Avocado trees are prized for their fruit and dense foliage, but their leaves are frequent targets for pests that compromise the tree’s health. When damage appears, accurate identification is the first step toward successful management. Recognizing the injury pattern—whether the pest chews the leaf tissue or siphons out the internal contents—guides the selection of the most effective strategy.
Chewing Pests: Caterpillars, Grasshoppers, and Beetles
Damage caused by chewing pests is often the most noticeable, characterized by the physical removal of plant tissue. Caterpillars, the larval stage of moths, cause significant defoliation by eating entire leaf portions. These larvae frequently tie leaves together with silk strands to create sheltered feeding nests, leaving behind ragged edges or large, irregular holes.
Beetles, such as the Fuller rose beetle, feed by chewing on the foliage, typically at night. They often leave distinct, notched, or scalloped edges on the leaves, particularly targeting new, softer growth. Grasshoppers are daytime feeders that cause large, irregular sections of the leaf to disappear entirely. While mature trees tolerate some leaf loss, young trees may suffer significant growth setbacks.
Sucking Pests: Mites, Thrips, and Scales
Sucking insects use specialized mouthparts to pierce the leaf surface and extract cell contents, resulting in discoloration rather than missing tissue. Mites, such as the six-spotted mite, feed primarily on the underside of the leaves. Their feeding leaves characteristic stippling—tiny yellow or white dots—which can progress to a bronzed or bleached appearance. Mite infestations may also be identified by fine silk webbing.
Thrips, including the avocado thrips, damage the leaf surface by scraping and sucking, especially on immature leaves. This results in silvery or bronzed scarring and distortion of new growth. Scale insects attach to stems and leaves, covered by a waxy coating. They extract phloem sap, reducing tree vigor and producing honeydew, which promotes black sooty mold that impairs photosynthesis.
Mollusks and Vertebrate Feeders
Foliage damage can also be attributed to non-insect pests, including mollusks like snails and slugs, which are nocturnal feeders. These gastropods leave behind ragged, irregularly chewed holes. Their presence is confirmed by the shiny silver trails of dried mucus left on leaves and surrounding surfaces.
Larger vertebrate animals also consume avocado leaves, causing more significant damage. Deer tend to clip young shoots and terminal ends of branches, resulting in large, clean cuts. Rabbits gnaw bark and foliage on young trees, typically causing damage lower to the ground. Iguanas can strip softer, newer leaves completely.
Integrated Strategies for Pest Management
Effective management relies on an Integrated Pest Management (IPM) approach, prioritizing non-chemical methods before targeted intervention. Cultural controls optimize the tree’s environment to naturally deter pests. Proper irrigation and fertilization maintain a vigorous tree better able to tolerate and recover from minor pest damage. Pruning to improve air circulation and removing leaf litter or weeds that harbor pests are also important sanitation practices.
Physical and mechanical controls offer immediate, hands-on solutions for managing larger pests. For chewing insects like June bugs or snails, night-time inspection allows for hand-picking and removal. Placing barriers, such as copper tape around the trunk, deters mollusks. For sucking pests, a strong jet of water can physically dislodge mites and thrips from the leaf undersides.
Biological controls leverage natural enemies. Lady beetles and parasitic wasps help keep scale and mealybug populations in check, while predatory mites control pest mites. Avoiding broad-spectrum chemical sprays is important because they often kill beneficial insects, leading to pest resurgence.
Chemical intervention should be a last resort, focusing on low-impact, targeted options. Horticultural oils or neem oil are effective against many sucking insects, like mites and scales, by suffocating them. For serious caterpillar infestations, a product containing Bacillus thuringiensis (Bt) can be applied, as it only affects the feeding larvae.