UC Riverside

Canker and dieback diseases are commonly caused by fungal pathogens and affect hardwoods which include ornamentals, native tree species, and agricultural commodities. A resurgence of interest and research in these diseases in the past two decades has determined that many of these canker and dieback diseases for a particular host involve multiple species of fungal pathogens both within and between fungal families, suggesting that canker and dieback pathosystems are more complicated than previously thought and thus the management of these diseases may be more complicated given the diversity of fungal pathogens involved. Therefore, we sought to determine the fungal pathogens involved in canker and dieback diseases of citrus and ultimately to develop chemical management strategies for these diseases in citrus in addition to a new, invasive pest-disease complex, Shot hole borer-Fusarium Dieback, affecting California sycamore in California.

The results presented in this dissertation identify a new canker and dieback disease of citrus, Eutypella canker of citrus, in the Desert Region of California caused by three species of Eutypella: E. citricola, E. microtheca, and a Eutypella sp. Fungicide field trials determined strobilurin fungicides to be most effective in reducing vascular necrosis caused by Eutypella species in addition to vascular necrosis caused by N. dimidiatum, the causal agent of Hendersonula, an established canker and dieback disease in the Desert Region. A new twig dieback and gumming disease of citrus, Colletotrichum Dieback, was identified in the San Joaquin Valley Region of California and is caused by Colletotrichum gloeosporioides and C. karstii. Fungicide field trials determined pyraclostrobin fungicides to be the most effective in reducing the prevalence of Colletotrichum Dieback symptoms. For the management of Shot hole borer-Fusarium Dieback, pesticide field trials determined the insecticide emamectin benzoate and the fungicides metconazole, tebuconazole, and carbendazim plus debacarb to significantly reduce shot hole borer attacks in infested California sycamore.

The results of these works establish the presence of two new canker and dieback disease of citrus in California and provide chemical management strategies for the control of these diseases in addition to the management of Shot hole borer-Fusarium Dieback.