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Originally Posted by Orchid Whisperer
A reasonable question, and you can probably get an answer by e-mailing the manufacturer.
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That assumes the manufacturer has any knowledge of orchids!
Systemic insecticides do not penetrate the plant and stay the same chemistry; it is actually the plants' metabolites of the insecticide that stay present.
Most insecticides only kill adults, and the idea behind systemics is not to provide long term protection, but to kill newly-maturing adults that weren't killed with the initial spray. Read product labels, but most will recommend three treatments at 7-10 day intervals, so that ought to give us an idea of the longevity of the systemic effectiveness.
Boisduval scale is a tough one to knock out. I had a really bad infestation once, and I ended up applying imidicloprid, acephate, and kinoprene (insect growth regulator) together, three times at one week intervals. Every plant was thoroughly soaked and the potting media saturated, with a second round applied immediately each time to ensure thorough treatment and saturation.
It worked.