Reducing spread of herbicide-resistant weed seed during harvest and tillage operations

Recommendations for reducing the spread of herbicide-resistant weed seed this fall in Michigan soybeans.

Mike Staton, MSU Extension, and Christy Sprague, MSU Extension, Department of Plant, Soil and Microbial Sciences, originally posted on MSUE News

Herbicide-resistant weeds such as Palmer amaranth, waterhemp and horseweed (marestail) are spreading across Michigan, increasing weed control costs and yield losses in soybeans. Because of this, producers need to take action to prevent or reduce the spread of these weeds. Combines, tractors and tillage equipment have been identified as some of the main culprits in spreading weed seed from field-to-field.

The first step is to scout all of your soybean fields prior to harvest and determine if herbicide-resistant weeds are present. Most marestail in Michigan is considered resistant to glyphosate and many populations are also resistant to the ALS-inhibiting (Group 2) herbicides. Palmer amaranth and waterhemp are commonly resistant to glyphosate and the ALS inhibitors and can be easily distinguished from other pigweed species by their smooth and hairless stems. Additional information on identifying and managing herbicide-resistant weeds is available at Michigan State University Weed Science.

One of the most practical and effective methods of reducing field-to-field spread of weed seed is to harvest fields or areas of fields infested with herbicide-resistant weeds after harvesting all of your clean fields.

When infested fields must be harvested before clean fields, a thorough top-to-bottom and front-to- back cleaning of the combine is recommended. However, this may take 4 to 5 hours, so it is probably not possible when moving from field-to-field. When a thorough cleaning is not possible, Iowa State University Extension agricultural engineer Mark Hanna recommends investing 15 to 30 minutes to remove at least some of the plant material before leaving the field. The steps to this procedure are listed below.

  • Remove the combine head and open the doors at the bottom of the rock trap, clean grain elevator and the unloading auger sump.
  • Clear the area around the combine to avoid injury from flying debris.
  • Allow the combine to “self-clean” by starting it up and running it with the thresher and separator at full speed, the concave clearance and cleaning shoe sieves fully open and the cleaning fan set to the maximum speed. Drive the combine over the end rows or other rough ground to dislodge biomaterial.
  • Shut the combine off and use an air compressor or leaf blower to clean the feederhouse, rock trap and head. Using a two-strap dust mask and eye protection is highly recommended when using an air compressor or leaf blower.
  • Close the doors on the rock trap, elevator and unloading auger sump when finished.

While the procedure outlined above will help reduce the quantity of weed seed moved from field-to-field by the combine, it is not as effective for removing small seeds as a complete top-to-bottom cleanout. Therefore, consider thoroughly cleaning the combine on rainy days and again at the end of the season. Information regarding a complete and thorough combine cleanout is available at “Recommended Procedures for a Complete, Top-to-Bottom and Front-to-Back Combine Cleanout” by Iowa State University and MSU Extension.

Weed seeds also travel on tractor tires and tillage implements, so tilling your weed-infested fields after your clean fields is the best way to prevent spreading weed seeds during tillage operations. When this is not possible, remove as much soil as you can from all tires and the ground-working parts of tillage implements before entering a new field.

The steps you take this fall to reduce the spread of herbicide-resistant weeds will also help prevent the spread of soil-borne pathogens such as sudden death syndrome, white mold and soybean cyst nematodes.

This article was produced by the SMaRT project (Soybean Management and Research Technology). The SMaRT project was developed to help Michigan producers increase soybean yields and farm profitability. The SMaRT project is a partnership between MSU Extension and the Michigan Soybean Checkoff program.


If you or someone you know would like to receive News & Notes by email (see our lastest editions below), send an email to .(JavaScript must be enabled to view this email address) and put News & Notes in the subject line. Our hope is to make our email newsletter easy for you to subscribe to, update, or if you are no longer in need of this information, to unsubscribe. Please let us know what you think about the information and do pass News & Notes along to your friends and neighbors.

Events and Happenings at a Glance

October 17 - November 20, 2017 (Tuesdays) - Beginning Spanish for Dairy Farmers, Clinton County RESA, 9:30 - 11:00 a.m., $150 per person (incl. notebook & instructional materials), pre-registration required (15 students max)
October 31 & December 19, 2017- Commodity Marketing Update for Grains and Dairy, via webinar or MSU Extension Office, 171 Dawson Street, Sandusky, Michigan, 10:00 a.m. - Noon, pre-registration required
December 5 - 7, 2017 - Great Lakes Fruit, Vegetable, Farm Market, and Greenhouse Growers EXPO, DeVos Place Conference Center, 303 Monroe Ave. NW, Grand Rapids, RUP and CEU credits available
December 20, 2017 - 2017 Integrated Crop and Pest Management Update, MSU Pavilion, 4301 Farm Lane, East Lansing, 9 a.m. - 4 p.m., $60 (incl. refreshments, lunch, 2018 MSU Weed Control Guide and other bulletins), CCA credits, MDARD credits, and MAEAP Phase 1 credits pending
February 13, 2018 - Core Manual/RUP Review - Shiawassee County, Caledonia Township Hall, 135 N. State Street, Owosso, Review 9:00 a.m., Test 1:00 p.m.; Cost for review $20 (cost for test separate), 3 RUP credits, register here; Test sign-up MDA 1-800-292-3939 or online at; Call for review material availability 989-224-5241
February 27, 2018 - Core Manual/RUP Review - Clinton County, Smith Hall on the Clinton County Fairgrounds, 800 Sickles St, St. Johns, Review 9:00 a.m., Test 1:00 p.m.; Cost for review $20 (cost for test separate), 3 RUP credits, register here; Test sign-up MDA 1-800-292-3939 or online at; Call for review material availability 989-224-5241
March 19, 2018 - Core Manual RUP Review - Gratiot County, Gratiot-Isabella RESD, 1131 E. Center Street, Ithaca, Review 9:00 a.m., Test 1:00 p.m.; Cost for review $20 (cost for test separate), 3 RUP credits, register here; Test sign-up MDA 1-800-292-3939 or online at; Call for review material availability 989-875-5233
On-Going - Mercury Health Thermometer Exchange, MMDHD Building, 1307 E. Townsend Road, Suite 102, St Johns
On-Going - Medication Disposal Programs, click to see specific dates and locations.  You can also check out this website for additional year-around drop-off locations

Tools, Resources & Links

Return to Clinton County