Key culprit named but no quick fix for almond tree decline

Researchers have identified an aggressive pathogen contributing to the widespread tree death and production losses in almond orchards across Australia. 

PhD candidate and plant pathologist, Brittany Oswald at The University of Queensland's Queensland Alliance for Agriculture and Food Innovation said while multiple pathogens were causing root and trunk rot, one soilborne pathogen was a more significant problem.

“Phytophthora became a major focus for us once we started sampling,” Ms Oswald said. 

“It’s extremely aggressive, attacking the roots, weakening the tree and even killing it within a year or 2.” 

Initial orchard surveys for the national Almond Integrated Disease Management project found fungal trunk diseases Botryosphaeria cankers were widespread but not as severe as Phytophthora.

Symptoms caused by the pathogens include branch dieback, trees oozing sap and large patches of dead trees in orchards with no clear explanation. 

Ms Oswald said the challenge for growers was the disease causing the greatest impact changed year to year and region to region.

“After flooding in late 2022, Phytophthora dominated,” she said. 

“More recently, we’re seeing a resurgence of branch dieback caused by the fungal trunk diseases, so there is no one-size-fits-all solution.”

The research has also showed management strategies effective against one disease can worsen another.

“Reducing irrigation can lead to fewer fungal infections but more severe Phytophthora,” Ms Oswald said.

“That’s why a blanket recommendation like reducing irrigation by 25 per cent can backfire.”

Ms Oswald said prevention would be critical to mitigate future losses, particularly as the industry continued to expand. 

“One of the biggest opportunities is stopping these diseases from entering orchards in the first place,” she said.

“We need to understand whether pathogens are already present in young nursery trees before they’re planted.

“If we could identify infected trees before they reach the orchard, we could potentially prevent new disease introductions right at the start. 

“Our work has highlighted key areas and provided the industry with a much stronger foundation. 

“We are now considering an integrated approach to managing trunk diseases that could lead to changes in practice.

“Targeted solutions to ensure the long-term sustainability of the almond industry are a critical component of future research.”

Collaboration and acknowledgements