Roger Gates
for Tri-State Livestock News

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August 28, 2012
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Weeds cause problems with purchased hay


Most recent drought reports only confirm what grassland managers in the Tri-State area already know. Vegetation growth was severely limited during the 2012 growing season. The result is feed shortages from pasture and anticipated deficits for winter feed. Many managers will purchase hay this year, sometimes from areas less affected by drought or from less standard sources. Weed control is generally good in fields harvested annually for hay. “Forced harvest” stimulated by drought may result in hay produced from areas, particularly CRP acres released for haying, where weed control has not been good. It is important to be alert to unintended consequences that may accompany importing hay from less familiar areas or sources. These potentially may include: introduction of new noxious/invasive weeds, potentially toxic weeds in the hay, and hay containing herbicide residues that could injure broadleaf crops in future years.

It’s the law

According to Dr. Mike Moechnig, SDSU Extension Weeds Specialist, it is illegal to transport hay containing noxious weed seeds in South Dakota regardless if the hay is from this or another state. In fact, this is a Class 2 misdemeanor that could be punishable by 30 days in prison and/or a $500 fine. However, this law applies to situations in which the violation constitutes a “substantial” risk of contaminating fields or other land. Avoiding known weed patches at harvest will reduce contamination. Hauling bales that are net wrapped or tarping the load will minimize the risk of excessive weed seed distribution.

Weed control is necessary

While transporting hay includes some risk of weed seed dispersal, perhaps the primary motivation to avoid weedy hay is to avoid future weed infestation problems on your property. Fortunately, weed infestations generally do not explode in a single season so watching for noxious or invasive species next year should enable effective control of new infestations before they become a costly problem. Leafy spurge, Canada thistle and yellow toadflax are likely some of the most difficult weeds to control that may be present in grass hay so it is particularly important to be watching for these weed species next year. Pictures of noxious weeds and control recommendations may be found on the SDSU Extension Weeds web site and on iPhone and Android cell phones apps provided by SDSU.

Infestation risk may also be minimized by careful management of hay feeding areas. Drought conditions reduce the vigor of pasture vegetation increasing bare ground and enhancing successful weed germination and establishment in the following growing season. Feeding imported hay in a restricted area or even in corrals may contain the area that needs to be carefully monitored the following spring. Careful spring and summer monitoring of hay feeding areas increases the chances of identifying weed infestation while plants are immature, and more easily controlled.

Toxic weeds

The need to hay areas normally not harvested could also increase the risk of having toxic weeds in the hay. Perhaps the most toxic weeds are poison hemlock and waterhemlock. Lethal doses for some livestock species may be only 0.2-0.8% of their body weight. Poison hemlock populations seemed to expand over the past couple years, particularly in northeastern SD, which may be partially due to greater precipitation rates. Hemlock species are in the carrot plant family, so flower clusters resembling carrot flowers may be visible in hay. Whorled milkweed is another weed of concern, but populations are often not very dense, particularly in areas with taller grass that may be hayed. Common weed species, such as kochia, lambsquarter, pigweed, thistles, and others can also increase hay nitrate concentrations if present in large quantities.

Herbicide residues

In addition to unknown weed seeds and plants in the hay, unknown herbicide residues could also cause problems. Hay harvested from areas treated with herbicides such as picloram (Tordon, Grazon), aminopyralid (Milestone/ForeFront), or clopyralid (Curtail, Stinger) could still contain residues of these herbicides that will quickly pass through livestock and can remain in their manure. Spreading this manure or feeding bales on fields that may be planted to broadleaf crops next year could result in severe crop injury. These residues could persist in the soil for 2-3 years. Therefore, it is important to keep manure in pastures if it is not known exactly what herbicides were applied to the hay field .

Concerns of weeds and herbicide residues do not have to be limiting factors when purchasing hay. Properly responding to risks of new weed infestations or contaminated manure can enable producers to avoid greater and more costly problems in the future.




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Tri-State Livestock News Updated Aug 29, 2012 03:54PM Published Sep 26, 2012 09:01AM Copyright 2012 Tri-State Livestock News. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.