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POSTERS: New and emerging diseases

Phytophthora palmivora: Another threat to English lavender in the United States
Daniel Dlugos - Clemson University. Steven Jeffers- Clemson University

English lavender (Lavandula angustifolia) is one of the most widely grown lavender species worldwide. Phytophthora root rot (PRR) was reported on L. angustifolia at a nursery in the U.S. in 1991, and Phytophthora nicotianae was identified as the pathogen. PRR has now been reported around the world on multiple species of lavender and is caused by several species of Phytophthora. Since 2015, we have collected samples of lavender plants with PRR symptoms from 25 states in the U.S., and P. nicotianae has been isolated most frequently. However, P. palmivora was also isolated from L. angustifolia plants from multiple states. Previously, this pathogen has been reported on L. angustifolia only in Italy and Turkey. Two isolates of P. palmivora and one isolate of P. nicotianae isolated from roots of L. angustifolia plants were used to test pathogenicity. Four-month-old plants of L. angustifolia ‘Hidcote’ were inoculated with individual isolates or were used as non-inoculated control plants. Plants were grown in a greenhouse for 9 weeks and evaluated weekly for foliage symptoms. At the end of the trial, multiple disease parameters were measured. The plants inoculated with either P. palmivora or P. nicotianae developed typical PRR symptoms and had some mortality, and both pathogens were isolated consistently from diseased roots. Control plants remained pathogen- and symptom-free. Therefore, P. palmivora is capable of causing PRR on L. angustifolia and poses another threat to lavender production in the U.S.