Precautions to Help Prevent the Spread of Weed Seed During Harvest

Excessive rainfall across much of the Corn Belt during the spring of 2019 not only wreaked havoc on tillage, fertilization and planting operations, but it also negatively impacted many farmers’ planned herbicide programs. In many instances, this resulted in missed or skipped preplant-incorporated or pre-emergence applications of residual herbicides meant to control early season grass and broadleaf weeds.


Weed-ridden field Figure 1. Weedy field.

The wet conditions delayed planting into the postemergence herbicide application window, which forced many farmers to make a tough decision choosing between finishing planting their crops or spraying the weeds in the fields they had already planted. Most farmers chose to keep planting.

A reduction in the number of acres receiving a preplant-incorporated or pre-emergence application of a residual herbicide along with delayed postemergence herbicide applications resulted in weed populations that were difficult to control (Figure 1). For soybeans, particularly those planted in 30-inch row widths or greater, late planting resulted in limited row closure, allowing sunlight to reach the soil surface, which promoted continued germination of weed seed, especially waterhemp. Weed resistance to various herbicide chemistries further complicated weed management in 2019.

The challenges farmers faced managing weeds during the 2019 growing season resulted in many weedier-than-normal fields at harvest. Weeds are prolific seed producers, and the seed that was produced adds to the weed seed bank of the field. Fortunately, there are some precautions that can be taken to help prevent spreading weed seed from one field to another during harvest.

The first step toward preventing the spread of weed seed is to scout fields prior to harvest to determine what, where, and how heavy the weed pressure is in each field. While scouting, make a point to look for any weed species that might have escaped herbicide control measures. In some cases, weeds may be limited to just a few scattered plants within a field or two that can be manually removed before harvest.

Combines are great at spreading weed seed from one place to another. With scouting complete, it might be possible to adjust the harvest order of fields to prevent spreading weed seed from fields infested with a specific weed species to non-infested fields.

With the wet spring weather, there are likely drowned-out spots in fields, which are commonly weedy. Harvesting around those areas rather than through them can limit the amount of weed seed running through the combine and potentially carried to another area of the field or to another field altogether. This is especially important when dealing with resistant weed species and/or invasive weed species that are not present in other fields.

An empty combine can retain more than 150 pounds of plant material, so cleaning the combine between fields is a good practice to prevent the spread of weed seed from one field to another.1 However, since a comprehensive combine cleanout can take as much as five hours to complete, a limited cleanout, which only takes 20-30 minutes, is a more practical approach.1,2

In the future, combines may come equipped with a device capable of damaging weed seed, rendering it nonviable. One such device, the Harrington Seed Destructor, could make managing weed seed at harvest less of a concern.1

For more information regarding managing the spread of weed seed at harvest, please contact your local Channel Seedsman and read the Agronomy Advice article titled “Reducing Weed Seed Spread at Harvest.”

Paul Parcher



1Anderson, M. and Hartzler, R. 2018. Harvest considerations to reduce weed seed movement. Integrated Crop Management. Iowa State University, Ames.

2Staton, M. and Sprague, C. 2017. Reducing spread of herbicide-resistant weed seed during harvest and tillage operations. Michigan State University, East Lansing.

Web site verified 8/12/19.



Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields. 

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