Weed management is an important component of crop yield.  Driving around the Wayne County area it is obvious some weeds are more difficult to control compared to others, and some fields have more weed challenges than other fields.  It’s a numbers game with weeds and given the seed production capacity of weeds, the odds over time favor weeds when there is a breakdown in control.  For example, one giant ragweed plant can produce up to 5000 plus seeds per plant.  A single marestail plant can produce 200,000 seeds.  A single large common pigweed plant can produce 100,000 or more seeds. Palmer Amaranth, in the pigweed family, can produce between one-half million up to one million seeds per female plant!  If you don’t have a weed issue on a field, you certainly don’t want to bring one in.

One mechanism for weed seed dispersal and spread of weed populations is through harvest equipment.  There are stories of new weed infestations in fields clearly matching combine movement.  If possible, the cleanest, most weed free fields should be harvested first to avoid the spread of weeds between fields.  This strategy is especially important to prevent the movement of herbicide resistance weeds between fields.  Often field conditions, crop maturity, and equipment scheduling does not allow for an orderly harvest progression from cleanest to most weedy field. In these situations, consider combining the weediest portions of the field last and/or scheduling a combine cleaning before moving to another field.

Mark Hanna, Extension Agricultural Engineer with Iowa State University says that a combine will hold 125 to 150 pounds of grain and other “biomaterial” (including weed seeds) after the unloading auger has operated empty for one minute.  It takes approximately 6 hours to truly and thoroughly remove this amount of material.   Barring some weather event that stops harvest, it is generally impractical to take this kind of time to clean out a combine during harvest.  However, Hanna says that spending 15 to 30 minutes cleaning the combine between fields can remove some of the biomaterial, which will help to reduce and minimize the spread of weed seeds between fields.  In a 2016 Iowa State University online crop news article Hanna recommends the following steps:  “First, allow the combine to do some “self-cleaning” by opening doors at the bottom of the clean grain elevator and unloading auger sump on the clean grain tank. Remove the gathering head if time allows. Then, start up the combine; operating the thresher and separator at full speed. Have the cleaning shoe sieves fully open and the fan adjusted to maximum speed. Make sure no one is within 100 ft. of the area to avoid being hit by flying debris. Use the rest of the time available to clean the outside surfaces of the combine, the gathering head, and inside the rock trap. Head removal allows cleaning of the feederhouse and easier access to the rock trap. Remember to close elevator and sump doors when finished.”