RESEARCH & EVENTS
Branch dieback in almonds
By Brittany Oswald and Dr Mark Sosnowski
IN recent seasons, almond growers have reported an increase in branch dieback in multiple cultivars across several regions. This past spring in particular saw, an increase in Monterey decline( Monterey leafing failure) in some orchards, and more widespread reports of general tree decline and branch tip dieback, especially in the Riverina. With so many different symptoms appearing at once, growers are asking the question: what is driving dieback? Dieback can result from a number of abiotic stress factors such as salinity, shading, irrigation practices, heat events, and nutrient imbalance. However, dieback can also be associated with fungal trunk and root pathogens, bacteria, viruses, and oomycetes such as Phytophthora and Phytopythium. Pathogens can invade and kill shoot, branch, trunk and root tissues, restricting water and nutrient movement through the tree. As part of the Almond Integrated Disease Management( IDM) project, samples have been collected from affected orchards to determine which pathogens are present. In September to November 2025, branch tissues from South Australia, New South Wales and the Riverina were targeted to investigate the dieback symptoms being reported in the field, and to determine how often wounded branches are colonised by trunk disease pathogens. More than 800 branches in different conditions were collected. Branches were sorted into three groups: 1. Intact, healthy branches with no wounding or dieback symptoms. 2. Cut branches or broken branches, caused by machinery or pruning( Fig. 1 a). 3. Branches with dieback symptoms, not associated with wounding( Fig. 1 b & c). Preliminary results show that several key trunk disease pathogens were isolated from orchards. These included Botryosphaeria, Diaporthe,
Figure 1.( a) A cut branch,( b) dieback not associated with wounding, and( c) dieback with leaves still attached.
Cytospora, Colletotrichum, and Fusarium species. However, pathogen populations differed between regions and depending on whether branches were wounded and symptomatic, or apparently healthy. Of the wounded branch samples collected, 75 % were colonised by trunk pathogens. Isolations yielded Botryosphaeria( 26 % of samples), Fusarium( 15 %), Diaporthe( 13 %), Cytospora( 11 %), and Colletotrichum( 7 %). Pruning wounds are well documented as important infection counts for these pathogens. Branches with dieback symptoms but no wounds also had high levels of pathogen recovery. Isolations yielded Botryosphaeria( 20 %), Cytospora( 18 %), Diaporthe( 15 %), Fusarium( 5 %), and Colletotrichum( 3 %). However, 37 % of these samples did not yield any known trunk pathogens, confirming that abiotic stress or other factors may be causing the dieback. In comparison, asymptomatic, undamaged branches had lower infection rates. Isolations yielded Botryosphaeria( 10 %), Diaporthe( 8 %), Fusarium( 7 %), Cytospora( 4 %), and Colletotrichum( 2 %). Notably, 60 % of non-symptomatic, undamaged branches yielded no identifiable trunk pathogens. This shows that while some fungi can live latently in healthy tissues, they are less common in symptom-free tissues. Overall, Botryosphaeria spp. were the predominant species detected in branch samples, but other key fungal species are also prevalent. Fusarium species were widespread across all regions. Although historically not considered pathogenic in almond branches, recent international research suggests some Fusarium species may be causing disease, particularly under stress conditions in young trees. Detections of Diaporthe spp. have increased from 12 detections in 2015-2024 to 65 detections in 2025, and the role that these species play in almond dieback diseases are currently being investigated. The sampling confirmed that dieback is complex, not always caused by pathogens, and likely involves both abiotic stress and pathogens. Pruning wounds remain a key risk point for infection. Trunk pathogens were present in 40 % of asymptomatic branches, supporting previous research suggesting that these organisms can remain latent before causing disease symptoms. Further laboratory identification and pathogenicity experiments are underway to clarify which of these potential pathogens are responsible for dieback in Australian almond orchards, what factors might be exacerbating the dieback and how vulnerable pruning wounds are to common fungal pathogens.
industry. australianalmonds. com. au
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