Insecticides

• Insecticides are used to control aphids, white fly, black fly, mealy bugs and scale insects. Cottony cushion scale is particularly hard to control. Generally, to control these pests the first line of defense an insecticide soap, followed by a water-soluble pesticide. If this is unsuccessful, an oil spray is used. The insecticide soap generally washes off the leaves readily, but the oil spray is designed to remain for days, sometimes weeks.
  
  

Fungicides and Bactericides

• Sooty mold thrives in the honeydew produced by juice-sucking insects like aphids and white flies. In most cases it can be washed off; however if the underlying insect infestation is severe then that must be addressed first. Sometimes an insecticide/fungicide soap will be used to treat both problems simultaneously. Residue can remain on the leaves, making them toxic until it is washed off.
  
  

Foliate Fertilizers

• Although not commonly used for adult citrus trees, foliate fertilizers can leave a mildly toxic residue on leaves between rainfalls. As with any other product, carefully consider any product used to treat a food-producing tree, or other plant.