The Relation of Buckthorn to Losses from Crown Rust of Oats

Crown rust is the most destructive disease of oats in Iowa. Losses during the 1930\u27s and early 40\u27s ran high; 30 per cent in 1941. From 1944 to 1948 very little rust occurred, but from 1949 to 1952, loss estimates averaged $45,000,000 per year. The role of buckthorn (Rhammus cathartica L.) as the alternate host of the crown rust pathogen (Puccinia coronata Corda) was discovered by De Bary in 1866. More recent research has shown all species of Rhamnus susceptible to one or more varieties of this leaf rust producing fungus. Occurring in hedges and as escaped bushes in fence rows, R. cathartica constitutes a two-way threat to the oat crop; aeciospores blown from infected buckthorn leaves cause early spring infection of oat fields when weather conditions are favorable; and, new races capable of attacking previously resistant varieties may be formed since hybridization of the fungus occurs each year on the buckthorn leaves