Gesellschaft für Phytopathologie mbH Konstanz

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Apple scab / Venturia inaequalis

Apple scab is the most significant fungal disease in apple cultivation, not only in ecological but also in integrated production (IP). In order to keep the pathogen at bay, up to twenty fungicide sprayings are required per season. A good effect with efficiency levels of over 90% is essential. We offer you product testings at different application times, but also experiments concerning miscibility (tank mix) or compatibility of preparations.

Disease lexicon

In vivo greenhouse experiment

Apple plants are inoculated with the pathogen in the greenhouse by first washing conidia from scab-infected leaves and spraying them on the test plants. By default, the scab population is derived from trees not treated with fungicides and is sensitive to the common fungicides. From fungicide resistance tests also scab populations with different resistance status are available (link resistance test). Inoculation is carried out on the first three fully developed leaves of a shoot in each case. For infection with Venturia inaequalis, the plants are kept moist in a mist chamber for at least 20 hours after inoculation.

Depending on the problem, the fungicide treatment is carried out protectively (eighteen hours before inoculation), as a stop spraying in the germination window of the fungus (five hours after inoculation of the wet leaf or under watering) or 24 hours curatively (wet or dry leaf). Protectively effective preparations can additionally be checked for rain fastness by watering the treated plants with a defined amount of water after surface drying of the spray deposit. After watering, the artificial inoculation is then carried out. If required, dose-response curves with the desired number of concentrations can be generated for the respective application methods. Approximately 20 days after inoculation, the scab symptoms are evaluated on the three leaves that are the youngest at the time of inoculation. The experiments are carried out with five shoots per variant and repeated once. The percentage reduction in scab lesions compared to the untreated control is calculated as the efficiency.

Hand-grafted potted trees of the Jonagold variety inoculated with the scab pathogen in the greenhouse.

In vitro germination test

In order to get a first indication of the effect of a preparation, you can have us perform germination tests. In the process, conidia are washed from untreated apple trees. In the variant with the test preparation, the product is added to the pathogen suspension in the desired concentration. Following a one-day incubation at 20°C and 100% relative humidity, the germination rate of Venturia inaequalis is determined microscopically. The efficiency is calculated from the germination rate of the test variant compared to the untreated control.

Disease lexicon

Germinated scab conidia