Equipment that enters a field with mature herbicide-resistant weeds will easily become a vector for the spread of those weed seeds to other fields. Using proper precautions and thoroughly cleaning equipment after working in weed-infested fields can greatly reduce the spread of weed seeds to the next field.
Combines are a common cause of the introduction of herbicide resistant weeds to new fields. They’re a primary mode of weed seed spread across regions of the US including the Midwest, South, and mid-Atlantic. Things that make them a vector are: they process all plants within a field, including weeds, during a time of the year when remaining mature weeds are producing viable seed; there are many small spaces within a combine where weed seeds might hide; they are time-consuming to clean.
Other pieces such as tillage equipment and tractors have also been found to carry weed seed from field to field if they are used when plants have matured and produced seed.
Because many problematic resistant weed species can produce between 50,000-1 million seeds per plant, even the spread of a few seeds can cause a serious and costly infestation within a couple of seasons.
General Tips for Preventing Weed Seed Spread with Equipment Maintenance:
1) Harvest herbicide-resistant weed-infested fields last.
2) Know whether the combine entering the field has recently been in a field containing herbicide-resistant weeds such as waterhemp or Palmer Amaranth. If so, take the time needed to clean it or consider other available options.
3) When purchasing a used combine, take the necessary time to completely clean the combine before use.
4) Utilize an air compressor to remove the bulk of the weed seeds from the combine.
5) Check the rock trap, as weed seeds and debris may be caught here. Drop the rock trap and blow it out with the air compressor between fields.
6) Open trapdoors to clean the grain auger and tailings processor with an air compressor.
7) On a rainy day, consider a thorough 4-5 hour combine cleaning as a rainy day activity.
8) Since weed seeds can also travel on tillage equipment, clean this equipment after infested fields as well.
Case study: Spread of waterhemp via combine in Southeastern Pennsylvania
In August 2016, Extension associates at Penn State University learned of a heavy infestation of mature waterhemp plants in a soybean field in Southeaster PA. A farmer with land neighboring this field was concerned that the 3-year-old infestation could quickly spread to his land if not controlled this year. First glance at the field revealed that the waterhemp was growing in rows, indicative of seed spread via combine during last year’s harvest. The combine used in that field last year may have spread seed to other fields in the area as well. A drive past another field nearby revealed similar rows of waterhemp. As mature waterhemp plants cannot be effectively controlled with herbicides, this level of infestation would need to be manually removed or burned to prevent the millions of seed from dropping.