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A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Tuesday - September 02, 2008

From: San Diego, CA
Region: California
Topic: Diseases and Disorders
Title: Mildew and rot in navel orange tree in California
Answered by: Barbara Medford

QUESTION:

I have a great navel orange tree that seems to have two problems. One of them looks like powdery mildew and the other is some kind of black rot. I have sprayed it several times to no avail. I live near the ocean in San Diego. Any suggestions?

ANSWER:

Citrus sinensis is a hybrid of ancient origin from Southeast Asia. At the Lady Bird Johnson Wildflower Center, we are focused on plants native to North America. However, we will see if we can find a resource for you to check and see if you can find a way to take care of your tree.

We found an excellent site on dealing with problems with the navel orange trees. We really tried to find one from California but couldn't, so you'll have to accept this Texas Cooperative Extension site, instead. Then, if you're dedicated to finding a solution, go to this site, "Diagnosing common citrus problems", and see what you can find that fits your situation.

As in a great many plant problems, especially, it would seem, with trees, plant stress gets a lot of the blame. One reference said that orange trees should be fertilized 6 times a year, starting in early March through August/September. Maybe your tree is just hungry. Or, if the trunk is not above the surface of the surrounding garden, or there is mulch spread over the root zone, the tree may be developing root rot or foot rot. Charming terminology. It look to us like the experts were pretty nonchalant about most of the problems with navel oranges, with comments like "not worth treating", etc. It's up to you to plow through that chart on citrus problems and see if it's worth it to you.

 

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