Leaves Yellowing on Calamondin Citrus Tree

Q. What causes leaves to yellow and black spots to develop on leaves of my calamondin citrus tree? I had them for seven years and they just now developed these yellow leaves with black spots. Nursery information desk advised picking off all affected leaves (but there are too, too many) then spray with cooper fungicide.

A. Combined with leaf yellowing, it sounds like either a nutrient or watering problem or both, not a disease problem. Copper sprays like Bordeaux Sprays, are usually recommended for disease control but I don't think that is it.

This is photinia but you get the leaf yellow idea from this pisture.

Try this:

    1. Cover the soil with 1/4 inch of rich compost or compost plus some fertilizer high in nitrogen

    2. Then cover the compost or compost/fertilizer with woodchips

    3. Apply a citrus fertilizer in January

    4. Try adding an iron fertilizer (I suggest an iron chelate called 133 or iron EDDHA)

This is the most effective iron treatment (EDDHA chelate) but it is more expensive than other iron chelates. Apply it in the spring (February) or no later t
han early summer (April/May) for best results.

If these citrus trees are in rock mulch, then it's a nutrient and drainage problem. Auger four or five holes into the ground, 2 feet deep and 1 to 2 feet from the trunk, to improve drainage. Fill these holes with soil mixed 50/50 with compost and an iron fertilizer.

Citrus fertilizers contain plant nutrients in higher concentrations than other plant nutrients particularly when these fertilizers are formulated for the desert Southwest like Arizona's Best and Grow Well brands.

            

Mix iron chelate with the compost before using it to fill the augured holes. Water once a week through the augured holes, filling them with a hose. Also, try spraying the leaves with an iron chelate solution four or five times, a few days apart. If this is an iron problem, even though it’s caused by poor drainage, the leaves should begin to get darker in color.

Put about four of these holes about 18 to 24 inches from the tree trunk  and 2 to 3 feet deep to improve drainage. If they are filled with gravel or woodchips they will stay open. They act as drainage sumps (French drains) around trees (vertical mulching).

Nutrient problems can be caused by poor drainage. That's why I'm giving a recommendation to improve the drainage using vertically augured holes and combining it with a compost and iron application at the same time.