Mr. Tom Auvil (Research Horticulturist, WTFRC) presents a thorough explanation of how to beat apple replant disorders covering everything from economic assessment to cultivar choices and orchard establishment to proper horticultural management.
Mr. Auvil begins his presentation speaking about some of the economic benchmarks that should be used in making decisions about replanting apple orchards. This includes the potential production (bins/acre) and cultivar choice to ensure a high quality product goes to market. He emphasizes the benefit of preplant soil fumigation and the use of genetically resistant rootstocks on replant sites to improve tree establishment and canopy growth. He noted several factors that limit canopy development on replant sites, in particular. These include replant disorders and root rots, mildew, drought stress due to inadequate irrigation (need greater frequency), cropping too heavy too soon and having planting densities that were insufficient. He suggested waiting to crop trees until the third year, irrigating more frequently and planting the trees closer together so that they have less to grow to reach the top trellis wire. He noted that for trees managed for a high degree of vigor, mildew and mites are not typically a problem. He discussed the collaboration of the WTFRC with the USDA-ARS apple rootstock breeding program in Geneva, NY. He noted the superior performance to standard Malling clones in the Geneva rootstocks G.11, G.214, G.41, G.210, G.890 and G.935. He noted that the benefits of fumigation have a limited timeframe while a resistant rootstock provides genetic value for the life of the tree. He emphasized the importance of production system and horticultural practices on tree performance (especially site preparation, water management, tree training and canopy management). Mr. Auvil noted that some scion cultivars vary in their replant sensitivity. In particular, Golden Delicious tends to perform best while Red Delicious performs worst on replant sites. He suggested that the scion/rootstock combination choice is critical. Mr. Auvil discussed the steps in orchard renewal (tree and root removal, deep soil ripping, fumigation). He noted that soil temperature, soil moisture and soil moisture holding capacity at the time of fumigation are critical to a good result. He emphasized using drip or micro sprinkler irrigation for uniform water and nutrient application with more frequent and shorter sets. At planting, he noted that establishing trees with the graft union 4” above the soil line is best to avoid scion rooting. He also noted the importance of providing good soil/root contact through irrigation at planting. He spoke briefly about top working existing orchards to new cultivars and the benefits of training up two leaders and the necessity of staking grafts to reduce the potential for wind damage to the grafts.
Mr. Tom Auvil is a Research Horticulturist with the Washington Tree Fruit Research Commission (WTFRC) based in Wenatchee, WA 98801.