AVRDC International Cooperators'
Alternaria Leaf Spot
Alternaria brassicae, A. brassicicola
Most crucifer plants are susceptible to Alternaria leaf spot and
plants at all growth stages may be affected. Symptoms
caused by the two pathogens are very similar and both may
be found on the same plant. Infection of seedling stems may
result in damping-off or stunted plants.
Leaf spots vary in size from pinpoints up to 5 cm in diameter.
Typically lesions begin as small yellow areas that enlarge to
about 1.5 cm in diameter and are dark colored spots with
concentric rings. A brown discoloration of cauliflower and
broccoli heads is caused by infections with these pathogens.
The pathogen causes elliptical necrotic spots on seed stalks
and seedpods. Pod lesions may extend into the pod interior
and attack the seed causing them to shrivel.
Numerous circular spots
on Chinese cabbage leaf
Close-up of lesions
Conditions for Development
The pathogens are seedborne. They also sporulate profusely on debris from infected
plants, and persist on susceptible weeds. Alternaria is readily spread by wind. The
disease is enhanced by warm, wet weather with an optimum temperature between 25
Pathogen-free seed should be used. Hot water and chemical seed treatments are
effective. Fungicidal applications may be necessary when crops are grown in
conditions that are conducive for severe disease development. Avoid overhead
irrigation particularly with cauliflower and broccoli in which head rot may occur.
Last updated: 2001.
Information from: Vegetable Diseases: A Practical Guide. Lowell L. Black, AVRDC.
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