Answer:Oleanders seem to be a favorite host of scale insects, and they can really do damage to the plant if left unchecked. If you only recently sprayed horticultural oil, the timing was less than perfect and your plant is suffering the consequences. Oil will suffocate scale insects, but it will also coat the leaves, and at this time of year (midsummer) will intensify sunlight on leaf surfaces and suppress the ability of the leaves to transpire. The drooping is a result of these actions. The residual oil will eventually weather away through repeated rainfalls.
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