RESEARCH & EVENTS
Alternaria leaf spot
LEAF spotting was observed in many NSW almond orchards during summer . Eryn Lehman from Yenda Producers Co-operative said the spots often darkened into necrotic spots or an irregular shaped burn within the leaf or along the margin . Heavily infected leaves fell off and in severe cases resulted in significant defoliation of the trees . Samples from several locations were tested and Alternaria leaf spot was frequently isolated from the samples , despite the symptoms having a different appearance to typical expression of Alternaria . Alternaria species are present in Australian orchards and all almond varieties are susceptible . Symptoms were first observed on ‘ Nonpareil ’ but have since been found on other common varieties in the Riverina . The Integrated Disease Management team working on AL22002 suggest orchards should be inspected for signs of the disease from October to December , especially if infection has been seen in previous seasons . However , there can be several weeks from the initial infection to the expression of the disease . The pathogen overwinters as spores in the tree and on plant material on the orchard floor . The spores are dispersed by wind and rain landing on new growth in the spring . Infections occur during extended dew periods or high humidity with warm summer temperatures , it doesn ’ t
necessarily require a rain event for the initial infection . Severe symptoms can be seen where there is little airflow and high humidity . Young orchards in the Riverina were more heavily affected during the 2023-24 season compared to mature orchards . Growers are advised to follow best management practices for disease , particularly after several wet springs , which have resulted in increased level of disease pressure . Regular fungicide sprays , particularly from bloom into spring , using a both systemic and protective chemistry will help provide protection against many common diseases affecting almonds , including Alternaria . A disease severity value model has been developed in California for Alternaria leaf spot and growers are advised to apply fungicide if the accumulated index values over a seven day period reach 10 or higher . More than 200 products are registered in Australia to control Alternaria leaf spot in almonds . These products can be found by using the keywords ‘ Alternaria ’ and ‘ almond ’ in the search function on the Australian Pesticides and Veterinary Medicines Authority ( APVMA ) Public Chemical Registration Information System Search . A factsheet about Alternaria leaf spot can be found on the ABA website .
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Alternaria leaf spot was observed in many NSW orchards during the summer .
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