Soybean Rust Symptoms

Soybean rust identification

Phakopsora pachyrhizi is considered the Australasian species of soybean rust and P. meibomiae is a new world species. P. pachyrhizi is the species currently causing damage in the Southern Hemisphere. Both have the same types of lesions and urediniospore morphology and thus cannot be distinguished except using molecular techniques.

Soybean rust forms two types of lesions on leaves, tan and reddish brown. The tan lesions (Figures 5 and 6) when mature, consist of small pustules with masses of tan colored urediniospores on the surface.

	Figure 5. Tan lesion of soybean rust on a soybean leaf. Courtesy of Reid Frederick, USDA, ARS, Ft. Detrick, MD
	Figure 6. Close up of tan lesions of soybean rust on a soybean leaf. AVRDC, courtesy of Arnold Tschanz, USDA, APHIS, PPQ, Riverdale, MD
Reddish brown lesions (Figures 7and 8) appear different with reddish brown necrotic areas surrounding the pustules.
	Figure 7. Soybean rust tan lesions with reddish brown lesions in the center. Photo by Joe Hennen, Botanical Research Institute, Ft. Worth, TX
	Figure 8. Close up of reddish-brown lesion. AVRDC, courtesy of Arnold Tschanz, USDA, APHIS, PPQ, Riverdale, MD