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Extension by Mealor and Peterson

by Wyoming Livestock Roundup

Minimizing Impacts of Weeds in Your Hay
By Brian Mealor, UW Extension Weed Specialist, and Adrianne Peterson, Sublette County Weed and Pest Supervisor

    Growing, harvesting, transporting and feeding hay for supplemental livestock feed is a crucial component of many ranching operations in Wyoming. Producers without the capacity to raise and store hay often purchase it from other sources, and many recreational horse owners feed hay to supplement a limited grazing resource or when they are packing into remote areas far from their home base. Irrespective of the situation, hay producers and consumers can consider several steps to ensure high-quality hay while minimizing negative impacts from problematic weeds.
    One of the unique properties of hay is that it is very mobile – thanks to human transportation. While a mobile feed resource provides great flexibility when moving feed to where it is needed in a timely fashion, it also has a potential negative side. If weeds produce a seed crop within a hay field, those very seeds can be baled and transported to new areas faster and farther on a vehicle than they would be able to spread by way of natural dispersal mechanisms. These human-mediated dispersal events can introduce weed seed into previously weed-free areas, leading to further weed problems across the landscape. This transport can occur within a ranch or over long distances to other producers’ ranches if hay is sold as part of a hay enterprise.  
    As a hay producer, managing weeds during the growing season can limit the amount of competition for light, soil and water resources that the hay crop will experience. Competitive weeds like Russian knapweed, leafy spurge and Canada thistle can quickly establish and spread in irrigated or dryland hay fields if an active weed management program is not undertaken. Early action – when weed populations cover only small proportions of a hay field – leads to a higher probability of successfully removing the weed from the field. Larger-scale weed problems may require longer-term control strategies or re-planting the field if the situation is extreme. There are many different herbicides available for controlling weeds in hay fields (see
    Always correctly identify the target weed, select a herbicide that will not harm the hay crop and follow label instructions when applying the herbicide. Spot-spraying (spraying only areas where weeds are growing) rather than broadcast spraying the entire field may limit potential negative effects on forage species.
    Limiting the amount of weeds within your hay fields can provide a higher quality (and sometimes quantity) of usable forage for livestock, but there may be another benefit as well. Hay can be certified as weed-free if no live reproductive portions of noxious weeds are contained within the hay at the time of harvest and baling. Certified weed-free hay can bring a premium price for those selling hay, and any hay being transported onto U.S. Forest Service lands must be certified as weed-free. Weed-free forage certifications can be arranged by contacting your local Weed and Pest control district.
    As a consumer (actually a purchaser, since your livestock is the real consumer) of hay, purchasing certified hay provides a level of confidence that you are not introducing potentially problematic weeds onto your property. We must address a few caveats to that statement. Just because hay is not certified does not mean it is always brimming full of weeds waiting to take over your pasture. As is the case with many purchases, an educated consumer is capable of making good decisions, and purchasing hay is no exception. Once you buy a load of hay with a high proportion of unpalatable weeds within, you are likely to avoid purchasing hay from that field again. In comparison, certified weed-free hay does not indicate that the hay you purchase will be completely free of any weed species. Certification provides insurance that there is a very low probability of viable weed seeds or plant parts that can establish new populations will be in the bales. This certification of hay as weed-free serves to reduce the long-distance dispersal of weeds within hay that we discussed previously, not to certify that the hay crop is ultra-high quality forage.
    Harvesting or purchasing hay can be an expensive investment. Taking steps to minimize potential weed-related risks when making or purchasing hay can make the entire process more positive from an economic and ecological perspective. For more information on certified weed-free forage in Wyoming, visit or contact your local Weed and Pest or UW Extension office.
    Brian A. Mealor is an Assistant Professor and Weed Extension Specialist at the University of Wyoming and can be reached at Adrianne Peterson is the Sublette County Weed and Pest Supervisor and can be reached at

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