13 - Epidemiology in North America

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Publisher Summary The severity of the wheat stem rust problem in North America over-shadowed the effects of wheat leaf rust caused by Puccinia recondita in the early part of the 20th century. However, a major regional epidemic in 1938 throughout much of central United States on winter wheat emphasized its importance. Leaf rust primarily affects the leaf blades, whereas stem rust attacks the stem; thus, there is less time for a leaf rust epidemic development during the grain-filling period. Yield losses are usually less from leaf rust than from stem and stripe rust. Oat stem rust, like wheat stem rust, has been the most severe in the north central states and adjacent Canada. Crown rust is the most serious rust disease of oats in North America. Epidemics are common in the southern states, where the disease overwinters, and again on late seeded oats in Minnesota, the eastern Dakotas, and Manitoba. Crown rust is common in Mexico. Stem rust epidemics on barley develop more slowly than on wheat for a number of reasons that vary in importance with year and location.