Summary Inoculation experiments have shown that the fungus C. can-tuariensis Salm. and Worm., found in 1922 associated with a leaf-spot of hop plants in a commercial hop garden at Canterbury, is the primary cause of the disease. Under experimental conditions infection could be induced by means of inoculations with mycelium from plate cultures or with conidia from infection spots. Conidia, placed on leaves of hop plants in moist air, infected the leaves directly and typical spots appeared within a few days. Severe infection sometimes caused premature leaf-fall.