Beware of these avocado diseases

Stem canker, Phytophthora root rot and anthracnose are among the main diseases likely to affect your avocado trees.

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Root rot, caused by Phytophthora cinnamomi, is the most serious and important disease of avocados worldwide. P. cinnamomi has more than 1 000 hosts, including many species of annual flower crops, berries, deciduous fruit trees, ornamentals, and vegetables. Locally, it’s found in all production areas, as well as home gardens. The severity of infection varies, but the potential loss is very big if no control measures are taken.

Root rot

Root rot likes soil moisture and poor drainage. Trees of any size and age may be affected. “The pathogen is easily spread through movement of contaminated nursery stock […] on equipment and shoes, in seed from fruit lying on infested soil, or by any activity by people or animals that moves moist soil from one place to another,” says the Division of Agriculture and Natural Resources, University of California.

Phytophthora produces four different spore stages that are involved in disease development and survival: sporangia, zoospores, chlamydospores, and oospores. They spread rapidly in water, moving over or through the soil. Entire areas can become infested. Phytophthora species are not true fungi but have many fungal-like attributes.

Where Phytophthora is present, leaves are smaller, paler in colour, turn yellow, wilt, and then drop off, and the entire tree assumes a bare appearance.