Lime Tree Leaves
My lime tree has a dark powder all over its leaves. I also noticed a few crawling bugs, but I am trying to use environmentally friendly products. I live in Ewa Beach, HI, dry side of the island.
Certified GKH Gardening Expert
It's called sooty mold and is common on citrus trees. While unsightly, it's usually harmless. The mold grows on the sweet honeydew from sap-sucking insects like aphids, scale bugs, etc. You'll first need to treat the offending insect pest (hosing off plant and using garlic spray, insecticidal soap, neem oil, or other horticultural oil). Here is an article that you may find helpful: https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm
If you need help in determining the culprit or treatment, check out these articles: https://www.gardeningknowhow.com/plant-problems/pests/homemade-aphid-control-a-natural-way-to-kill-aphids.htm