G. P. Darnell-Smith and the introduction of copper carbonate ‘dry pickling’ of wheat seed

Abstract

George Percy Darnell-Smith (1868–1942) was the second plant pathologist appointed to the New South Wales Department of Agriculture. Although he founded the Microbiology Branch (later Plant Pathology Branch) and wrote articles on many plant diseases, his noteworthy contribution was developing the ‘dry pickle’ treatment for common bunt of wheat during the 1910s. Darnell-Smith built on the knowledge gained over the previous 150 years on this disease. Common bunt was the first disease—plant, animal or human—whose cause and disease cycle were found. Mathieu Tillet pioneered scientific study of plant disease with his work on bunt in the 1750s. His microscopic examination showed that minute spores infected wheat seedlings leading to bunt developing in place of wheat seeds. His field experiments found that ‘pickling’ seed with copper solutions and other toxic chemicals prevented the disease. Farmers and researchers refined these wet treatments but they remained tedious to use and reduced seed germination and seedling emergence. Darnell-Smith developed an improved treatment with copper carbonate dust that gave effective control of both seed- and soil-borne inoculum. He patented a simple machine for on-farm use. His treatment had advantages over the wet pickles, being much simpler to apply and not affecting seed germination. After confirmation in the United States of America in the early 1920s, the treatment was rapidly adopted there and in other countries where by 1930 it had reduced bunt from a common disease to one rarely seen. Darnell-Smith said that he chose to work with copper carbonate based on studies by F. C. Clark in the United States of America. However, the German scientist Carl von Tubeuf had described its effectiveness as a dry powder against bunt in 1902. Darnell-Smith lectured in England before moving to Australia so it is possible that he knew of this work. Perhaps the considerable anti-German feeling in Australia during World War I dissuaded Darnell-Smith from acknowledging von Tubeuf.