Soybean Rust (Phakopsora pachyrhizi)


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Chlorotic areas on leaves develop into tan or brown or reddish brown lesions. Within the lesions are tiny bumps or uredinia, especially on the undersurface of the leaf. The uredinia produce urediniospores which when released spread the disease by air currents to other soybean plants.

Premature yellowing and defoliation may occur. Symptoms of soybean rust are often confused with bacterial pustule earlier in infection, but use of a hand lens facilitates observation of urediniospores. Symptoms usually occur from middle to late in the growing season, but soybean plants can be infected at any stage of development.

Urediniospore germination and penetration into the leaf require free water, and, as a result, epidemics are most severe during long periods of leaf wetness. Urediniospores are easily disseminated by wind and can move considerable distances. The pathogen is not seedborne, but plant debris can harbor urediniospores.

Fungicides have been found effective for controlling soybean rust in some countries.

This disease has been confirmed in the contiguous 48 states of the USA.


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