APS Homepage

POSTERS: Chemical control

Higher rates of phosphonate improve efficacy against scab on pecan
Michael Hotchkiss - USDA-ARS-Southeastern Fruit and Tree Nut Research Laboratory. Kory Herrington- University of Georgia, Timothy Brenneman- University of Georgia, Clive Bock- USDA ARS, Southeastern Fruit and Tree Nut Research Laboratory

Venturia effusa causes scab on pecan in the southeastern USA. In susceptible cultivars, frequent fungicide sprays is the only option to control the disease. Resistance to some fungicides has made management challenging. Understanding how rate affects disease control is important to ensure that control is maximized. We compared the effect of different rates of phosphonate products in reducing scab in six field experiments from 2015 to 2018 at two locations in Georgia. Cv. Desirable was used in four experiments, and cv. Wichita was included in two years at one location. Four rates of ProPhyt® (2.3, 3.5, 5.3 and 7.0 L/Ha), three rates of Rampart® (2.3, 4.7 and 7.0 L/Ha), or two rates of K-phite® 7LP (2.3 and 7.0 L/Ha) were tested. Also depending on experiment, 5 to 9 applications of phosphonate product were made. Incidence of scab was invariably high on fruit in the control trees, and most often high on treated trees. Treatment with the higher rates of phosphonate product most often significantly or numerically reduced severity of scab compared to the lower rates of the products applied on foliage and fruit. In 2015 fruit weight was increased where phosphonate application resulted in reduced disease, but in 2016 the effect was unclear due to a late and mild epidemic of scab likely having limited impact on the fruit size. Our results demonstrate that higher rates contribute to more efficacious control of this yield-limiting disease.