Q.sap from coconut palm
I have had two coconut palms in the front yard for about 7 years. Recently, I have noticed a sap residue on my auto whenever parked under the palms and then a deposit on other plants under the branches. It is like a black sticky soot and has discolored the leaves. The palm itself has all the branches turned blackish and most of the green is gone. It is still producing coconuts and new growth.
Certified GKH Gardening Expert
It sounds like sooty mold, which is caused by fungus growing on the sticky substance (honeydew) exuded by insects such as aphids, scale, or whitefly. This is relatively easy to get rid of by controlling the insects. Neem oil helps with both. Read more here: https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm