| BEAN DISEASES: BACTERIAL BLIGHTS |
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Halo
Blight, caused by the bacterium Pseudomonas phaseolicola is
characterized by numerous small dead leaf spots with yellow haloes.
At lower temperatures haloes may be up to 1/2 inch in diameter; at
high temperatures haloes may be absent and entire leaves may be killed
as the bacteria move systemically in the plant. Under humid conditions
a cream-colored ooze is produced in pod spots. Halo blight is favored
by cool wet weather. |
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Common
Blight and Fuscous Blight of beans and lima beans are caused
by the bacterium Xanthomonas phaseoli. Disease is characterized by
large dead areas on leaves. Spots begin as small water-soaked or light-green
areas which later dry out and turn brown with a narrow yellow halo.
On susceptible varieties, spots can expand and coalesce to affect
entire leaflets. Similar water-soaked spots on pods coalesce into
irregular blotches. under moist conditions, a yellow ooze is produced
in spots on pods. Common blight is favored by warm wet weather. |
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Brown-Spot
(Syringae) Blight is caused by the bacterium Pseudomonas syringae.
Symptoms, more common on lima beans than on other beans, include small
reddish-brown irregular circular leaf spots, with distinct margins
and a darkening of some veins on the lower surface of the leaf. As
spots enlarge the centers turn gray and drop out. Pod spots are more
elongate than leaf spots. |
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