Oats in Iowa suffer from two major diseases, crown rust and yellow dwarf virus. Crown rust appears as the typical 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 May, and can remain active throughout the rest of the season. Spores can be windblown long distances, but in Iowa most initial infections are believed to be the result of spread from buckthorn shrubs. Buckthorn is the alternate host of the crown rust fungus, Puccinia coronata. Buckthorn is infected early in the spring, then the fungus spreads to oats. Once the disease spreads into an oat field, it can move quickly from plant to plant by the urediniospores, which are the familiar orange spores. Under wet conditions, this disease can reduce yields severely. Yield loss due to rust is affected by planting date. When oats are planted late, they suffer greater damage, because they are smaller when first infected, and the disease has a longer period of time to develop and spread.
Yellow dwarf virus causes extreme stunting and discoloration of the leaves. Leaf blotches that are yellow, orange, or red will develop until entire leaves are involved. Plants along the edges of fields are usually affected first. Severely affected plants produce little or no grain. The virus can infect all cereal grains, corn, and grass weeds. It is not considered an important corn disease in Iowa. This disease is spread by several species of aphids, which are more active under warm conditions in the late spring and summer. Again, late-planted oats are the most severely damaged because they may still be in the seedling stage when infected.
Average planting date for oats in Iowa is April 20. If oats are planted too early in a cold wet soil, they will be affected by seedling blights. However, if the soil is dry enough, earlier planting will help reduce losses to crown rust and barley yellow dwarf. Some oat cultivars also have resistance to these diseases. It is advisable to plant these cultivars in Iowa, because both diseases are potentially severe each year. For rust, some previously resistant cultivars are now susceptible, but there are still some (Hazel, Jerry, Belle, Paul) that are resistant. For barley yellow dwarf, no cultivars are highly resistant, but several have adequate resistance (Hamilton, Webster, Hazel, Horicon, Newdak, Ogle, Prairie, Troy, Classic, IN09201). See the Iowa State University Oat Yield Test results for further information on resistance ratings to both diseases.
This article originally appeared on page 18 of the IC-476 (3) -- March 25, 1996 issue.