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Watch for Weeds in Imported Hay

August 20, 2012

Source: South Dakota State University Extension

Shortages in pasture availability have forced many to purchase hay this year, sometimes from other states or lower quality hay. When doing this, it is important to be aware of potential unintended consequences, such as introductions of new noxious/invasive weeds, potentially toxic weeds in the hay, and hay containing herbicide residues that could injure broadleaf crops in future years, says Mike Moechnig, SDSU Extension Weeds Specialist and Roger Gates, SDSU Rangeland Extension Specialist.

"It is illegal to transport hay containing noxious weed seeds in South Dakota regardless if the hay is from this or another state," Moechnig said. "In fact, this is a Class 2 misdemeanor that could be punishable by 30 days in prison and/or a $500 fine."

Gates adds that 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," Gates said.

The specialists say 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," Moechnig said. "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."

Moechnig says 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," Moechnig said. "Lethal doses for some livestock species may be only 0.2 - 0.8 percent of their body weight."

He adds that poison hemlock populations seemed to expand over the past couple years, particularly in northeastern South Dakota, 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," Moechnig said. "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, lambsquarters, pigweeds, thistles, and others can also increase hay nitrate concentrations if present in large quantities."
In addition to unknown weed seeds and plants in the hay, Gates says unknown herbicide residues could also cause problems.

"Grass 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," Gates said.

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