Citrus Leafminer

• The Asia citrus leafminer is an infrequent but troublesome pest of lemon trees. Originally from Asia, the leafminer has been found in lemon crops around the United States since 1993, according to the University of California. The Asia citrus leafminer larvae attack the new leaf development on all varieties of citrus trees. The damage prevents new leaves from opening properly, and the damage caused from feeding makes lemon trees more vulnerable to secondary diseases such as cankers. Leafminers reproduce rapidly and may produce seven to eight generations in a single growing season that can cause significant damage to lemon trees if left untreated. Citrus oil sprays are effective at controlling Asian leafminers on lemon trees.
  
  

Scales

• California red scale and yellow scale are small insect pests that feed on lemon trees. The two species of scales are difficult to distinguish from one another. Yellow scales are found primarily on lemon fruits and leaves while red scales are can be found on mature wood as well as fruits and leaves, according to the University of California. Scales feed on the plant tissue of the tree with their long, penetrating mouth-parts. In large numbers scales can severely damage lemon trees.
  
  

Citrus Rust Mites

• The citrus rust mite, commonly called the silver mite on lemon trees, is a small pest that damages the surface of lemon fruits. The citrus rust mite is a very small, yellow insect that requires a hand lens to see on lemon trees. The mites feed on the surface of lemon fruit and destroy the rind cells. Infested lemons fade to a silver color on the tree. Rust mite damage on young fruits reduces their overall size and appearance, but on mature fruits the damage is primarily aesthetic and the fruits remain viable.
  
  

Spider Mites

• Spider mites feed on mature leaves of lemon trees. These small insects receive their common name due to a fine silk that the mites produce while feeding on lemon trees. Spider mites feed below the leaf surface and cause cellular damage, reducing the ability of an infested lemon tree to photosynthesize. Large numbers of spider mites may cause a lemon tree to wilt and drop its leaves, especially during dry and windy growing seasons, according to the University of Florida.