Citrus leaves discoloring, even with Foliage Pro

I’ve been using Foliage Pro for about 3 months, treating my container citrus trees every 10 days with Foliage Pro mixed at 1 tbsp in 2.5 gals water with 1 tbsp vinegar thrown in. The trees have responded nicely, and you can see in the photos of my Star Ruby grapefruit that the leaves have a nice dark green look. But on this tree (and one other) there is a strong yellow/brown tinge showing up in many of the leaves. I’ve seen this before I started using the Foliage Pro, but it’s really showing up now on this particular tree.

Could someone pinpoint the deficiency that would cause this kind of discoloring. I’ve looked at websites with citrus deficiency examples but haven’t seen this yet.

John, I’m really not one who can look at leaves and say that any specific micronutrient is in short supply. Too many of them look similar to me. I’m not even good at catching all the little details in the background of pics posted.

Is there any chance that the leaves that show this have recently been exposed to stronger light than they are used to? Citrus tend to be sensitive to changes in light levels. I know it’s August, but have they been exposed to larger than they are accustomed swings in cold or heat?

You said you’ve been using the Foliage Pro at basically production levels. Do you also have a timed release fert with micronutrients like the Osmocote Plus in the potting media at proper amounts? That’s what provides the micros, except for calcium, since they stopped adding that to their latest formulation. Also, timed release granules aren’t really time released. The rate they give off their nutrients depends heavily on temperature, and moisture. They become depleted much more quickly while the temps are high. If you use them, when was the last time they were applied?

Since you do use the Foliage Pro, and your plants appear to be lush overall, I’m going to assume you already know what planting media and size containers are appropriate for your containers, unless you say otherwise.

Also, if it is just some areas of those plants, is there any evidence of sucking insect or other damage on the stems leading to those sections, or under the leaves?

I’m known to fuss and worry over every little negative change in my container grown citrus.

Looks to be on sun exposed leaves so I’d agree it’s more likely heat stress than nutrient issue.


Sunburn makes sense. It’s been hot up here, we have long summers, and the leaves on the backside of this tree don’t have much of the discoloring, if any. But I have some other citrus that get as much or more sun and they don’t have this problem, perhaps certain varieties are more susceptible. Does anyone know which citrus varieties sunburn easiest?

And if I put some shade cloth over this tree, would the sunburn fade away or is it a permanent change to the leaf?

I’ve never seen tissue damage from burns be anything other than permanent. Your plant would still be okay, and those leaves can stay on because they still have area left that photosynthesis and transfer nutrients.

I don’t suspect that the burning took place gradually over summer because the trees adapt to gradual changes in the amount of sunlight. It’s more likely that the containers were either turned or part of the canopy or objects nearby had been moved so that they got a more sudden dose of increased exposure, or that as the sun’s angle has changed throughout the season, something was no longer providing shade.

I find that my own container grown citrus prefer to have at least their containers shaded to keep the roots from getting too hot in the summers. Otherwise, they could easily reach over 110 degrees in the soil. My plants too, prefer not to have full sun hit their leaves when they are in areas with much heat or reflected light coming from ground level, such as near pavement or the pool apron. Here I attempt to provide them with afternoon shade during summer. Our summer sun is also strong and hot.

Sunburn is permanent. Eventually those affected leaves will drop to be replaced by new flush, no worries. It tends to happen to newer, more tender leaves, and Muddy is right, it really isn’t cumulative, but can happen when “opportunity and preparedness” come together. In this case - newer leaves and some really hot and sunny days. This is more prevalent on younger trees, as older trees will have more canopy protection for those newer leaves. Shade cloth is a great idea for a younger tree, and if you can see the trunk also, it is wise to paint your trunk with 1/2 strength flat latex house paint as well, to avoid scorching the cambium. Cultivars most sensitive to sunburn are variegated cultivars.