Have a postoak that has white powderlike substance on the leaves. Does anyone know what this is and what to treat it with? Also have peach trees that have the leaves turning orange with small holes but don't see any bugs. Is this spidermites or something else and what should I treat this with? Thanks

http://www.dirtdoctor.com/dallasnews.php?id=19
From the above link, I copied the following:
Foliar feeding the plant with any compost tea product will help. Also sprinkle some cornmeal on the surface of the soil and water. Cut back on the watering and fertilizing, but add a ¼” layer of lava sand. If the bugs persist use a q-tip and alcohol to kill them. Neem products sprayed and drenched on the soil will also help control mealybugs and other stress related pests.