Bacterial pustule of soybean
Bacterial pustule is caused by Xanthomonas axonopodis pv. glycines. This disease occurs mid- to late season when temperatures are warmer. Lesions are found on outer leaves in the mid- to upper canopy. Lesions start as small, pale green specks with elevated centers and develop into large, irregularly shaped infected areas. A greenish-yellow halo surrounds each lesion. A pustule may form in the center of some lesions, usually on the lower leaf surface. Bacterial pustule will not cause leaves to tatter like bacterial blight.
Disease development is favored by hot, wet weather.
Avoid extremely susceptible varieties where disease is a potential problem; some varieties are marketed as resistant to bacterial pustule. Crop rotation and tillage reduce survival of the bacteria. Bacterial pustule on soybean leaf. Image: D. Mueller
A pustule may be observed in the center of lesions on the underside of leaves. Image: A. Robertson