En EspaŅol

Q. Who is Mr. Smarty Plants?

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.

Help us grow by giving to the Plant Database Fund or by becoming a member

Did you know you can access the Native Plant Information Network with your web-enabled smartphone?


Ask Mr. Smarty Plants

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

Search Smarty Plants
See a list of all Smarty Plants questions
Can't find the answer in our existing FAQs, submit a question to Mr. Smarty Plants.
Need help with plant identification, visit the plant identification page.
rate this answer
Not Yet Rated

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


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?


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.


More Diseases and Disorders Questions

What's that sticky stuff on plants under many trees?
August 23, 2010 - Here in Austin, I've recently noticed a sticky film appearing on shrubs, flowers, grass, etc. under many trees. It appears to be coming from the trees under which they are planted. The sticky film ...
view the full question and answer

Problems with Escarpment black cherry from Ponder TX
February 11, 2011 - I have an escarpment black cherry that is about three years old and about 9 feet tall. It was healthy until this last summer when its began to bark peel and sap run out at the base of the tree. The af...
view the full question and answer

Why is my Mountain Laurel in distress?
November 26, 2008 - We have planted our 2nd Texas Mountain Laurel in the same spot (after fresh berm built with sandy loam) and it is not looking good in less than 2 weeks. We have an identical berm on the other end of...
view the full question and answer

Northern Catalpa Tree Doing Poorly
July 02, 2014 - One of our Northern Catalpa trees appears to be dying. It is about 28 feet tall and this year only about 1/3 of it is producing leaves. It is next to our largest Catalpa tree (about 65 feet tall and a...
view the full question and answer

Whitefly infestation in roses and salvia
June 15, 2007 - Several of my outdoor plants (including Knockout roses and salvia) have a white residue on the stems. If I touch it a white bug jumps off. The residue can be wiped off or sprayed off, but the little...
view the full question and answer

Support the Wildflower Center by Donating Online or Becoming a Member today.
© 2015 Lady Bird Johnson Wildflower Center