Michigan State University Extension
Ornamental Plants plus Version 3.0 - 00000501
11/12/99
DELPHINIUM DISEASE PROBLEMS
Black leaf spot causes irregular, shining, tar-like spots
on the upperside of the leaves. The spots are brown on
the undersides of the leaves. The petioles, stems and
flowers may also be attacked. The lower leaves are
attacked first. The disease spreads in cool wet weather.
Remove infected leaves when noticed and cut off and
discard old stems. The disease is caused by Pseudomonas
delphinii.
Soft crown rot is also called delphinium black leg. It
occurs during hot, humid weather and enters through
wounds. The crown and roots decay causing rapid wilting
and death of the plant. Decayed plant parts have a foul
odor and a soft black discoloration is seen at the base of
the stem. Avoid excessive watering. This problem is
caused by Erwinia carotovora.
Diplodina crown rot causes a crown rot noticeable after
the plants have grown for two or more seasons. Infected
plants may winter kill or produce shoots which later rot
at the base. The disease is worse when moisture is
excessive and the tissues are succulent.
Crown rot caused by Sclerotium rolfsii causes sudden
wilting and death of the plant. The lower leaves become
wilted and badly infected plants are easily pulled up.
Avoid sites known to be infested.
Stem canker begins as one or more small brown spots on the
stems. The lower leaves turn yellow with the yellowing
progressing upwards. When advanced, the flower spike
droops and the leaves curl upwards. Remove infected
plants. The causal organism is Fusarium oxysporum var
delphinii.
Powdery mildew causes a white powdery growth on the
leaves.
A number of leaf spots are found on Delphinium. Some of
the most common are caused by fungi in the genera
Cercospora and Septoria.
During periods of low temperatures with wet soil the
leaves may be chlorotic. This is a physiological rather
than a pest problem.
Related information.
Pesticide Recommendations
Powdery Mildew
Fungal and Bacterial Leaf Diseases
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This file was generated from data base ZZ on 01/19/00.
Data base ZZ was last revised on 11/12/99.
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