Alan
McNab
Professor of Plant Pathology |
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| Root Rot is caused
by a complex of several different soil-borne fungi. Symptoms vary,
depending on organisms present and on environmental conditions. Root
rot should be suspected whenever plants wilt and die, leaves turn
yellow or drop off, plants are stunted, or pods are small with under-sized
seed. Characteristic symptoms caused by four major root rot fungi
are described here. |
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Fusarium
Dry Root Rot is caused by Fusarium solani f. sp. phaseoli.
Symptoms appear soon after seedling emerge. The taproot is first slightly
discolored, gradually becomes brick red, and finally becomes brown
with longitudinal cracks. Bottom roots usually are killed; new fibrous
roots may form just above the discolored area and just below the soil
surface. Continuous bean cropping allows a buildup of the fungus in
the soil. The fungus can survive for 5 years or longer in the absence
of beans.
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Rhizonctonia
Root Rot, caused by Rhizoctonia solani, is characterized by
seed rot and a water-soaked stem rot near the soil line which in new
seedlings results in wilt and death. More commonly, slightly sunken
reddish-brown longitudinal stem cankers appear near the soil line
on older plants. As inner stem tissue is invaded, it becomes brick
red. |
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Pythium
Root Rot and Wilt, caused by Pythium sp., are characterized
by colorless to dark brown wet rot near the soil line. Young plants
and sometimes older plants wilt and die. Stems are hollow and feel
like soda straws. |
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Thielaviopsis
Black Root Rot, caused by Thielaviopsis basicola is characterized
by a dark brown to black rot of the taproot. |
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