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Continue to Actively Manage Drowned-Out Areas of Fields for Weeds (07/16/20)

I traveled north from Fargo through Cass, Traill, Grand Forks and Walsh counties in North Dakota to inspect a sugarbeet field near Hamliton in Pembina County and returned to Fargo via Kittson, and Marshall counties to take notes in sugarbeet experiments near Crookston, MN in Polk county.

I traveled north from Fargo through Cass, Traill, Grand Forks and Walsh counties in North Dakota to inspect a sugarbeet field near Hamliton in Pembina County and returned to Fargo via Kittson, and Marshall counties to take notes in sugarbeet experiments near Crookston, MN in Polk county. I travelled to Kandiyohi county in central Minnesota the following day to collect additional data. Thirteen hours of driving and 690 miles are plenty of opportunities to look at fields. One noticeable observation was drowned out areas in fields.

The area of the field where the crop has drowned out gives weeds an opportunity to grow without crop competition, and potentially produce a tremendous amount of weed seed. Waterhemp in these spots will cause problems for the next five years if they produce seeds. So, what should you do? Some things to consider are whether you can reach these spots with equipment such as mower or sprayers; what is the crop in the field; and what technique will effectively control or kill the weeds?

Herbicides. Herbicide options are limited to approved herbicides for the crop planted in the field since the crop around the drown-out areas will be harvested. Furthermore, you are limited to labeled herbicide rates and application timings. Likewise, consider crop rotation and crop rotational intervals since the field will be farmed in its entirety the following year.

Mowing. Mowing weeds before weeds produce seed will prevent additions to the weed seedbank. However, equipment limitations, accessibility, and the ability to mow areas on a 10 to 14-day schedule or before viable weed seeds are produced are challenges with this option.

Tillage. Tillage might be a convenient method to manage weeds. However, moving tillage equipment into drown-out areas in a timely manner and throughout the season may not be feasible. Additionally, leaving drowned-out areas void of living plant material could increase concerns with fallow syndrome.

Cover Crops. Planting a cover crop in drowned-out areas may suppress weeds and may prevent fallow syndrome. Species selection, herbicide interactions, and cost are considerations when determining which cover crop is the best fit. Soybean can be planted as a cover crop where soybean was originally planted. This may be the one of the better options if low-cost seed is available, although do not expect any harvestable grain from soybeans planted after mid to late July. Previous herbicide applications may hinder cover crop establishment. As a general guideline, grass cover crops are at greater risk of injury where grass herbicides were applied, and broadleaf cover crops are at greater risk where broadleaf herbicides were applied. Higher cover crop seeding rates may help offset potential stand reductions, although there are no guarantees. Consult the herbicide label for herbicides applied prior to drowned-out areas.

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Tom Peters

 Extension Sugarbeet Agronomist

NDSU & U of MN

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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