| Soybean Rust |
Diagnostic Characters for Soybean Rust Identification
Other soybean diseases that have similar symptoms
BACTERIAL
PUSTULE AND BACTERIAL BLIGHT
Soybean rust symptoms appear very similar to the symptoms of two
bacterial deseases. Bacterial pustule is caused by Xanthomonas
axonopodis pv. glycines, especially in the early stages.
Bacterial pustule forms small, light colored pustules with yellow
halos around lesions usually on the undersides of leaves. Figures
9 and 10 shows these symptoms, but the spots can also vary from
specks to large, irregular brown areas which develop when lesions
coalesce. Bacterial lesions usually appear angular between veins.
Click on the small image for a larger image.
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Figure 9. Bacterial pustule symptoms on a soybean leaf. Glen Hartman, National Soybean Research Laboratory, Urbana, IL |
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Figure 10. Detail of bacterial pustule symptoms on a soybean leaf. Glen Hartman, National Soybean Research Laboratory, Urbana, IL | |
| The same holds true for symptoms of bacterial blight, caused by Pseudomonas savastanoi pv. glycinea, sometimes known as angular leaf spot, shown in figures 11 and 12. | ||
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Figure 11. Bacterial blight symptoms on a soybean leaf. Glen Hartman, National Soybean Research Laboratory, Urbana, IL |
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Figure 12. Detail of bacterial blight symptoms on a soybean
leaf. Glen
Hartman, National Soybean Research Laboratory, Urbana, IL | |
The two bacterial diseases can be distinguished from soybean rust by looking at the pustules under magnification, using a hand lens or dissecting microscope. Look for the soybean rust mature pustule with a pore at the top of the cone and masses of urediniospores both within the uredinia and possibly on top of the cone, and usually no yellow halo around the lesion. However, both soybean bacterial diseases symptoms under magnification appear as a yellow halo surrounding a pustule that may be open on the top of the by means of a fissure rather than a pore, and spores are visable within or on top. Under a compound mircroscope, a sectioned bacterial pustule will show bacterial streaming from the inside of the pustule. SEPTORIA BROWN SPOT Another disease seen on the lower leaves of soybean plants that can be confused with soybean rust symptoms is brown spot caused by Septoria gycines of which good images can be found at the Purdue University Plant Diagnostic Laboratory's website. |
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