Weed seed in harvested crops can negatively impact a farm’s potential profits. Sometimes the impact can be immediate like crop yield reduction, the rejection of a grain load due to export market regulations; and at other times, it can set the stage for future problems like herbicide resistance and increased control costs.
- 97% of samples contained viable weed seed
- Combine head samples contained
Some additional tips for cleaning combines and reducing the spread of weeds:
Last fall, to validate our concerns of weed seed movement via combines, some UW-Madison Ag Extension Educators and stakeholders took take the time to clean and collect samples from combines before putting them away for the winter. Samples were from four specific locations: head, feeder house, rock trap, and rotor. In total 31 samples from nine different combines were collected. The seed samples were mixed the samples with field soil and potting mix in our greenhouse and observed what weeds emerged after two weeks.
The timing of weed seed control is also important; weed seed management at crop harvest is critical because at harvest, weeds that have survived other control attempts during the growing season and produced viable seed (also called weed escapes) can be spread from farm to farm if equipment is not properly and thoroughly cleaned. Many species have the potential to be troublesome but waterhemp has proven to be exceptionally challenging in recent years.
Finally, steps should be taken to minimize movement of weed seed between fields on harvest equipment. In the future, new technology like the Harrington Seed Destructor (HSD) will make weed management at harvest simpler, but until then, relying on good clean-out practices is necessary in some situations. Combines can retain more than 150 pounds of biomaterial including crop seed, plant material, and weed seed after it has been run empty. A few short steps to perform a self-cleaning of the combine and about 20-30 minutes of time before moving on to another field can help further reduce movement of new weed problems to another field. Read more about those steps in our between-field combine clean-out document.
Harvest is just around the corner for many Iowa farmers and now is a good time to consider options to reduce movement of weed seed between fields with harvest equipment. While we may not think of it during harvest time, combines are extremely effective at transporting seed from field to field. A few precautions leading up to harvest and during harvest can help manage any escaped problem weeds.
Waterhemp is an example of a potentially herbicide-resistant species that may need to be contained, especially when it is out of control in only a few fields on the farm. Palmer amaranth and burcucumber are examples of two species that may be either new or in few enough fields that it is valuable to prevent them from spreading further. These species are especially difficult to manage and preplanning harvest can help reduce problems in future years.
Harvest equipment can carry significant material, including weed seed, between fields.
Prior to harvest, scout fields for escaped weeds since weeds are easier to see after crops have matured. This is important to identify problem fields or areas for next year. Your notes about weed problems are critical to choosing effective management tactics for next year, so make this a priority prior to harvest. In some situations scattered weeds could be removed from the fields prior to harvest. It is much easier to manage weed issues before they drop mature seed or before that mature seed goes through a combine.
If weeds cannot be rogued prior to harvest, decide whether planned harvest order needs to change to avoid spread of certain species to other, uninfested fields. Another precaution when harvesting fields, especially given all the drowned out spots from this spring’s rains, would be to harvest around those areas in the field. These steps are especially important if fields are suspected to have herbicide resistant weeds that are not present elsewhere on the farm or if the fields have a new or unusual species that should be kept from spreading to other fields.
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