It is said that a weed is any plant growing someplace you don’t want it.
For the most part this is true — for your average everyday plants like dandelions and runaway spearmint. As you will learn there are weeds and then there are WEEDS.
Certain weeds we call noxious. Meaning they proliferate to the point where they crowd out more beneficial plant species to the detriment of crops, forests, and pasture land. Weeds like knapweed varieties, kochia, rush skeleton weed, Russian thistle, field bindweed, mustard, field horsetail, and mullein are a whole host of silent invaders. The University of Nevada has a publication to assist land managers in using livestock to help control noxious weeds. It can be found at: http://bit.ly/Xx4k6I.
But that’s not all they can do. Some plants can kill. Innocuously springing up, first here, then there; on a stream bank, along the edge of a pasture, cropland, or a yard, they grow quietly, unnoticed — until you come along and find one or more of your livestock dead where they lay.
Plants like the death camas, foxglove, yew, water and poison hemlock, castorbean, common cocklebur, milk vetches, false hellebore, tansy ragwort, chokecherry, larkspur, pigweed, jimsonweed, red maple leaves and oleander.
Still, there are plants whose effects aren’t so dramatic, yet just as deadly. These cause irreversible liver damage, kidney failure, respiratory difficulty, weakness, and then death; plants like brackenfern, field horsetail (scouringrush), yellow star thistle, hounds tongue, hemp dogbane, milkweeds, leafy spurge, lupine, locoweeds, fiddleneck, and nightshade varieties.
For the most part, animals tend to shy away from poisonous plants; however, lack of forage will drive them to eat even the most unpalatable of substances. The plants can also make their way into feed stock. When as little as 8 ounces of Western Hemlock can spell death in 30 minutes, getting to know what is growing on your land or where your feed comes from becomes imperative.
Livestock poisoning by plants is preventable by learning to identify what plant species pose the greatest threat to livestock. Some plants are only poisonous at certain times of the year, certain conditions (such as arrowgrass which becomes toxic when stunted by drought), at particular stages of development (such as larkspur which is most toxic during early growth), and affect only certain animal species. Therefore, it is important to know what is growing in your pastures, what type of poisonous plants are known to grow in your area, how to identify them, and the best stage for eradication measures.
The USDA Ag Research Service Bulletin #415 is a comprehensive guide to poisonous plants of the west. It shows the state where the plant is most likely to be found, poison compound, animals affected, symptoms, treatment, and eradication options, available online at http://1.usa.gov/WLx8u8.
OSU Extension also has excellent resources. http://bit.ly/14gHLrS.
For plant identification assistance contact the conservation district or the Master Gardener’s Plant Clinic. Be sure to bring the whole plant, when flowering is best.