Willow Oak with Black Bark and Yellowing Leaves: Fertilization and Mold Check

A two-year-old willow oak shows blackened bark, poor growth, and light green to yellow leaves.

Primary Treatment

Fertilize with 10-10-10 at 1 lb per inch trunk diameter, scattered and watered in. This should restore leaf color.

Black Bark Diagnosis

Likely sooty mold growing on honeydew from aphids. Check if bark feels sticky. If so, spray foliage with Orthene (acephate) to control aphids. The mold itself doesn't harm the tree and will fade as the tree grows.