As crops mature, we get a good chance to evaluate the success of our weed control program. Weeds that have survived control attempts and are present at fall harvest often have produced viable seed which can turn into next year's weed management challenge and pose a threat to future crop yield.
The most severe weed infestations will be easily spotted from the road and seat of the combine. Individual plants and small weed patches may be hiding under the soybean and corn crop canopy and even small weeds can produce seed. Weed seed dispersal is very specific to weed species, giant ragweed and marestail seed is released from the plant at the end of the weed's life cycle.
Waterhemp, common lambsquarters, giant foxtail, common ragweed, and redroot pigweed all retain most of their seeds at the end of the season. Common lambsquarters produces ~62,000 seeds per plant and waterhemp can produce up to ~250,000 seeds per plant. These troublesome weed seeds must be mechanically separated from the plant to spread.
Although a few seeds will drop at the base of the plant, harvesting equipment, unfortunately, does a great job of spreading the weed seeds throughout the field. This fall, look at the corn head stripper plates and the grain platform sicklebar and you will often see a variety of weed seeds. Many weed seeds will be harvested by the combine and deposited out the back of the machine. These will cause challenges over the next few seasons starting next spring.
However, we are more concerned about the weed seeds that remain in the combine. These seeds will slowly leave the combine as you combine future fields. We can take a few easy steps to reduce the movement of weed seeds and help reduce the chance of having more weeds to manage next year.
Scout fields now to see where weed management practices were successful and note where weed challenges are present. Identify the weed species present and the potential for weed seed spread. Use these notes to plan next year's weed management strategy.
Once harvest begins, cleaning weed seeds, crop residue, and soil off machinery before moving to the next field is critical in reducing weed seed spread. A 30-minute combine cleaning goes a long way in reducing the movement of weed seeds. Based on University of Wisconsin-Madison research, most weed seeds found in a combine are commonly located on the corn head and grain platform, rock trap, and feederhouse. Cleaning these areas with a cordless leaf blower works well to quickly remove most weed seed containing material from these areas.
Combine cleaning is noisy and dusty, so wear proper eye, ear, and respiratory protective gear. Always read and follow safety instructions provided by the harvesting and cleaning equipment manufacturer. In-field combine cleaning for weed seeds is not going to remove all the biomass and grain from the combine. A full combine clean-out necessary to switch from one identity preserve grain to another will take hours to days.
The goal of combine cleaning for weed seed management is to remove the most amount of weed seeds in the least amount of time. Combine cleaning is one small step in an integrated weed seed management strategy that requires year-round planning. Every combine will contain weed seeds, and if these germinate next spring and survive to produce seed, each plant can produce thousands of additional weeds seeds. Beyond combine cleaning, harvesting weedy fields last further reduces the chance of spreading weed seeds.
For more information on combine cleaning for weed seed management from UW-Madison search YouTube for "Combine Cleaning for Weed Seed Management."
Daniel H. Smith is the Nutrient and Pest Management Program Manager for UW-Madison Division of Extension
This article originally appeared on Wisconsin State Farmer: A cleaner combine today means fewer weed problems tomorrow, UW experts say