Pest of the Month – Bot canker, aka Ficus branch dieback
(Botryosphaeria complex)

* This pest is not currently in Hawai’i. AAA raises awareness of potential pest threats so that arboriculture professionals and residents alike can help our state monitor and identify pest problems when they arise.

Photos: University of California, Division of Agriculture & Natural Resources

Description
Opportunistic fungal complexes of the Botryosphaeria genus infecting Ficus and other stressed, wounded or predisposed trees and plants.

Distribution
The Ficus Bot complex was initially identified in southern California. Brotryosphaeria fungi are present in Hawaii, as are fungi in other genera the Botryosphaeriaceae family, though it is not known whether they cause branch cankers or dieback in Ficus.

Hosts
Indian laurel-leaf fig (Ficus microcarpa). Other Bot complexes also occur on grapevine, avocado, citrus, etc.

Symptoms and Damage
Canopy chlorosis, thinning and dieback, sometimes restricted to a particular branch; branch cankers; wedge-shaped discoloration of branches in cross-section, and black pycnidia on bark surface (see photo below). After a branch has been killed, a mat of black spores develop beneath the bark. Diagnosis must be confirmed by a plant pathologist.

Control
Optimizing cultural care to reduce plant stress is the most important control method. Stress is believed to increase risk of disease development. Spores are dispersed by splashing water or wind-blown droplets. Spores develop in dead bark. Control includes pruning out diseased or dead twigs and branches, and proper disposal of diseased material. Avoid pruning during wet weather. There is no research as to whether sanitizing / sterilizing pruning tools helps, however this is routinely recommended along with pruning with hand tools only (chain saws cannot be sterilized). According to pest control experts, phosphorous acid products in addition to currently available fungicides applied as a soil drench may be beneficial.

Additional Resources
“Disease Focus: The rise of Bot canker diseases,” University of California, Division of Agriculture & Natural Resources. Retrieved 08/14/2017 from: http://ucnfanews.ucanr.edu/Articles/Disease_Focus/DISEASE_FOCUS_The_rise_of_Bot_canker_diseases/

“Love them or hate them, ficus trees lining city streets are dying from a new fungal disease,” San Gabriel Valley Tribune, 6/17/2017. Retrieved 08/14/2017 from: http://www.sgvtribune.com/environment-and-nature/20170617/love-them-or-hate-them-ficus-trees-lining-city-streets-are-dying-from-a-new-fungal-disease