How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS AND SIGNS

Small branches and leaves can be killed, leaving entirely brown dry leaves that usually remain on dead limbs for months. Dead branches may retain fruit, which blackens and shrivels. When leaves are infected but are attached to healthy stems, leaves often are mostly green with necrosis only in brown patches along leaf margins and at tips. When stems are healthy, typically only some of the leaves on that stem have necrotic patches. Within a tree, usually only one or a few scattered stems have necrotic leaves, and all leaves on most branches will show no symptoms of infection.

COMMENTS ON THE DISEASE

Dothiorella leaf and stem blight is caused by several similar fungal species named in DOTHIORELLA CANKER. Dothiorella leaf and stem blight is a common disease of minor importance to the health of established trees. Stem and leaf blight commonly develops during hot weather and where irrigation is not adequately managed. Otherwise healthy trees tolerate scattered necrotic leaves and a few branches killed by Dothiorella disease. The primary concern is fruit and nursery stock health. Copious spores are produced on dead limbs and leaves. Spores inoculate fruit on the tree, sometimes causing significant fruit rot and stem end rot after harvest. Contamination of plant parts used for propagation can kill young trees because of infection of the graft between rootstock and scion.

MANAGEMENT

Prune off dead limbs and twigs during dry conditions and dispose of dead wood and old fruit away from avocado trees. Knock down groups of dead leaves stuck in trees. Maintain a thick layer of mulch to hasten decomposition of fungi on the ground. Use good sanitation and optimal cultural practices to minimize disease as discussed in DOTHIORELLA CANKER and DOTHIORELLA FRUIT ROT. When weather changes from cool to warm, appropriately modify the irrigation program, and pay special attention to irrigation needs during periods of hot weather.

PUBLICATION

UC IPM Pest Management Guidelines: Avocado
UC ANR Publication 3436
Diseases
B. A. Faber, UC Cooperative Extension, Santa Barbara/Ventura counties
A. Eskalen, Plant Pathology, UC Riverside
G. S. Bender, UC Cooperative Extension, San Diego County
Acknowledgment for contributions to Diseases:
H. D. Ohr (emeritus), Plant Pathology, UC Riverside
J. A. Menge, Plant Pathology, UC Riverside
L. J. Marais, Plant Pathology, UC Davis
R. Hofshi, Hofshi Foundation, Fallbrook, CA
J. S. Semancik, Plant Pathology, UC Riverside
J. A. Downer, UC Cooperative Extension, Ventura County
U. C. Kodira, Plant Pathology, UC Davis

Top of page