Black Leaves On Lemon & Lime Trees - Knowledgebase Question

San Francisco, CA
Avatar for kerstin4
Question by kerstin4
November 8, 1999
I just bought my first house, and there are lemon and lime trees in the yard. The leaves are covered with a black fungus -- it looks almost like the trees are covered in mud -- and the fruit is rotting on the trees. I also noticed bumps that look a bit like scale. What can I do to make the trees healthy again?

Answer from NGA
November 8, 1999
Scale insects can cause problems, as you've discovered. When they, and other sucking insects, feed, they leave behind a sticky substance called honeydew. The sugar content of this honeydew is just high enough to promote fungal growth called sooty mold. While sooty mold in itself is not harmful, it looks bad. Once you get rid of the scale insects, the sooty mold will weather away in rain and wind.

Begin by pruning back any obviously dead or damaged limbs and branches, and removing the fruit. Then spray all parts of your tree with a horticultural oil. The oil will suffocate the scale insects. If the ripe fruit is turning light brown and soft, brown rot fungus might be at work. Fungal spores can splash from infected fruit to sound fruit during rains. The best defense for this is to remove and destroy infected fruit. Once the health of your trees is restored, they should produce attractive, tasty fruit.

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