Yucca extract effective against scab in apple cultivation

Researchers of Applied Plant Research (PPO), a part of Wageningen University and Research Centre are involved in intense cooperation with various European partners for the purpose of durable scab control in organic apple cultivation. Apple scab is caused by a fungus (Venturia inaequalis) and is a major economic issue in all areas where apples are grown. The disease mainly develops in cool, rainy conditions in the spring, and the resulting spots can make apples difficult to sell. Furthermore, early leaf loss generates indirect damage by reducing the vitality of the trees.

The researchers studied the effects of yucca extracts in the laboratory as well as in the orchard. When examining apple seedlings in the laboratory, researchers found that the extract had both a preventive and a curative effect. The extract achieves the former by preventing the fungus from budding and thereby from infecting the plants. A curative effect is also active until at least one day after the plant is infected by the fungus.

The extract was shown to be promising in practice as well during field tests in a PPO orchard in Randwijk, the Netherlands, and another orchard in Denmark. The effects were found to be as good as those of a low dose of copper. While organic growers in Europe currently depend primarily on copper, sulphur and lime sulphur to fight scab, copper is no longer allowed in the Netherlands, and the European Commission has decided to ban the use of copper throughout Europe.

This study took place under the auspices of the EU project Repco (project nr 501452), which stands for Replacement of Copper in Organic Production of Grapevine and Apple in Europe, and is partly financed by the 6th Framework programme of the European Commission. The goal of this project is to find alternatives for copper in the organic production of grapevine and apples.