Apple Replant Disease
Apple trees may grow poorly when planted in non-sterilised soil. This poor growth is most frequent when apple orchards are replanted but may also occur when apple is planted in soils which have not previously grown apple.
- Affected trees have a reduced root system that results in poor growth and cropping, particularly during the early years after planting.
- The root system is reduced mainly because of the effects of several Pythium species.
- Apple variety/rootstock combinations vary in their susceptibility e.g., Cox, Golden Delicious or James Grieve on M.9 rootstock are more likely to suffer replant problems.
- More vigorous variety/rootstock combinations such as Bramley on MM.106 are much less likely to be affected.
- Previously it was possible to test potential new orchard sites for replant disease, but the test is no longer provided as a service.
- Soil fumigation pre-planting can reduce the effects of replant disease. The most effective fumigant is chloropicrin, which can only be applied by contractor. Pre-planting drenches with formalin are also usually effective.
- Treatments other than soil sterilants include placing peat compost in the planting hole or using trickle irrigation, or soil mulches or a combination of these.
- Replanting in the areas that were the alleyways of the previous orchard offers an alternative approach, which may reduce the replant problem.