The Q&A Archives: Grapefruit tree disease?

Question: I have a mature grapefruit tree that has a couple of problems. I'm pretty sure it has sooty mold, as there is black powdery substance on the leaves, but the leaves also seem to have squiggly white lines growing through them and the leaves are deformed. Some of the branches are totally dead, but some are not. It does have blossoms on it and in years past, even with these diseases, has had fruit, which has discolored skin (probably from the mold, I'm guessing as it can be washed off) but still tasty, although it does have less fruit as time goes on. I've fertilized it, sprayed with copper and insecticides as well as used a feeding type spray. what is wrong with it and what else can I do?

Answer: Judy,

Your tree is suffering from more than one ailment most likely. The sooty mold is a sign of certain insects such as scale, aphids, mealybugs or whiteflies. Summer oil sprays can help keep these in control if you follow label instructions for mixing and applying them, making sure to get thorough coverage when you spray. Repeated applications will be needed as oil sprays are not poisons but rather smother the pests and don't provide residual control. You never contact all the pests with one application and those that survive are the primary reason for retreatments a couple of time at 2 week intervals.

The squiggly lines may be due to leaf miners which are not a cause for concern. I suggest taking some samples from you tree to your County Extension Office for diagnosis and control suggestions.

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