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The best way to prevent and protect your farm from weeds dispersed by harvesting equipment is to implement an effective weed management program. It is important to manage weeds before they become a problem in a field. Effective programs will provide season-long weed control and prevent weeds from producing seed that can be dispersed, including herbicide resistant weed biotypes.
Weather conditions and challenges with weed control during a growing season may leave some fields weedy at harvest. Fall harvest is an important time to evaluate weed management programs. The location of weedy areas should be documented at harvest to help develop a weed management plan for the following season. Scout fields prior to harvest, note the location of problematic weeds, and take steps to minimize the transfer of weed seeds.
Figure 1. Weed escapes scattered throughout a field could be removed or “hand-rogued” prior to harvest before weed seed matures and drops in the field.
At harvest, fields can be clean of weeds or have varying degrees of weed infestation. Scattered weeds in fields could be removed prior to harvest and before they drop mature seed (Figure 1). A planned harvest order of fields can help to avoid the spread of weeds to un-infested fields. It is best to harvest fields that are clean of weeds first, and harvest the weedy fields last. This is especially important if herbicide resistant weeds are suspected and not present elsewhere on the farm. If necessary, combine around heavily infested weedy areas in a field. Leaving large patches of weeds to remain in a field can help to reduce the amount of weed seed spread throughout the rest of the field. Weeds can also interfere with harvest because they often do not dry down with the crop and may clog harvesting equipment, slowing down the harvest operation. In summary, leaving the weediest fields for last helps to make harvesting operations more efficient and can be one of the best practices to minimize the spread of weed seed.
Weed seed can be dispersed within and between fields by all harvesting equipment. Prior to the first harvest, thoroughly clean all equipment including combines, tractors, trucks, wagons, augers, and tarps. Weed seeds can travel on tractor tires as well as on the combine. During harvest, equipment should be cleaned prior to moving to another field to help minimize the spread of weed seed. The most common and efficient methods of cleaning equipment include vacuuming, sweeping, and using compressed air or water.
Cleaning the combine should always occur before moving to the next field during harvest (Figure 2). A limited cleaning procedure will generally take up to 30 minutes to perform in the field. For steps to conduct a limited cleaning, see Recommended Procedures for a Between-field Combine Clean-out.1 This procedure will help to reduce the quantity of weed seed moved from field-to-field by the combine. It will be more effective for removing large weed seeds like burcucumber than it will small weed seeds like Palmer amaranth. A more thorough, top-to-bottom cleaning of the combine can take up to 6 hours to perform and may not always be practical once harvest begins.2 Consider thoroughly cleaning the combine after harvesting fields infested with weeds like Palmer amaranth, on rainy days, and again at the end of the season.
Figure 2. Clean combine especially after harvesting weedy fields.
Sources 1 Anderson, M. and Hartzler, B. 2018. Harvest considerations to reduce weed seed movement. Iowa State University Integrated Crop Management. https://crops.extension.iastate.edu. 2 Staton, M. and Sprague, C. 2017. Reducing spread of herbicide-resistant weed seed during harvest and tillage operations. Michigan State University. http://msue.anr.msu.edu. Web sources verified 09/17/18.