Fungal and Bacterial leaf spots of soybean; How not to confuse these with soybean rust

James E. Kurle

Informations

• Publié par: Veseb
• Nombre de lectures: 14
• Langue: English

Extrait

          Institute of Ag Professionals  

      Proceedings of the   2004 Crop Pest Management Shortcourse       www.extension.umn.edu/AgProfessionals          Do not reproduce or redistribute without the written consent of author(s).

Foliar diseases of soybean that look like soybean rust.

Jim Kurle

Department of Plant Pathology

University of Minnesota - St. Paul

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Soybean Rust in Minnesota

Unlikely that Rust will Overwinter in MN

Rust will Survive in Gulf Coastal Areas

–Texas, Louisiana, Florida

Spores will Follow the “Puccinia Pathway”

Risk Analysis Indicates Likelihood of Weather Conditions Favorable for Epidemic – 6 to 15 out of 30 Years.

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Soybean Rust Management

Currently – No Resistant Varieties Available

Management – Timely Application of Fungicides

Protectant Fungicides – Applied Before Infection

Eradicant & Curative Fungicides – Provide Control after Infection (Must be applied very early in disease cycle.)

Identification of soybean rust will be critical.

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Soybean Rust Identification

Identification of soybean rust requires training and experience. A number of other foliar diseases are easily confused with soybean rust. This presentation is intended to help you identify those diseases that can be confused with soybean rust. By eliminating instances where “lookalike” diseases occur diagnostic resources can be focused on symptoms that might be those of soybean rust.

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Soybean Rust

Disease Development is favored by:

–Prolonged leaf wetness,

–High humidity (>75-80%).

–Temperatures between 59-86 F,

•Optimum 77 F

–Presence of Spores

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Soybean Rust

Obligate parasite.

Infection begins on lower, older, leaves.

Initially forms chlorotic “spots”.

Leaf may become chlorotic.

Spots become “lesions”.

Lesions develop into “pustules” and increase in size; change from gray to tan or reddish brown.

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Soybean Rust

Pustules may also occur on stems, petioles, and pods.

Pustules break open and reveal tan to reddish brown spores.

Soybean Rust

When scouting for soybean rust, focus on:

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Early planted fields with early maturing varieties.

Low lying or protected fields with prolonged dew periods.

Fields with early canopy closure.

Soybean Rust

For soybean rust detection on the plant:

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Examine lower leaves of the plant.

Use a 10 to 20X hand lens to detect pustules on underside of leaves.

Use a 10 to 20X hand lens to detect spores released from pustules.

Soybean Rust Lesions

http://www.aphis.usda.gov/lpa/issues/sbr/Soybean Rust 22.pdf _ _