WENATCHEE, Wash. — The Washington Animal Disease Diagnostic Laboratory received more phone calls about a plant toxic to horses in the past year than it has in the previous 12 years combined.

People are probably recognizing Hoary alyssum more and it’s probably spreading, said Patricia Talcott, a Washington State University associate professor and veterinary diagnostic toxicologist at the lab.

She spoke to some 500 people attending the Washington State Weed Association’s 65th annual conference on Nov. 4.

The number of calls, now dozens, may be increasing “because a lot of us in the plant world are talking about it more,” Talcott said.

Hoary alyssum, listed as a noxious weed in some states, can be found in alfalfa and is toxic to cattle and horses but is more of a problem in horses, she said.

At 10 percent of a horse’s feed, it can increase foot temperature, which causes swelling from the knee down in one or more legs and can turn into laminitis, a crippling disease for which there is no specific treatment, Talcott said.

Detection and removal of feed containing Hoary alyssum can lead to recovery but laminitis can also lead to euthanasia, she said.

The specific toxin is not known, she said. The USDA ARS Poisonous Plant Laboratory in Logan, Utah, might study it if it were more widespread and a concern to people, she said.

Talcott also talked about several other weeds and a couple of pesticides harmful to horses and cattle.

Yellow starthistle and Russian knapweed, in large quantities, impair the part of a horse’s brain that controls swallowing and can lead to euthanasia, she said.

Both weeds are common in the West.

“Usually we see it with people who move in from other states. They buy a place and think all the purple and yellow flowers in the pastures are beautiful and put horses out on it and it kills them,” she said.

By far, the most common toxicology problems involve acute nitrate poisoning from pigs weed and lambsquarters, she said. A steady diet of tomato vines can kill pigs and mustard plants and false dandelion are problematic, she said.

Paraquat and 2,4-D are the two most common household and farm pesticides that if spilled or used improperly can be poisonous to dogs and other animals, she said.

Fresh and spent hops are also toxic to dogs, but poinsettias are not to be feared, Talcott said.

“Of 22,000 calls about exposure of poinsettias to cats and dogs, 21,000 had no signs,” she said. “The others had mild vomiting.”

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