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Poster: Epidemiology: Risk Assessment


Incidence and severity of Phytophthora disease and assessment of inoculum levels in Texas citrus orchards
S. CHAUDHARY (1), M. Setamou (1), O. Alabi (3), J. daGraca (1), M. Kunta (1), V. Ancona (1) (1) Texas A&M Kingsville Citrus Center, U.S.A.; (2) Texas A&M Kingsville Citrus Center, U.S.A.; (3) Texas A&M AgriLife Research and Extension Center, U.S.A.; (4) T

Phytophthora foot and root rot disease, caused primarily by P. nicotianae, is present in Texas citrus orchards but there is a lack of information on the incidence and severity of the disease in the State. In addition, Texas citrus growers lack information on relative levels of P. nicotianae inoculum which are needed to make treatment decisions based on established thresholds. To address these knowledge gaps, a survey was conducted from February to June of 2015 across the three-county of Rio Grande Valley region where commercial citrus orchards in Texas are located. Twenty-four grapefruit, two tangerines and four sweet orange orchards were surveyed. 20 trees per orchard were rated for foot rot and gummosis lesion severity on a scale of 0 (no lesion) to 5 (entire trunk covered with lesion and gummosis). The survey revealed that 96% of Texas citrus groves are affected by foot rot and gummosis with the disease severity index ranging from 1 to 57 %. Further analysis revealed that 20% of the surveyed citrus orchards had more than 50% disease incidence with an average disease severity of 23.6%. Phytophthora propagule counts in the soil ranged from less than, five to 118 cfu/cm3 with 46% of orchards having more than the reported damaging levels of 20 cfu/ cm3. The data will be useful to growers for making treatment decisions and in predicting yield losses in the region due to foot rot and gummosis.