Lime Trees & Mold

Lime trees often develop sooty mold.

Sooty mold often occurs on lime and other citrus trees, causing a black moldy growth on the tree. Sooty mold is primarily cosmetic and does not usually damage lime trees or fruit.

Identification

Sooty mold is a fungal disease that causes black, sooty fungus to develop on trees. Rubbing your fingers across the leaves of trees with sooty mold removes the mold temporarily. Sooty mold is caused by insects, such as aphids and scales, that produce a substance called honeydew, which causes mold to stick to leaves, branches and fruit. The presence of sooty mold is an indication that trees are heavily infested with insects.

Symptoms

Sooty mold causes black mold, which is similar in appearance to chimney soot, on the leaves, twigs, branches and fruit of affected lime trees. A heavy covering of sooty mold can cause trees to suffer from a lack of sunlight, causing limes to be discolored.

Management

Apply horticultural oils to wash away sooty mold. Insects must be eliminated to keep sooty mold from reoccurring. Spraying lime trees with a hard stream of water often causes insects to fall from the trees. Continue to spray affected trees with oil to keep insects from returning.

References

• University of Florida: Citrus Problems In The Home Landscape; Mongi Zekri, et al.; July 2010
• University of Arizona: Diagnosing Home Citrus Problems; John Begeman, et al.; April 2009