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2020 Summary of Herbicide Evaluations for Marestail (Horseweed) Control in Soybean

February 11, 2021
Marestail infestation in a soybean field at the ISU Research and Demonstration Farm near Ames, IA in 2020.

Marestail is one of the most widespread and troublesome weeds in Iowa croplands. It can grow to a height of 1.5 to 6 feet, produce up to 200,000 seeds, and can reduce soybean yields up to 80% if not controlled (Figure 1). Marestail seeds are light and disperse across landscapes with winds. Seeds have little dormancy and can germinate soon after seed shed. In general, 75% of seedlings germinate in fall, remain in rosette-stage until spring, begin stem elongation in April, and start flowering in July. About 25% of seeds germinate in the spring.

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Fate of weed seeds in the soil

Encyclopedia Article

The fate of weed seeds in the soil has been an area of much research in recent years.  Most studies have focused on the seeds that successfully produce seedlings since these are the seeds that cause immediate problems for farmers.  In most studies, annual emergence typically accounts for 1 to 30% of the weed seed  in the soil.  Thus, the majority of seeds found in the soil seed bank fail to produce seedlings in any given year.

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Clean Combines to Avoid Weed Seed Contamination Across Fields

September 27, 2016
Weed Seed Trail from combine image

Removing biomaterial to avoid moving weed seeds between fields can be a daunting task. Typically, combines hold 125-150 lbs of grain and biomaterial after the unloading auger has operated “empty” for one minute. A true clean-out requires about six hours to remove as much biomaterial as possible. While a thorough, top-to-bottom cleaning of the combine is best to avoid the spread of weed seeds between fields, spending 15 to 30 minutes cleaning the combine before moving it out of the field will still remove some biomaterial.

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