The disease affects both the leaves
and stems; small, round lesions form on the leaves. These spots develop
whitish to brown centers, have a dark red to purple rim, and often show a
yellow halo. Occasionally, an infected stem will
grow six inches or more above the rest of the plants. This is due to the
production of growth regulating chemicals called gibberellins, produced by
the fungus.
The disease thrives in high
humidity and wet growing conditions.
Splashing water will easily spread the spores from leaf to leaf and
plant to plant. The key in controlling this disease
is to stop the spread of the spores. When frequent rains occur, a cover over the plant or
plants is one solution. Another approach would be to apply a protective copper
fungicide that would prevent the splashed spores from starting new
infections.
Infected plants will usually continue to
live. However, the severity of the disease is dependent upon the amount of
rainfall. Remove infected
leaves, and if appropriate, prune out infected stems. Then apply either a
copper fungicide or one with the active ingredient chlorothalonil (Bravo, Daconil). As new leaves emerge, reapply the
fungicide. In the future, if the disease is not severe, removing infected
leaves may keep the disease under control.
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