White Fuzzy Coating on Sour Orange Leaves: Powdery Mildew or Salt?

A white, fuzzy coating on sour orange leaves that appears in cooler weather could be powdery mildew—or it could be salt exudate from saline soil, common in Arizona. Powdery mildew typically forms discrete fuzzy patches, not a full-leaf coating, and causes yellowing and early leaf drop. Salt crusts often cover most of the leaf surface and feel gritty.

How to Tell the Difference

• Powdery mildew: Wipes off as dry powder; leaves yellow and drop.
• Salt deposit: Feels crystalline; does not wipe off cleanly; common in high-salinity soils with poor drainage.

Next Steps

Take a few affected leaves to a local independent nursery that specializes in citrus. They can distinguish between the two and recommend appropriate action—fungicide for mildew, or leaching and soil amendment for salt buildup.