Grapefruit Tree Disease - Knowledgebase Question

Wildomar, Ca
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Question by fbksfoxylady
February 10, 2011
I have a grapefruit tree that has several small soft nodules of a sticky white substance with a small brown spot that is on the branches or leaves. It turns the branch black if left on for any length of time. There is a sticky thread like secretion from it. The leaves below these nodules turn black and are sticky when this secretion falls on them.

How do I treat this to get rid of it?

Answer from NGA
February 10, 2011
Without seeing the problem I'm only able to offer an educated guess. I suspect your tree has a population of scale insects. They look like brown bumps on the branches - or clusters of brown bumps. As scale insects feed they exude a sticky material (called honeydew) which has a high enough sugar content that it turns black as it ages. This black residue is called sooty mold and it can usually be scraped off the surface of a leaf, or washed off. If you control the scale insects, the sooty mold will weather away over time. Neem oil based pesticides will usually suffocate scale insects. They will eventually deteriorate and fall from the branches. Be sure to apply according to label directions so you don't harm your tree.

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