Apple scab / Venturia inaequalis
The disease caused by Venturia inaequalis is the most important fungal disease in apple cultivation. The scab pathogen is increasingly developing resistances to the active agents. The specific active agents from the following groups: sterol biosynthesis inhibitors (difenoconazole, fluquinconazole, penconazole, flusilazole, tebuconazole), anilinopyrimidines (cyprodinil, pyrimethanil, mepanipyrim), strobilurins (trifloxystrobin, pyraclostrobin, kresoxim-methyl) and succinate dehydrogenase inhibitors (boscalid, fluopyram, cyflufenamid, fluxapyroxad) are chiefly at risk of resistances. Evidence of less sensitive scab populations can also be found in the literature for the active ingredient dodine. To determine an appropriate strategy for scab control in your orchard, it is advantageous to know the resistance status of your scab population. In order to analyse the sensitivity of the scab population in your orchard to the products applied by you, just send us approximately 100 leaves infected with scab from your apple orchard (see sample route sheet). If you would like ascospores to be tested, please contact us.
For the in vivo scab experiments, conidia and ascospores are isolated from the leaves and potted apple trees are inoculated with the scab pathogen. Treatment with fungicide is carried out either before or after inoculation in different concentrations, depending on the active agent. The scab symptoms are evaluated two to three weeks after inoculation.
Protective active agents (fluxapyroxad, trifloxystrobine, dodine, captan, dithianon) could be tested in-vitro by mixing scab conidia and the preparation to be tested and counting the germination rate of conidia via microscope.
The effect of the active agent concentration used is calculated and the dose response relationship is compared with the baseline sensitivity. Through the test and, if necessary, a modification of your spraying schedule, you can optimize the protection against leaf scab and fruit scab in your orchard.
