The Q&A Archives: Grapefruit Tree Infestation

Question: I have recently moved into a home which has a beautiful mature grapefruit tree in the yard. It is March and the blossoms are just about to open. I noticed upon inspection of the leaves, two distinct problems. There is a black powdery substance on many leaves, and there is also some white patchy areas as well. I would like to know what I can use to treat these problems and keep them from returning, and if I can do it now at this pre blooming stage. I want the tree to do well since there is an abundance of flower buds getting ready to open. Thank you in advance for your help.

Answer: The stuff you are seeing is called sooty mold. Certain pesky insects, including whiteflies, scale, or aphids secrete a substance known as honeydew which supports the growth of the black, sooty mold.

Control the insects with sprays of an appropriate insecticide such as insecticidal soap or a lightweight, horticultural oil. Direct sprays upward from beneath the plant making sure to wet the undersides of all leaves and branches. Repeat spraying will likely be necessary to get the pests under control.

When you control the pests, the sooty mold will cease to be a problem.

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