Although most organic gardeners have used fish emulsion as an effective fertilizer for crops, recent research suggests that it can also be used as a fungicide to fight diseases as well. Researchers at McGill University in Canada applied fish emulsion to sandy-loam soils at 1% and 2% (by weight) rates. The soils were infected with a common verticillium fungus that attacks a broad range of garden plants. After one day the verticillium fungal spores in the soil were reduced 39% to 74%. After three days the reduction was 87% to 98% and after six days close to 99%. Fish emulsion's mixture of organic acids had an immediate deleterious effect on the disease spores and continued to work for up to a week killing the verticillium fungus. They also found similar results when applying fish emulsion to soils and monitoring damping off (Pythium) fungal disease on cucumbers.
For more information on this research, go to: American Phytopathological Society.