Q. New growth on my African sumac has curled leaves and it looks like aphids or something is attacking them. I thought sumacs were desert trees and didn't a have a lot of issues so I'm surprised by this development.
A. African sumac does get aphid problems. Aphids are more of a problem during cool weather and the problem usually disappears with the heat. But aphids will hang around during the heat and cause problems as well. A good indicator of aphids is the presence of ants.
If the aphid problem is bad enough you may see leaf yellowing and leaf drop, sticky or glossy leaf surfaces. The stickiness is aphid excrement which is sugary and attracts the ants.
Soap and water sprays will get them under control if applied every few days. Soapy sprays do not hang around very long.
Or you can use a systemic insecticide applied to the soil around the base of the tree and watered in. The poison moves up the tree to the leaves and poisons the aphids. This may be safer to use and more environmentally friendly than spraying the entire tree with a pesticide.
Remember that African sumac is a very messy tree with lots of leaf drop. If you don't want a mess, you might not want African sumac.