The Q&A Archives: Citrus Leaves Turning Yellow

Question: I have two young dwarf orange trees - a Cara Cara Pink, and a Trovita. I bought them both last fall, and planted them both in large containers, with a mixture of potting soil and shredded bark.

For a long time they were fine. But early this year the leaves started turning yellow (from the veins outward) and falling off. At first I thought they might be missing some micronutrients (I had already given them some fertilizer), so I gave them something called "Citrus Growers Mix", which has iron, copper, etc. No change. Then I thought perhaps I was overwatering them, so I really cut back on the watering. But the problem remains. It's not bad enough that I think the trees are in any *immediate* danger of completely defoliating, but if this keeps up long enough they will be. The leaf-loss is quite noticable on the Cara Cara, in particular.

Also, the Cara Cara is flowering a bit right now, but the flowers are smaller than they were before, and many of them are quite brownish. It seems obvious that the tree is under stress, but I don't know why or what I did wrong or what I can do to fix it. I am also pinching off the old flowers, in an effort to reduce the stress on the tree (I can wait for fruit). But I'm still very worried - what else can I do? We have had an unusually cool and cloudy February, if that makes any difference.

Any advice would be greatly appreciated, thank you,

Barbara Connors

Answer: Several things could be wrong. When young leaves (those near the end of shoots) turn yellow, we ususally consider an iron deficiency to be the cause. High pH, high phosphorous and of course low soil iron levels all can result in iron deficiency symptoms. If older leaves are yellowing, nitrogen may be deficient. However, with iron or nitrogen deficiency, the leaves usually do not fall from the plant.

Root problems are a more likely cause. Root rot infection, physical damage to roots, drought and overwatering (soggy, waterlogged soil) can all cause leaves to turn yellow and fall.

Try to determine which of the cultural problems listed above may be the cause and take steps to alleviate it. If a root rot disease is present, there may be little that you can do at this time other than to avoid overwatering which tends to make things worse.

Another possible culprit is Citrus Mesophyll Collapse. Grapefruits are particularly susceptible but any citrus may be affected. Leaves and fruit of citrus trees dry up and drop. Stems and branches remain green and living. Rarely is the whole tree affected. Mesophyll collapse occurs when there are unseasonable weather changes. For example if it gets abnormally cold in October for several days and then heats back up above average temperature in November. This fluctuation stresses the trees as they kick into and out of and then back into their winter slow down. It is especially stressful after a dry summer.

I hope the information above will help you determine the cause of the problem with your citrus trees. If all else fails, take a sample to your local Extension Service for an accurate diagnosis and treatment recommendation. (909-683-6491)

Good luck with your citrus trees!

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