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  • 1 Horticulture and Landscape Architecture, Washington State University, Pullman, WA 99164-6414

Many tree fruit nurseries are limited to fall digging of deciduous nursery stock. Since trees may not defoliate naturally for timely digging, these nurseries may wish to defoliate chemically, which would be less expensive than hand-stripping and may more closely simulate natural leaf abscission. Consequently, test chemicals were applied with hand sprayers at commercial nurseries in central Washington State using single or double applications 1 wk apart. In 1992 on 7 apple cultivars and one pear, 500 ppm NPA + 150 ppm Ethrel significantly enhanced defoliation. Defoliation at 1000 ppm NPA was not superior to that at 500 ppm, and two applications were generally no better than one. However, in 1993, two applications were often more effective than one, and the addition of Ethrel to NPA generally enhanced defoliation if the combination of NPA + Ethrel was applied twice. Alanap and NPA were generally equally effective as defoliants. The addition of Ethrel to Alanap enhanced defoliation in only 3 of 9 cultivars, and then generally only when sprayed twice. Alanap + Ethrel was as effective with Alanap at 300 ppm as with Alanap at 500 ppm Ethrel by itself seldom increased defoliation.

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