Oats in Iowa suffer from two major diseases, crown rust and barley yellow dwarf virus. Crown rust appears as orange leaf pustules and also causes yellowing and death of the leaves. Severely affected plants are stunted and produce little grain. The disease usually first appears in late May and can remain active throughout the rest of the season. Spores can be windblown long distances, but in Iowa some initial infections are the result of spread from local buckthorn shrubs. Buckthorn is the alternate host of the crown rust fungus Puccinia coronata.