Don’t Spread Weed Seed at Harvest

News Column

John Wilson

Extension Educator

October 4, 2018


Don’t Spread Weed Seed at Harvest

Now that fall is here and crops are mature, it’s easy to see weed escapes that might not have been as visible last summer. Some precautions at harvest can reduce weed seed being moved from one field to another. This will help reduce the weed control challenges next growing season.

An Ounce of Prevention is Greater than 150 Pounds of Unwanted Biomaterial

Combines are one of the largest and most impressive machines on a farm. These large machines effectively remove crops from fields and separate grain from other material to be spread back in the field. Following harvest of an individual field, combines retain significant plant material.

As much as 150 pounds of biomaterial is retained, including chaff, grain, and weed seed. This material may remain in tight spaces within the machine or in obvious places, such as the gathering head and grain tank. While it is impossible to remove all material from a combine, efforts following the harvest of fields can be valuable in reducing movement of weed seed and other material from one field to another.

Most farmers can point to fields with specific problems that other fields do not have, such as marestail, Palmer amaranth, or other difficult-to-manage weeds including herbicide-resistant weeds. Sanitation and appropriate combine clean-out when harvesting these fields should be a top priority to prevent spreading the problem to other fields.

Priorities to Prevent Spreading Weed Seed

To reduce the movement of weed seed from one field to another, farmers should take care to do three steps, whenever possible:

  1. Remove problem weeds prior to harvest to prevent contamination of the combine,
  2. Consider harvest order to prevent carrying seed of problem weeds to currently clean fields, and
  3. Practice good clean-out procedures prior to moving to clean fields.

Combine Clean-out Essentials

Cleaning out the combine prior to moving from one field to another may not be practical in all cases but is an essential step to limit the potential for weed problems moving from one field to another during harvest. A full clean-out may be impractical due to the time constraints of cleaning the complex interior of a combine. However, farmers should focus on priority areas where significant material may remain and be knocked loose in following fields.

20-30 Minute Cleaning Steps

Whether you operate a red, green, or yellow combine, a brief 20 to 30 minute cleaning will remove much of the material that may easily come loose in other fields. Steps in this cleaning procedure should include:

  1. Run the unloading auger empty for at least one minute.
  2. Open the clean grain and tailings elevator doors, rock trap, and unloading auger sump. (Optional: Remove the header from the combine prior to self-cleaning.)
  3. Start the combine and separator.
  4. Adjust the cleaning shoe fan to full speed for maximum airflow and alternately open and close cleaning shoe sieves electronically, or
  5. Adjust rotor to full speed for maximum air suction and alternately open and close the concaves.
  6. Operate the combine this way for at least two minutes for self-cleaning (Optional: Drive over end rows or rough terrain to dislodge material during operation.)
  7. Clean any material left in the rock trap.
  8. Use a leaf blower or air compressor to remove material from exterior of the combine, focusing on the head, feederhouse, and axle and straw spreader at the rear of the machine.
  9. Remember to close the doors to the rock trap, clean the grain elevator, and the unloading auger sump.


This clean-out procedure will not reduce the importance of practicing weed control tactics like removing weeds prior to harvest or choosing harvest order to prevent cross-contamination of fields. It will reduce movement of material and weed seed to fields harvested later in the season. At the end of the harvest season, a full combine clean-out should be completed for maintenance of the machine.

This information was taken from HARVEST HELPLINE: COMBINE CLEAN-OUT prepared by the North Central Agriculture and Natural Resources Academy. (December 2017).

About katcountryhub
I am a graduate of Northeast Community College with a degree in journalism. I am married to Jeff Gilliland. We have two grown children, Justin and Whitney and four grandchildren, Grayce, Grayhm, Charli and Penelope. I will be covering Lyons, Decatur, Bancroft and Rosalie and am hoping to expand my horizons as time progresses!

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: