Oat Crown and Leaf Rust Alert

In oats, crown (leaf) rust is dependent on European buckthorn as the alternate host and the disease is often serious and substantial losses can occur, especially in Central and Eastern Ontario. The pathogen is not seed or soil-borne and European buckthorn is the primary local source of spores while another source of spores is blown in from the southern US. This spring buckthorn infection (spore production- aecia) is high in many parts of the province and is the important spore source therefore oat producers should be on the alert for crown rust.

There are different races of the fungus and like other rusts they change over time which can affect a varieties performance over time. Crown rust is most problematic when the disease develops early and although the weather conditions have not been ideal to date (mild to warm (15-25°C) during the day and mild at nights (10-20°C) with adequate moisture (rains, frequent dews)) things should become more favourable soon. Temperatures above 30°C stop infection.

The most distinctive symptom of the disease is the production of orange pustules (volcanoes called uredinia) on the oat leaves and sheathes. These pustules can produce thousands of orange-yellow coloured spores which can spread to other fields or infect adjacent plants.

Management

1. Use a tolerant variety. Varieties differ in their susceptibility to the disease and since new rust races develop, this can reduce a varieties tolerance levels Refer to the Ontario Performance Trials for Spring Cereal Crops for specific details.
2. Plant as early as possible in the spring which may allow the plants to escape the disease from late season infection.
3. Foliar fungicides are affective against the disease but they must be applied in a timely manner and close to flag leaf emergence in order to protect the flag leaf. For fungicide recommendations, refer to OMAFRA Publication 812, Field Crop Protection Guide.