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Issue No. 9, Article 9/May 25, 2007

Oat Crown Rust Pathogen Is Currently Active on Buckthorn

If you have seen any buckthorn plants in the last two weeks, you may have noticed small orange spots on the upper side of the leaves and orange cuplike structures on the underside. These orange spots and structures are caused by infection of the oat crown rust fungus, Puccinia coronata var. avenae. The buckthorn plant is the alternate host for the oat crown rust fungus and is the site of sexual recombination for the fungus, giving possible rise to new races of oat crown rust. Spores produced on the buckthorn leaves, known as aeciospores, are carried by wind to oat fields, where they can cause infection on susceptible oat varieties.

Oat crown rust on the alternate host, buckthorn.

On oats, the symptoms of oat crown rust appear as orange-colored pustules on the leaves. Pustules may also appear on leaf sheaths, stems, and panicles. After the initial infection by aeciospores, new spores, known as urediospores, develop from those infections and cause additional infections in the field. These urediospores are also airborne and can cause new infections in additional fields. Favorable conditions for oat crown rust include high humidity, conditions that promote leaf wetness (fog, heavy dew, rain), and a temperature above 70°F.

Oat crown rust pustules on an oat leaf (Photo courtesy of G. Munkvold, Iowa State University)

Some of the best control tactics begin early in the year. Choose a variety that has good resistance to oat crown rust. Planting oats as early as possible in the spring may help the crop escape rust infection. Removal of nearby buckthorn plants will reduce the risk of early infection on oat plants. Some fungicides are available that can control oat crown rust, including propiconazole products (e.g. Tilt), mancozeb products (e.g. Dithane), and Stratego (mixture of propiconazole and trifloxystrobin).--Carl A. Bradley

Carl A. Bradley

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