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Disease

View three presentations concerning threats posed to California avocado groves by new pests and diseases, including laurel wilt disease, fusarium dieback disease, the polyphagous shot hole borer and the Florida redbay ambrosia beetle.

A new beetle that vectors a Fusarium dieback on avocado trees has been discovered in and near Los Angeles County. The newly discovered polyphagous shot hole borer beetle is indistinguishable from the tea shot hole borer beetle and is believed to be a new species of beetle.

Healthy avocado roots play an important role in producing consistent high-quality avocado crops from healthy avocado trees. Roots provide nutrients and water for strong healthy leaves, good shoot growth, flowering and fruit set, and avocado fruit growth.

Phytophthora mengei (P. citricola) and P. cinnamomi have been associated with trunk canker and collar rot of avocado. The pathogen infects the crown, lower trunk and limbs of older trees. The disease develops after crowns, limbs, or trunks become infected through wounds, such as injuries from equipment, pruning, vertebrate chewing, and wind damage.

The measures recommended for the control of Phytophthora avocado trunk canker disease are similar to those described for Phytophthora root rot. In fruit, prevention of infection is challenging because it is likely caused by the splashing of Phytophthora spores from the soil surface to the fruit during rainy weather.

The primary means of managing avocado branch canker disease is applying chemical treatment to any open wounds to prevent Botryosphaeriaceae spores from entering and initiating infection.

A California avocado tree canker that occurs on twigs, branches or trunks is caused by a complex of fungal pathogens which include many species in the Botryosphaeriaceae family. Canker pathogens can enter and initiate infection through wounds on the bark surface, such as pruning, frost damage and mechanical injury wounds.

Since no definitive measures have yet been found to control the disease, an integrated approach to managing the root rot disease has been found to be most effective. This approach includes root rot prevention, avocado grove cultural management practices and chemical treatment.

Phytophthora cinnamomi, the causal agent of avocado phytophthora root rot, attacks the feeder roots, which can result in death of the avocado tree. Although the disease has been studied for more than 60 years, definitive control measures have not been found and losses continue to mount.

Raffaela lauricola, the causal agent of laurel wilt disease (LWD) is a devastating pathogen that has the potential to greatly impact the California avocado industry. Laurel wilt is a vascular wilt disease that has led to substantial mortality on trees in the Lauraceae family since it was first found in the southeastern United States in 2004.

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