SUCCESSFUL MANAGEMENT OF ORCHARD REPLANT DISEASE IN WASHINGTON

Poor tree growth caused by orchard replant disease is a significant problem on about 80% of replanted apple and pear orchards in north central Washington State. Over the past eight years numerous soil treatments were tested in local orchards in the attempt to improve replanted tree growth and fruit yields. While many substances have little effect, or improved tree growth only during the first or second season after planting, broad spectrum soil fumigants have consistently improved tree growth and yields to commercially acceptable levels. Both methyl bromide, applied at 454 grams per tree site by probe, or broadcast at 450 to 675 Kg/ha, and metam sodium, applied with large volumes of water at 1120 L/ha, have greatly improved long term apple, pear and cherry growth and yields. With both products, when contrasted to unfumigated trees, fruit yields have been increased 200% to 400% during the six or seven years after planting.