Symptoms and Signs
Bot gummosis can cause branch cakers, dieback, and gummosis. Portions of trunks or branches will have dead outer bark located over a sunken canker. The dead bark may exude gum; the cambial layer of wood underneath the bark may be brown to yellowish. The canker may spread up and down the cambium in grooves with some faint, shallow, yellowish-brown discoloration of the underlying wood.
Bot gummosis can cause rapid decline and death of a tree. Young trees are especially susceptible if the affected tissues are not removed. Often the dead bark remains attached to the tree so tightly that it is not immediately obvious that it is dead. This dead bark has a more grayish cast than healthy bark.
Comments on the Disease
Unlike dry root rot, discoloring of bark by the pathogen is lighter and infected bark may ooze dark liquid. On the surface, Bot gummosis may have a grayish cast with dead bark that remains tightly attached.
Currently, the management of Bot gummosis on citrus may be achieved by pruning dead limbs and twigs and removing pruning waste from fields prior periods of rain. This strategy is based on results from studies on avocado and grapevine; however, the efficacy of those cultural practices has not been evaluated. Pruning wounds, mechanical injury, frost, and sunburn damage have been reported to serve as points of entry for spores in the Botryosphaeriaceae family on other hosts. In avocado and grapevine, spores are released from fruiting bodies present on branches or twigs and spread by rain splash and wind, typically between November and April. Currently, there are no effective fungicides that can be used by growers to prevent bot gummosis on citrus in California.