Increasing High Quality Production of Organically Grown Apples Through a System’s Approach Including Management of Vf Scab Resistance

van der Maas, M.P.
Wageningen University and Research (WUR), Department of Applied Plant Research (PPO), Randwijk, Netherlands

Gross organic apple production/ha and percentage class 1 is too low to ensure increase in percentage of organic grown apples in the Netherlands. On the experimental orchard in Randwijk (WUR/PPO) a system approach was tested to increase high quality production and reduction in use of organic pesticides, especially against apple scab. The new varieties ‘Santana’ and ‘Topaz’ were used. These varieties are Vf scab resistant and have low risk of biennial bearing.

A scab resistance management system was developed to prevent loss of scab resistance. Only 5 to 10 sprayings of sulfur per year against scab and mildew were applied (Dutch standard is 20 to 30 sprayings) and no other organic pesticides such as copper and sulfur lime against scab and mildew were used. It appeared that ‘Santana’ was not susceptible to rosy apple aphid and other aphids. Other pests and diseases were controlled according to the Dutch organic standard.

After 7 years the orchard was still scab free although scab was present in other organic orchards with Santana in the vicinity of the experimental orchard. Other experiences with scab Vf resistant management show the additional importance of spacial barriers besides fungicide treatment at infection peaks.

Gross production of the experimental orchard in Randwijk was high (average 45 ton/ha for Santana and 37 ton/ha for Topaz in the 3rd to 7th growth year) in comparison with the Dutch average (20-25/ha). The average percentage of class 1 fruit over the years for Santana was 69%. For Topaz the percentage of class 1 dropped from 75-79% in the first three years to 25% in the last year. This was due to russeting of the stem cavity.