Apple Replant Problem


		Apple Replant Problem Apple replant problem is a serious and common cause of poor growth and delayed cropping of apple trees planted in old orchard sites. It is caused by a complex of fungi, bacteria, nematodes and soil factors such as pH, moisture stress and insufficient available phosphorous for vigorous growth of young trees. Overcoming replant disease is critical for the successful establishment of high density orchards. Early cropping and high productivity are essential to recover the high cost of replanting. Prevention and Control Prevention of replant problems is much easier and more successful than control. There is very little that can be done to correct replant problems once the trees have been planted. The causes of apple replant problem on different sites are highly variable. Not all soils respond in the same way to the various pre-plant treatments. Thus a treatment that is beneficial in one orchard may have no effect in another. 1. SOIL TESTING BEFORE PLANTING Preparation for replanting orchards should start at least one year ahead of planting. Soil analysis is necessary to determine fertilizer requirements, and also if lime is required to adjust pH prior to planting. For information on tree fruit nutrition and lime application, refer to the tree fruit production guide. If a plant parasitic nematode problem is anticipated upon replanting, contact your crop management advisor for information. Commercial services are available to test soil samples for pathogenic nematodes. 2. CULTURAL PRACTICES Special attention to all cultural practices is important to obtaining good growth of young trees. Irrigation and mineral spray requirements are essential. Good weed control is important to reduce competition for nutrients and water. Trees must also be handled carefully and planted as early as possible. 3. SOIL REPLACEMENT Soil replacement with 20 L or more of new soil, or a well prepared steamed planting soil mixture, can be satisfactory alternatives to treating the planting site. New top soil should be tested for pH and salinity before use. It should not come from old apple plantings, and should not contain residual herbicides. Soil replacement with a ratio of 1 part peat to 2 parts planting-hole soil can also be a beneficial treatment. 4. PREPARATION OF SITE FOR CHEMICAL OR FERTILIZER TREATMENTS In preparing old orchard sites for replanting, remove as many old roots as possible. The area to be treated should be cultivated thoroughly before applying the soil chemical or fertilizer treatments. 5. FERTILIZER TREATMENTS Research in the greenhouse using potted apple seedlings has shown that growth can be significantly increased by phosphate fertilizer (11-55-0) in 80 per cent of the soils. Ammonium phosphate fertilizer (11-55-0 or 11-51-0) at a rate of 1.0 g per litre of soil should be thoroughly mixed with soil before planting (one level measuring cup of 11-55-0 or 11-51-0 weighs 240g). If soil is very coarse, this rate may be reduced slightly. Great care must be taken to avoid fertilizer concentrations close to the roots or burning and death may result. Fertigation is an alternative method of applying phosphate to the root zone with less risk of root injury. When using fertigation, lower amounts of phosphate can be applied to achieve similar improvements in tree vigour and phosphate nutrition. 6. SOIL AND CHEMICAL TREATMENTS Chemical soil fumigation may be used as a preventative treatment for replant disease. Vapam, Busan, Basamid and Telone C-17 may be used for control of nematodes and soil-borne diseases in orchard soils prior to planting. Telone II and Vydate are registered for control of nematodes only. For more information on fumigation, see the OVTFA publication Soil Fumigation for Orchards: an Overview. March 2006 Return to Tree Fruit Pests and Diseases Return to Pest Management Home