Q: Our orange tree has been indoors for the winter. The leaves now have a rust-looking deposit on them. It feels gritty when you rub the leaf. What can we do?
A: I’m reasonably sure the plant is infested with spider mites….your leaves look just like those on my plant
The best control is to spray with neem oil (click for sources) or horticultural oil (click for sources)…but you’ll also get control by taking it outside and letting beneficial mites build up a population to control the spider mites during the summer.