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purple / black spots

Posted by jonathandb wa (My Page) on
Tue, Apr 10, 07 at 18:26

I wonder if any one has an idea what is going on with this otherwisw healthy rhododendron? The under side of some of the leaves have light purple blotches, on the upper leaf surface corresponding to the purple blotches are dark purple/black blotches with some brown.
Any ideas thanks.

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RE: purple / black spots

  • Posted by morz8 Z8 Wa coast (My Page) on
    Wed, Apr 11, 07 at 21:01

There are about 10 different fungi that can cause leaf spot on rhododendron...and while I haven't seen it here near the coast, powdery mildew is becoming more common on our rhododendrons.

Leaves infected with powdery mildew may become off color and exhibit the white powdery fungus growth associated with the disease, or some rhododendrons lack the white powder and instead show yellow or purplish spots on the upper leaf surface and discolored areas on the lower leaf surface.

My advice without a picture to show us would be to take example leaves exhibiting the symptoms to staff at a reputable nursery (not a box store) or county extension agent for an accurate diagnosis. Funginex sprayed at the appropriate time can be helpful and I've heard Bayleton recommended too since it's systemic and can be easier to apply to large shrubs - but it's expensive so best to know for sure what you are treating.

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