NDSU Extension - Mercer County


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Fall Weed Management

Fall, Weed Management, weeds,

Submitted by Craig Askim, Extension Agent/Agriculture and Natural Resources

Fall is a great time of year to spray for weeds and in most cases the success rates are usually better than chemicals applied in the spring. Most weeds in the spring of the year are harder to kill than in the fall because the weeds during fall months are not actively growing as well as in the spring. Fall is an excellent time to go after weeds such as dandelions, any type of thistles, kochia, foxtails and wormwood in fields and residential settings. This time of year, will also reduce the amount of damage that could possibly occur to desirable trees, scrubs, or garden produce because of a chemical application.

The ideal temperature to apply chemicals on most labels is between 55 to 75 degrees, which makes September and October ideal months to apply chemicals. However, an applicator must understand that not all types of chemicals can be applied during the fall and must pay attention to herbicide carryover rates and mode of actions.

Read and follow all chemical labels before making any chemical applications. Below is a remark from an NDSU Agronomist on how to develop a sound chemical management program for your farming operation. The same type of program could also be used in a residential setting.

Fall is when many growers are beginning preparation for fall row crop harvest. Remember to take weed species and density notes and, if possible, maps spatially representing where you observed tough weeds in fields in 2019. Collect this data ahead of harvest if possible since the combine will eliminate most of the evidence of 2019 weeds.

This data compliments pesticide application records and are critical as growers continue to develop their management strategy for each field in the farming operation. Use your field scouting notes, maps, and your 2020 cropping plans to develop a comprehensive weed management strategy after carefully considering the ‘biology’ of the ‘tough weeds’ challenging your fields.

Continue to learn germination and emergence habits of weeds and timeline when each weed species begins to germinate and its emergence in fields. Above all, study the various herbicide options in-crop, considering mode of action, application timing, and mixtures to augment control and learn of any potential herbicide rotational restrictions for future crops planted in the cropping sequence.

Unexpected weather will always provide a wrinkle to the weed management strategy so develop a backup plan if your strategy needs to be adjusted due to unforeseen circumstances. Finally, do not be afraid to re-evaluate the strategy and make changes to the weed management strategy based on mistakes or disappointing results. Remember that Einstein was the one who stated that “Anyone who has never made a mistake has never tried anything new.”

Source: Tom Peters, Extension Sugarbeet Agronomist, NDSU & U of MN

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