Quick facts
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Weed seeds are most commonly a problem as a contaminant in grains.
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As little as 0.25 percent of a horse’s bodyweight in corn cockle seeds can be toxic.
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0.3 to 0.7 percent of a horse’s bodyweight in eastern black nightshade berries can be toxic and may cause death.
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Cleaning or blowing oats can help prevent toxicity.
In this article we will cover corn cockle seeds, mustard seeds and Eastern black nightshade berries.
Identifying
Weed seeds come in many shapes, colors and textures.
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Corn cockle and mustard seeds are round or oval in shape and dark brown or blackish in color.
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Eastern black nightshade berries are small and round. They turn from green to dark purple or black when ripe.
These weeds seeds appear throughout the U.S..
You can find these weed seeds in cultivated fields, gardens and ditches. Corn cockle and mustard commonly appear with small grain crops, like oat. You may find Eastern black nightshade in soybeans and sometimes hay.
Toxicity
The seeds relative to their plant, contain the highest level of toxic chemical. Seeds are usually a problem when they occur as a contaminant in grain (e.g. oats or soybeans).
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As little as 0.25 percent of a horse’s bodyweight in corn cockle seed can be toxic.
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0.3 to 0.7 percent of a horse’s bodyweight in eastern black nightshade berries can be toxic and may cause death.
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A toxic amount of mustard seed is unknown.
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Reduced appetite
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Increased salivation
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Bloat
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Colic
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Diarrhea
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Sometimes, death
Remove the seed source. Horses will normally need fluid therapy with electrolytes. You may need to consider antidiarrhea treatment.
Control
Weeds seeds are common in “bin run,” unblown or unscreened oats. Blowing or screening oats separates the smaller weed seeds and other foreign matter from the oats. Commercial grain sellers and feed stores commonly blow or clean oats. If you grow your own oats, make sure they are blown or cleaned before feeding or seeding.
Other information
Some weed seeds can live dormant in the soil for 20 years or more years. This causes weed problems in pastures and hay fields. Most seeds grow in the first few years after they fall from the plant. Regardless, weed control efforts should focus on reducing or eliminating weed seed production.
Photos provided by Krishona Martinson, PhD, University of Minnesota Extension and the University of Minnesota Strand Memorial Herbarium.
Reviewed in 2021