Not mold, but more likely something the nursery or grower sprayed on the tree. Could be an insecticide (organic or not), could be a chelated micronutrient spray. Can you wipe it off with a damp cloth? And yes, you've got a pretty chlorotic tree. More fertiizer (Meyers tend to need more fertilizer due to bearing so heavily, as you've found out.) I assume that sprinklers are not hitting this tree, and that you do not have grass under the tree? Both of these can cause issues with citrus. Citrus do not like to be hit by sprinklers, this can promote fungal infections. And, grass under the tree will compete with nitrogen, and the grass will extract the nitrogen before your citrus tree can get to it, so if you do have grass, be sure to remove the grass out to the drip line or a bit beyond, so the tree can get to the fertilizer and actually take it up.

Patty S.

Can you post a photo of the whole tree? If it were my tree, I would certainly treat it with a fungicide. Is it underfed?... probably. Can a tree this size support 50 lemons?
Certainly, if it gets fed properly.

It's not the best image for diagnosis purposes. I wonder if powdery mildew might be a possibility? Plant diseases are becoming more and more resistant to chemical fungicides due to overuse, so I wouldn't apply a fungicide until a positive ID has been made.

You'd probably find some good advice at your local UCCE office. I would expect that your county would have a very active program.

John, highly unlikely this is a fungus. It looks more like a film of some sort. Not powdery mildew either, Rhizo, I have never seen it on my citrus here (and San Diego and I live in the same area), but have plenty of the dang stuff on some of my more susceptible roses (we're in "powdery mildew" country here near the coast). What it looks like to me, is the residual of Merit coming off the tree (which can stay stuck for a while), based on the tree getting sprinkled with water. We've had some rain (surprisingly), and that's why I asked about San Diego's sprinkler situation - could be getting sprinkled by sprinklers or by a hose? Pretty sure it's nothing to treat, but just a leftover film from something used by the grower or nursery. Before getting concerned about an infection, maybe if San Diego could snap a closer up photo so we can see the white stuff more clearly?

Patty S,

Thanks Patty, John and Rhizo -

The white substance wipes right off. I took a picture of the whole tree, but wasn't able to get anything closer up that was clearer than picture #1. I can't imagine it's something from the nursery, since it's been in my yard for over one year. I noticed a little bit of this on my lime today too (about 10 feet away). There are no sprinklers that hit my tree. Everything is done from a bubbler at ground level. A few months back, John suggested adding more fertilizer due to yellow leaves -- still yellow but it keeps sprouting fruit although it never fully ripens. It reminds me of a powdery mildew but I wasn't sure and if so, I didn't know if I needed to treat it. There is mulch under the tree and some grassy plants nearby, but not close enough to reach the root base of my lemon tree.

It stinks to have so much unripe fruit. I just want to get my tree healthy again. The tree looked fabulous until all the flowers turned to seed/fruit in the spring.

Thanks again for your thoughts - Christina

You have a lot of fruit on that tree; but the newer growth has a very good color; so it is probably getting enough food now. Don't expect those yellow leaves to get green again; they will eventually fall off when the tree has sucked everything out of them that it can. The initial cause of the yellowing, as I might have told you was lack of food and lots of fruit, causing the tree to cannibalize the older leaves to use the nutrients for new leaves and fruit.

Don't stress about the ripening; those fruits will get ripe and turn yellow (in your area) around mid November. If you want, you can use some of them before they are ripe; a half mature Meyer is still a better lemon than most of the competition.

Thank you John!

Exactly what John said :-) Your tree looks fantastic, the white film is most like left over from the nursery or grower, not to worry. And, all those gorgeous Meyer lemons will ripen, not to worry. Great looking tree, those older leaves will probably drop off to be replaced by new flush. You're right on track.

Patty S.

I have the same. It started like that, now it covers the whole tree. I think it's powdery mildew. Mine washes off too. The ants love it.

Any pictures?