Toxic effects of ammonia on vegetation in Ontario

Ammonia injury to vegetation has been observed frequently in Ontario in recent years due primarily to increased agricultural use of liquid ammonia fertilisers. Of twelve major incidents of ammonia injury to vegetation investigated recently, eleven involved the manufacture, storage or transportation of liquid ammonia fertiliser. One case involved spillage of ammonia from a large refrigeration system. Data on foliar injury symptoms and relative susceptibility to ammonia were compiled for over a hundred species of native and cultivated plants injured in these episodes. Symptoms of acute injury on woody plants usually consisted of large, irregular, dark brown or black necrotic lesions scattered over the surface of the leaf. Some thin-leaved herbaceous plants developed necrotic lesions that bleached to an ivory or light tan colour. The most susceptible species were balsam poplar, red mulberry and catnip. Maples and conifers appeared to be very resistant to foliar injury.