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Issue No. 7, Article 7/May 20, 2011

Update on Wheat and Oat Rust Diseases

Stripe rust of wheat. Stripe rust was observed on wheat growing in Champaign County last week. Stripe rust thrives in cool (50-60°F), wet weather. If cool weather persists in Illinois, it is important to scout for the presence of this disease. Considering the current growth stages of wheat by region, wheat fields in central and northern Illinois are at the most risk of being affected by stripe rust. The only in-season control is the use of foliar fungicides. Several are effective against stripe rust, but it is important to read labels to understand how late certain fungicides can be applied. As I noted in issue 3 of the Bulletin, applying products that contain a strobilurin fungicide to late-stage wheat (headed out) may not be desirable. University plant pathologists have developed an efficacy chart for fungicides registered on wheat (Adobe PDF).

Stripe rust pustules on a wheat leaf.

Oat crown rust. Small orange spots on the uppersides of the leaves of buckthorn plants with orange cuplike structures on the undersides of the leaves have been observed in Illinois recently. These orange spots and structures are caused by infection by the oat crown rust fungus. Buckthorn, the alternate host for the fungus, is the site of sexual recombination for it, 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 its alternate host, buckthorn.

On oat, 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 airborne and can also cause new infections in other 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.

The only in-season control option for managing oat crown rust is foliar fungicides, including propiconazole products (e.g., Tilt), mancozeb products (e.g., Dithane), and Stratego (a mixture of propiconazole and trifloxystrobin).--Carl A. Bradley

Carl A. Bradley

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