RESEARCH & EVENTS
Lower limb dieback in Australian orchards
By Brittany Oswald ( South Australian Research and Development Institute ( SARDI ), Plant Research Centre , Urrbrae , South Australia ) and Mark Sosnowski ( School of Agriculture , Food and Wine , Waite Research Institute , The University of Adelaide , SA )
LOWER limb dieback ( LLD ) has been a major concern for almond growers in California ( Doll , 2015 ) and Australia ( Wiechel et al ., 2022 ). International research has not definitively determined the cause of LLD ( Lampinen et al ., 2009b , Michailides et al ., 2010 ) and no research has been conducted in Australia . This study aimed to determine the prevalence of LLD and investigate the potential causes . During general disease surveys from 2018-2020 in Australia , a dieback severity rating scale was developed , and trees were assigned with a disease severity rating to better discern whether there were differences in symptom severity between trees of different ages ( Wiechel et al ., 2022 ). In the current study , LLD symptom expression and progression were intensively monitored in several South Australian orchards in each spring from 2019 to 2021 . These intensive studies were conducted to observe how symptoms progressed on a range of tree ages and cultivars . Several possible causative or contributing factors of the dieback syndrome were investigated , including light , tree age , cultivar , and trunk disease pathogens .
Continued next page
A
C
Typical LLD symptoms A . Yellow leaves appearing in the lower canopy . B . Dead branches in the lower canopy . C . Central staining . D . Wedge-shaped canker in symptomatic branches .
B
D