Plant Diseases/Hackberry tree
My tree is quite old. Very large. It has developed a black fungus, mold or something on the leaves. It has gotten on my white vinyl fence, plus my pompass grass and appears to have affected my crepe myrtle . Any suggestions as to remedy.
Sound like aphids or scale insects. Both will suck the plant juices from the leaves and twigs and excerete a substance called honeydews. Honeydew is high in sugar content and is sticky to the touch. Usually a black sooty mild will grow on the honeydew making everything black and sticky.
You can either spray the tree's foliage or use a systemic insecticide on the soil beneath and the tree will absorb the insecticide through the roots and take the insecticide to the leaves and twigs. Spraying a large tree can be difficult.
I would recommend that next spring you treat the tree with a product called Bayer Advanced Tree and Shrub Insect Control. This is an insecticide called a systemic. You apply the mixture to the soil around the tree and the roots will pick it up and transport the insecticide to the twigs and leaves and when the insect sucks the sap they are killed. Apply this in the early spring as the leaves are budding out. This treatment will last all year. Here is a web link to more information on this product. You should be able to buy it at your local nursery type store.