jan-feb-2021

IN YOUR ORCHARD THE ALMOND BOARD How to Control Fungal Canker Diseases Contributed by Florent P. Trouillas, Associate Cooperative Extension Specialist in the Department of Plant Pathology at the University of California, Davis Fungal canker diseases are common problems in almond orchards. Infections caused by canker pathogens often results in bark and wood cankers, leading to profuse gumming near the affected area and eventual girdling and loss of an entire scaffold branch or tree. Our laboratory recently investigated fungal canker diseases affecting California almonds, with the major canker diseases recognized including Botryosphaeria canker (commonly known as band canker) and Ceratocystis canker, as well as Cytospora canker and Eutypa canker. 1 With continued support from the Almond Board of California (ABC), we conducted additional research and field trials that aimed to develop control strategies against almond canker diseases. Recently, we established management guidelines to help growers limit the incidence of fungal canker diseases in almond and promote tree health in the orchard. Cultural, Environmental Risk Factors A common lifecycle of fungal canker pathogens involves spores being released from fruiting structures (pycnidia or perithecia) on the dead wood of infected plant hosts during rain events and then being spread via rain or wind to fresh wounds and openings in the bark. In almonds, fungal canker diseases usually originate at pruning wounds or wounds resulting from mechanical injuries from field equipment to trees’ trunks and branches. Cracks at the tree crotch or on the trunk can also serve as additional entry points for canker pathogens. A critical operation in almond production that presents a high risk of infection is pruning, especially pruning associated with the selection of primary and secondary scaffolds that will provide the future tree shape and structure. Scaffold selection occurs soon after planting and limbs not selected for the tree framework are cut away, leaving large pruning wounds on trees. Large wounds near the trunk make trees particularly vulnerable to infection, and any infection of the trunk by a canker pathogen can lead rapidly to tree death. Similarly, maintenance pruning of mature trees – made to improve light interception and air circulation in the canopy, or to facilitate the passage of field equipment – can also lead to large pruning wounds on trees. This is an example of Botryosphaeria canker developing at a pruning wound made for secondary scaffold selection. Photo courtesy of Florent P. Trouillas. 1 For more information on symptoms, causal agents and infection processes associated with these diseases, please visit www.almonds.com/almond- industry/industry-news/main-fungal-canker-diseases-affecting-california-almonds. 4 0 A L M O N D F A C T S