Birds, squirrels, and rats are fond of avocados and can destroy large quantities of fruit. Birds prefer immature fruit; rats and squirrels tend to prefer mature or nearly mature fruit.

This plant disease is caused by a fungus (Pseudocercospora purpurea) that infects avocado leaves and fruit. Old leaf infections are the usual source of spores. In some years, much leaf loss can occur, weakening the tree and slowing fruit development. When the fungus attacks the fruit, the spots often provide convenient entryways for other fungi that rot the fruit.

This disfiguring disease is caused by a fungus (Sphaceloma perseae) that is carried over from one season to the next on stem and leaf lesions. Young fruits are usually infected just after the petals fall from the flowers. As fruit ages, it becomes more resistant to infection, but it does not acquire immunity until it is more than half-grown.

Sabulodes caberata This worm, the larva of a brown night-flying moth with a wingspan of up to 2 inches, attacks avocados and other trees and shrubs. Although the moth is nocturnal, it may be found during the day on the undersides of leaves, where it lays eggs. The larvae that hatch from these eggs feed on the foliage and developing fruit for about 6 weeks. Then they pupate inside leaves that they web together. Larval damage occurs year-round but is most severe during the spring and summer.

This plant disease is caused by a soil-inhabiting fungus (Phytophthora cinnamomi) that infects many fruit, nut, and ornamental trees and shrubs. It penetrates the roots and crown of the tree. As the fungus decays the sapwood, the flow of water and nutrients is blocked, eventually resulting in the death of the tree. The fungus is spread by infected plants and by infested soil and soil water. Phytophthora root rot is greatly favored by wet or poorly drained soil. Trees planted in lawns, flower beds, or other moist or poorly drained areas are highly susceptible to this fungus.

This insect is a common pest of avocado. The four-winged adult lays eggs on the undersides of leaves. The larvae are the size of a pinhead, flat, oval, immobile, and semitransparent. In about a month, they change to the winged adult form. The larvae are more damaging because they suck more sap from the plants than do the adults. They cannot digest all the sugar in the sap, and they excrete the excess in a sticky material called honeydew, which coats the leaves and may drop from the plant onto surfaces below.