I suspect that the black spots that you are finding under the leaves are the result of insects. Often lace bugs are the culprit, but again without looking I cannot be sure. Regardless, using insecticidal soap according to the label directions will likely take out whatever the insect is. Gibb, Entomologist The information given herein is supplied with the understanding that no discrimination is intended and no endorsement by the Purdue University Cooperative Extension Service is implied. Any person using products listed assumes full responsibility for their use in accordance with current direction of the manufacturer.
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