purchased a new Minneola Tangelo a couple of months ago. I noticed that the undersides of some of the leaves appeared to be stained a deep orange color when I got home. The vendor I purchased it from mentioned that the tree had been under sun lamps at his nursery so I figured that the discoloration was due to sunburn. This afternoon, I noticed that some leaves on my other trees were “rusting” on the bottom as well….”it” appears to be spreading.

Coincidence or not, but I also discovered that one of my other trees was infested with red mites – I mean, there must have been thousands of them that I could see. I could run a single leaf through my fingers and mash 20 of them in a single pass. I did not have a single mite all of last year which makes me think that maybe I brought them in with the new trees that I purchased. I blew as many off as I could with the garden hose and then once dry, sprayed with Fertilome Triple Action Plus and a little hort oil. I’ll repeat this again in 7 days.

Is there a connection between the mites and leaf discoloration or are they two separate occurrences? If the later, what in the world is causing the discoloration of my citrus tree leaves? Photo’s below:







Thanks and best,

Skinn30a

My in-ground orange got very similar spots on the under side of few leaves. I think they are signs of frost damage since they developed after a light freeze we had.

Let's wait for expert opinion though.

Good luck!

I'm not an expert by any stretch, but it does look like sunburn to me:

http://www.ipm.ucdavis.edu/PMG/W/A-CI-WEAT-FR.012.html

Bump

Did you freeze protect them with water? Some of my trees have leaves that looks similar, but didn't show symptoms for a week or so after having to protect them from the cold. My problem was due to not being able to adequately apply water at a high enough rate due to the wind blowing while it was so cold. The water couldn't release enough heat and damage to leaves occurred.

The other possibilities may be some type of salt spray injury from being near a beach, or rust mites (since they were there).

similar spots appeared few years ago after light freeze on one of my seedlings.

https://imagizer.imageshack.us/v2/585x439q90/341/foto0027hf.jpg

Skinn, I live near the coast, the temperatures are always above 0º C (32º F), no freezes here (well, no exactly, maybe 1 or two slight freezes per year).
But my zone is very windy and several of my citrus have leafs like yours, with orange stains in the undeside.
As far as I know and I read in forums, these stains are induced by strong winds combined with cool temps.
But don't worry, it is not a disease or pest and your plant will grow well.
By the way, only some of my new potted plants suffer of this. None of my inground trees have these stains. In my opinion it is favoured by the contrast from a better environment to other no so good, cooler and windier. Probably, the plants will adapt better for the next winter.

that is right. This is nothing to worry about. This happens only to newly planted seedlings, not trees. The next winter those spots did not show.
The thing that confused me, why did they appeared at all, because the lowest i had that year was 1 C. The cause is probably what axier said, combination of low temperatures and cold wind.

Thank you fellas!

Soooo... Finally found out what's discoloring the bottom of those leaves... it's Elsinoë australis, the fungus that causes Sweet Orange Scab. Some friends of mine that are studying @ VT took a sample back with them when they visited over the holidays and the results just came back to their lab yesterday...

Fairly new disease as it was 1st confirmed in Texas during 2010.

The source of my infection was a Minneola Tangelo that I purchased from Flying Dragon citrus nursery (located in Jacksonville, FL) in January of 2013.

Too bad. I'm going to have to touch base with my county extension and see what they want me to do.

Best,

Skinn30a

frost damage would be better option.