I live beside the Little Campbell River in S. Langley, B.C. and one of my horses has had a bad case of hives for two weeks. Seems to be seasonal, because he's had it before at the same time of year but never this bad. I'm looking for possible causes, and wondering what this plant is and whether its something he could be allergic to. There are masses of these growing in or along the river beside the pasture - some over 10 ft. tall. I'm sure it must be a common wild flower or shrub, but I can't seem to find out the name so I can find out more about it.
