Fungus in Avocado Trees

Phytophthora Root Rot

• The Phytophthora cinnamomi fungus causes severe root rot in avocado trees. This soil-borne pathogen is the most significant disease affecting global avocado production, according to the University of California. Leaves of infected trees are often significantly smaller than normal and may have a yellow or brown discoloration. Branches and stems start to die as the fungi destroy large portions of the roots. Preventative measures such as sanitary cultivation practices and proper soil conditions can keep the fungi from establishing themselves.

Cercospora Leaf Spot

• Fungal leaf spot diseases are common ailments that affect trees, shrubs and herbaceous plants. Avocados suffer from Cercospora leaf spot, which is caused by the Cercospora purpurea species. The pathogen attacks the foliage of its host, causing small dark spots on infected leaves. According to the University of Florida, leaf spots caused by Cercospora are less than 3 millimeters in diameter, but they may grow into one another to form a larger, solid area of decay. This leaf spot disease can also damage ripening fruit.

Avocado Scab

• The Sphaceloma perseae fungus is the pathogen responsible for scab disease, an ailment that affects both the leaves and the fruit of the avocado tree. The fungus causes rough patches to form on the fruit. The spots are often purple or brown, according to the University of Florida. Scab can also infect avocado leaves, causing small spots and open holes in damaged foliage. An infection of fungal scab rarely causes serious damage, but it does encourage the growth of other pathogenic fungi.

Anthracnose

• Anthracnose of avocado is the result of an infection of the Colletotrichum gloeosporioides fungus. This pathogen only infects the fruit of its host and can ruin a significant portion of the tree's fruit if it's left untreated. Infected fruit has brown and black spots that expand quickly. The fungus decays the surface and inside of the fruit, rendering it unsuitable for consumption. According to the University of Florida, avocado anthracnose cannot establish itself on a tree without exploiting damage caused by other diseases, like Cercospora, or mechanical injury.