RESEARCH & EVENTS
Initiating research on replant disease : A starting point for Australian almond orchards
ALMOND orchard replanting is generally required after 25-30 years to maintain economical yields . In Australia , approximately 10,000 hectares of almond orchards will be over 25 years old within 10 years and will require replanting . Replant disease ( RD ) of orchards such as apple , almond and stone fruit trees including ++ peach , plum and cherry is a significant challenge in orchard reestablishment . Symptoms of replant disease include stunted growth , reduced vigour , poor establishment , and a decline in overall tree health . Affected trees may exhibit yellowing or bronzing of the foliage , reduced shoot growth , and smaller leaves . In severe cases , trees may die within a few years of planting . This phenomenon is poorly understood and its incidence and severity are hard to predict . Severity of RD is typically greatest in the first few years of a replanted orchard ’ s development ( Browne et al 2006 ). Several management strategies can help mitigate the impact of RD including soil fumigation , cover crops and soil amendments , rootstock selection and biological control agents . Soil fumigation with chemicals such as methyl bromide or chloropicrin can effectively reduce the population of soilborne pathogens . However , these chemicals can be expensive and have negative environmental impacts . Planting cover crops and incorporating soil amendments into the soil can help suppress soilborne pathogens and improve soil health . Choosing rootstocks that are tolerant to the pathogens associated with RD can help reduce the severity of the disease . Biological agents , such as beneficial microorganisms and nematode predators , can be used to improve tree growth and promote plant health in almond orchards . Research in the US has found that RD can be reduced by preplant soil fumigation , anaerobic soil disinfestation , a process based on microbial utilization of organic carbon and nutrient sources , and biofumigation . There is a need for a better understanding of RD and approaches for managing it with less dependence on environmentally harsh soil fumigation . In Australia , the current and future situation of RD is unknown . Monitoring of recently replanted orchards is required to provide clarity on the current prevalence and impact of RD before strategies can be implemented to manage it . As part of Hort Innovation funded AL22002 An Integrated Disease Management program for the Australian almond industry - Phase 2 , Agriculture Victoria researchers will collaborate with the ABA to identify recently replanted orchards . Over the life of the project , these orchards will be monitored for signs of RD by measuring tree growth and biomass through increases in canopy size . Photosynthetically active radiation ( PAR ) and trunk diameters will be measured annually and compared with greenfield plantings . If signs of RD are present putative biological and chemical causes will be investigated in collaboration with US researchers to enhance our
A 25-year-old orchard ready for replanting .
Pushed trees in burn piles at a Riverland orchard – preparing to replant .
understanding of the syndrome . If putative pathogens are isolated from RD affected trees pathogenicity experiments will be carried out in years 4-5 to prove Koch ’ s postulates . This information will determine if RD will be a problem in 2030s when a major area of orchards will be replanted and provide valuable preventative strategies to reduce tree loss during orchard replanting . Replant disease is a complex condition and may be a significant challenge for Australian almond growers , impacting the establishment and productivity of replant orchards . By understanding the factors contributing to RD and implementing appropriate management strategies , growers can minimize the impact of the condition and ensure the long-term success of their orchards . Ongoing research and collaboration within the industry are essential for developing sustainable solutions to this complex problem .
Browne , G . T ., J . H . Connell , and S . M . Schneider , Almond replant disease and its management with alternative pre-plant soil fumigation treatments and rootstocks . Plant Disease , 2006 . 90 ( 7 ): p . 869-876 .
industry . australianalmonds . com . au
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