Severity of scab in tall pecan trees sprayed using ground-based air-blast, or aerially applied fungicide

C.H. Bock, M. Hotchkiss
Yield loss in pecan due to scab (caused by Venturia effusa), and the cost of sprays to manage the disease are major economic constraints to profitability in the southeastern USA. Scab is most often controlled by multiple fungicide sprays applied using an air-blast (AB) sprayer (as many as 10 applications or more). Some growers also apply fungicide aerially (A), but usually only a few sprays (1 to 3 applications) are made as supplements to the AB applications. Distribution of scab in the tree canopy using these two methods has not been established. In this study, severity of scab at 5 heights (5.0, 7.5, 10.0, 12.5 and 15.0 m) was compared using AB, A, and AB+A applications, and compared to a non-treated control in 25-m tall 'Schley' trees in 2013 and 2014. Control trees had most severe scab at most heights, except >12.5 m, where severity in trees receiving the AB spray was most often similar. However, severity at <12.5 m was lower in the trees receiving the AB spray compared to the control. The A application most often had lower severity at all sample heights compared to the non-treated control, but the difference compared to the AB treatment was not always significant at 5 to 7.5 m. The combination of AB+A treatments had uniformly low severity of scab at all heights. Spray coverage was measured on water sensitive cards at each sample height. Results indicated a decline in spray coverage with height using the AB sprayer, but A applications resulted in uniformly low spray coverage at all heights. In conclusion, AB and A sprays controlled scab, but there was a failure in efficacy of AB sprays at heights >12.5 m; A-treated trees tended to show a slight increase in disease severity low in the canopy.
Bock, C.H. and Hotchkiss, M. (2021). Severity of scab in tall pecan trees sprayed using ground-based air-blast, or aerially applied fungicide. Acta Hortic. 1318, 191-200
DOI: 10.17660/ActaHortic.2021.1318.28
epidemiology, disease management, disease control, Venturia effusa

Acta Horticulturae