Plant Protection
 
Soybean Fungus Management
Soybean Rust

Soybean rust caused by P. pachyrhizi has been a serious disease in Asia for many decades. It appeared in Africa in 1997, and in the Americas in 2001. Before it was first found in the continental USA in late 2004, probably brought in by a hurricane, it was considered such a threat that it was listed as a possible weapon of bioterrorism. Soybean rust cannot overwinter in areas with freezing temperatures, but it can spread by wind rapidly over such large distances, its development can be so explosive, and it can cause such rapid loss of leaves that it is now one of the most feared diseases in the world's soybean-growing areas.

Symptoms:
Symptoms begin on the lower leaves of the plant, usually in the lower plant canopy. Small pustules (gray to tan or brown) surrounded by necrotic areas usually develop first on the underside of leaves on the lower part of the plant. Lesions can also appear on pods and stems. Tiny, raised pustules develop in the lesions, and the pustules break open and release tiny tan to gray spores.

Pathogen Involved:
Two species of rust fungi cause soybean rust. Phakopsora pachyrhizi (aggressive Asian pathogen) and P. meibomiae (mild pathogen). Only P. pachyrhizi causes significant yield losses. Both cause the same symptoms, and they can be distinguished only with specialized laboratory tests. These fungi are obligate pathogens that survive only on green, living host plant tissue, and are readily dispersed long distances by wind.

Time of Occurrence:
Can occur at all stages of soybean development, but is most common in or after the middle of the growing season.

Conditions Favoring Disease:
Extended periods of moderate temperatures (59°F to 85°F), wet weather, leaf wetness, and high humidity (over 75%).

Fugicide Cotrol:
Chlorothalonil, Azoxystrobin, Myclobutanil, Pyraclostrobin, Tebuconazole

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