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Dry Edible Bean Rust (07/26/18)

Frequent dews and moderate-warm temperatures provide a favorable environment for dry edible bean rust.

Dry Edible Bean Rust

Frequent dews and moderate-warm temperatures provide a favorable environment for dry edible bean rust. Rust is capable of causing yield loss, especially when it first occurs in the early to middle of the growing season. However, rust can be managed with fungicides and scouting for the disease is encouraged.

Signs and Symptoms. Dry bean rust is usually first found on the lower leaves of bean plants in ‘hot spots’, which are clusters of plants with relatively severe damage (Figure 1). Hot spots are often small (a few feet to several yards in diameter) and can occur anywhere in a field, but they are more common near shelter belts or last year’s   residue. Rust is usually first observed on the upper sides of the leaves and appear as dusty cinnamon-brown pustules that may be surrounded by a small yellow halo (Figure 2). Pustules on the undersides of the leaves may appear more robust and lack the yellow halo (Figure 3).

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Management. Dry edible bean rust can cause significant yield loss when the disease occurs early in the growing season and conditions remain conducive for infection and spread. A hot-spot can turn into a full-blown epidemic in just a couple weeks. The best timing for a fungicide application to manage rust is shortly after it is first found. QoI fungicides [strobilurins: FRAC 11] (Headline, Quadris and generics, Aproach, etc.), DMI fungicides [Triazole: FRAC 3] (Proline, Quash, tebuconazole generics, etc.) and mixtures containing these products (Priaxor, Propulse, etc..) have been the most efficacious in our trials. Fungicides with other modes of action, some of which are more commonly applied for white mold (Endura, T-methyl, etc..), have still reduced disease severity but often not as much as QoI and DMI chemistries. Exceptions have occurred.

 

Sam Markell

Extension Plant Pathologist, Broad-leaf Crops

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