Apple scab

Apple scab / Venturia inaequalis

Apple scab is the most significant fungal disease in apple cultivation, both in organic and integrated production (IP). To keep the pathogen under control, up to twenty fungicide applications are necessary per season. Effective control with efficacy rates exceeding 90% is essential. We offer product testing at various application times, as well as trials on miscibility (tank mixing) and compatibility of formulations.

In vivo greenhouse experiment

Apple plants are inoculated with the pathogen in the greenhouse by first washing conidia off scab-infected leaves and spraying them onto the test plants. As a standard procedure, efficacy tests use a scab population derived from trees that have not been treated with fungicides and are sensitive to commonly used fungicides. Scab populations with varying resistance statuses are also available from fungicide resistance tests (link to resistance test). Inoculation is performed on the first four fully expanded leaves of a shoot. To induce infection by Venturia inaequalis, the plants are kept moist in a mist chamber for at least 20 hours after inoculation.

Depending on the experimental setup, fungicide treatment is applied preventively (eighteen hours before inoculation), as a curative spray during the fungus’s germination window (five hours after inoculation on wet leaves or under irrigation), or 24 hours after inoculation (on wet or dry leaves). For protective formulations, rainfastness can additionally be tested by irrigating the treated plants with a defined amount of water after the spray film has dried. Artificial inoculation then takes place after irrigation. If necessary, dose-response curves with the desired number of concentrations are generated for the respective application methods. Approximately 20 days after inoculation, scab symptoms are assessed on the three youngest leaves present at the time of inoculation. The trials are conducted with five shoots per variant and repeated once. The percentage reduction in scab lesions compared to the untreated control is calculated as the efficacy.

In vitro germination test

To get an initial indication of a product’s effectiveness, you can have us conduct germination tests. In this process, conidia are washed off untreated apple trees. The resulting suspension is pipetted onto microscope slides. In the variant using the test product, the product is added to the pathogen suspension at the desired concentration. After a one-day incubation at 20°C and 100% relative humidity, the germination rate of Venturia inaequalis is determined microscopically. The efficacy is calculated based on the germination rate in the test variant compared to the untreated control.