Citrus Leaf Drop in the Low Desert

PLANTS MOST SUSCEPTIBLE: Citrus trees

SYMPTOMS:

Leaves turn yellow and fall off

CAUSES & MANAGEMENT:

Some leaf drop is normal for citrus particularly in the late winter/early spring as new leaves are pushing out. Heavy leaf drop could be due to a variety of circumstances:
• CAUSE: Over fertilization
  
  MANAGEMENT: Prevent by following fertilizer application instructions on the product. Treat by watering heavily to flush the fertilizer below the root zone.

• CAUSE: Inappropriate watering strategy, too much, or not enough
  
  MANAGEMENT: As a general rule citrus need a deep watering once a month in the winter and once a week in the summer. Apply water to the entire root zone, well out beyond the drip line. Apply enough water to wet the soil at least a foot below the surface. Check the depth of the irrigation with a long handled screw driver, you will only be able to push the screw driver as deep as the water has gone.

• CAUSE: Citrus Mesophyll Collapse: Grapefruits are particularly susceptible but any citrus may be affected. It is not uncommon for grapefruit trees to be affected and other nearby citrus to be fine. 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.
  MANAGEMENT: Remove fallen fruit to prevent attracting fungal and bacterial diseases. Continue to water the tree on its normal cycle and it will leaf-out again in the spring. Do not prune out the defoliated branches until spring, and then only after the tree has completely leafed out.

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