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Controlling Weeds in Fields Following Small Grains Harvest (08/06/15)

My travels took me to the southern end of the Red River Valley on Tuesday, May 4. I was impressed with the great number of combines in fields harvesting wheat and barley.

Controlling Weeds in Fields Following Small Grains Harvest

My travels took me to the southern end of the Red River Valley on Tuesday, May 4. I was impressed with the great number of combines in fields harvesting wheat and barley. Freshly thrashed fields have such a clean look, especially from the highway. However, on closer examination, I was impressed by the number of weeds, especially waterhemp, in the stubble.

Controlling weeds post-harvest is a component of the weeds management strategy since we want to establish zero tolerance for weed escapes and new weed seeds entering the seed bank. Like always, begin by scouting fields and observing weed spectrum and size. Some weeds may have been cut by harvest equipment and are stems without sufficient leaf material to intercept sprays following herbicide application. Allowing time for regrowth to occur will ensure better success with their control. Strategies you may consider include:

  • Tillage is an effective means for controlling small weeds. However, first answer the question, are there weeds that may have gone to seed in harvested fields. For example, redroot pigweed that has flowered can produce viable seed in as little as 10 days after flowering. If the answer is ‘yes’ consider waiting with tillage to allow field mice and birds to eat seeds. Seeds are a source for energy for insects, birds and rodents. An internet search indicates predators of weed seeds can reduce total number of seeds on the soil surface by 5% per day or over time, total losses ranging from 20 to 90%. However, tillage after harvest can greatly reduce predation since predators will not dig for seed.
  • Chemical fallow. There are non-selective and residual herbicide options for controlling weeds post-harvest. Suggestions for ‘chemical fallow’ are found on pages 50 and 51 of the 2015 North Dakota Weed Control Guide. Please be aware of differential efficacy and rotational restrictions to 2016 crops from various herbicides. As always, contact a state extension specialist, your county agent, your ag retailer and/or your crop consultant if you have questions.

Tom Peters

 Extension Sugarbeet Agronomist

NDSU & U of MN

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