There is error while submitting your request. We use cookies to help personalize content, tailor and measure ads, and provide a safer experience. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Advancing the science of gardening and other stuff since 2009. In Canada, the major impact of Cirsium arvense is in agricultural land, and in natural areas that have been disturbed or are undergoing restoration (White et al. Canada thistle invades natural communities primarily through vegetative expansion, and secondarily through seedling establishment. •What to do: Not “toxic” but can cause irritations in the mouth of animals check animals mouths frequently. If the political process is not the way that legal definitions are made, what do you propose as an alternative? Isn’t that the point of these lists to begin with? Species diversity in an “undisturbed” Colorado grassland was inversely proportional to the relative frequency of Canada thistle (Stachion and Zimdahl 1980). Virginia is a prime example in that there are only two weeds listed yet neighboring North Carolina, with very similar climate and growing conditions, lists over a hundred. (Of course, the goldfinches would disagree with me!). They’re not so much of a problem when the leaves are fresh, but dried/wilted red maple leaves are very toxic to horses, damaging red blood cells and even causing death if enough of them are ingested. Horses are considered the least susceptible animals to nitrate poisoning. Several plants, including nightshade, become more toxic as they wilt and die, posing a danger to horses eating dried hay or plant matter blown into their pastures. Most Canada thistle patches spread at a rate of 3-6 feet/year, crowding out more desirable species and creating thistle monocultures. Once it’s here efforts to stop them aren’t usually that effective (sometimes biological controls will work). Purple thistles are not dangerous at all, any horse i have known acts like the purple thistle is a treat, and they absolutely love them. She is WSU’s Extension Urban Horticulturist and an Associate Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. This highly invasive thistle prevents the coexistence of other plant species through shading, competition for soil resources and possibly through the release of chemical toxins poisonous to other plants. These tips should give you a starting point, but every region has its own list of concerns, and some plants can be hard to identify. Spreading both by seed and rhizome, Canada thistle can create monocultures covering large areas. “PROBLEM: The extensive root system of Canada thistle allows it to out-compete and displace many native species, especially in degraded prairies where native species are not well established. It is toxic to horses after 60-200% of the horse’s body-weight is consumed over an extended period. We (the people of this country) only have so much in the way of resources to combat invasive plants and noxious weeds, so we need to do our best to focus our efforts where it really matters. It grows in circular patches, spreading vegetatively through roots which can spread 10 -12′ in one season. From Montana: Thistles reduce the use of an area for grazing or recreational purposes because of the prominent spines on leaves, stalks, and blooms. PLANTS THAT ARE TOXIC TO HORSES AND LIVESTOCK The following is a guide of several plants that can be found growing in Lincoln County that are poisonous to horses and livestock. Many of these references simply state what noxious is supposed to mean and provide no evidence that Canadian thistle actually fits the definition — that’s not helpful and doesn’t prove anything. The estimated nitrate lethal dose is 61 grams to 152 grams per animal. If Dr. Chalker-Scott can use noxious weed lists as a standard against which to judge permaculture practices, on what basis should folks like me be more or less cavalier about them? Barnaby's thistle A post shared by Baji (@wookeyranch) on Aug 5, 2016 at 10:28pm PDT Both plants appear throughout the Western United States, approximately from Missouri to California, and from Mexico northward, almost to Canada. 2nd cite Colorado: So what is the objective, neutral, criteria that qualifies one weed as noxious, and another not? In Montana, it is estimated that two shoots per square yard can reduce wheat yield by 15 percent and 25 shoots per square yard can reduce wheat yield by 60 percent. Prevention is the best medicine. Varieties of thistle are similarly annoying, with sometimes fierce prickles growing all along the plant. We need a comparison to rate the relative harm of CT. The wind-dispersed seeds may remain viable for 20 years or more, allowing it to spread quickly and making it difficult to eradicate.”. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. It is known to harbor other pest species, e.g., insects, and has long been recognized as an agricultural est. Daniel Johnson is a freelance writer and professional photographer, and watcher of horse movies. because of their invasive nature.”. Both natural and human caused disturbances can create the opportunity for Canada thistle to become established in natural communities.”, Ohio: Bull thistle is much larger; stands 4-5 feet tall. Obviously the selection process varies widely from state to state. The burdock’s very effective method of seed dispersal ensures that the plant can spread quickly. One reference points out that Canadian thistle is toxic to horses — that’s wrong. This may be partially due to the extensive taproot in many broadleaf weeds that allow them to remain green longer into the dry season, thereby appearing potentially attractive to horses grazing in poor pastures. Write CSS OR LESS and hit save. "The Garden Professors" Facebook page - Another toxic plant for horses is Milkweed. Some plants can be quite toxic to horses, so it’s important to watch out for them in pastures and hay.