Brown bumps on underside of Phalaenopsis leaves

[Ray]

I use Acephate when the plants are outdoors or in a separate greenhouse (it really stinks!). If you can get a water-soluble imidacloprid product, that’ll work well, as well. Concentrated azadirachtin products are also effective.

In all cases, I spray all the plants, wetting all exposed surfaces to dripping, and thoroughly drench the potting media. Do that three times at one-week intervals.

If, within about a month, you see a return, repeat that regimen using an insecticide with a different MOA.