Reduction of scab incidence (Venturia inaequalis) in apple with prohexadione-Ca and trinexapac-ethyl, two growth regulating acylcyclohexanediones

Prohexadione-calcium and trinexapac-ethyl, inhibitors of 2-oxoglutaric acid-dependent dioxygenases, were tested for their efficacy in controlling scab infection on apple (cv. Golden Delicious) scions under greenhouse and field conditions. Their effectiveness was compared with other types of growth inhibitors (chlormequat chloride and paclobutrazol). Furthermore, to determine the time required to build-up plant resistance against scab, the compounds were applied at different concentrations and timings prior the inoculation with Venturia inaequalis. Prohexadione-calcium and trinexapac-ethyl significantly reduced scab incidence starting approximately 10 and lasting for approximately 25 days after application. In field conditions, the practical application of these compounds may result valuable both to control the vegetative/reproductive balance of the trees and to effectively reduce the amount of fungicides used to control scab.