual herbicide, remember to check for any plantback restrictions that could impact the next year’s crop. If a long residual herbicide is fall-applied, annual spring emerging weeds can sometimes be controlled into mid-May. That could mean a more timely spring planting with reduced competition. 

Herbicide resistance in winter annuals might be an issue in your region. If that’s the case, you might want to consider spray mixes that utilize multiple modes of action for more effective control.

Why don’t more farmers control weeds in the fall?

There seem to be two primary reasons why farmers hold out on fall herbicide applications:

1. Not enough time or labor

Most years, harvest takes every hour and every person available. But when harvest delays occur, there may be sufficient time to apply herbicides. Even hiring a commercial sprayer can be cost effective in some situations.

2. Not enough cash left in the current year’s cropping budget

Remember that the price of the chemistry chosen for next spring will likely be higher when compared to the price of fall-applied herbicides. Also, weed control will most likely be less effective in the spring, due to the size of overwintering weeds.

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