Question
QUESTION: I have several oleanders (red and white), their leaves are turning yellow and dropping off in large numbers

ANSWER: Hi Tom, more info, where are you located, how old are they, how much water do they get, any evidence of the Oleander Caterpillar...let me know. Nick

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QUESTION: Nick,
  The Oleanders seem to have stopped dropping leaves since last week,( I believe I overwatered) I inspected carefully and have found no evidence of insects. I live in s.w. Florida,they are about 16 months old (about 7-8 feet tall,about 18" tall at time of planting.)

Answer
Hi Tom, I think you asked me about palms in another question, overwatering could very well cause defoliation if the roots are not draining off adequately. Oleanders are pretty tough customers, so ease off the irrigation but watch for the caterpillars..Nick