244 Effects of Fall Urea and Copper Chelate (CuEDTA) Application on Defoliation, Reserve Nitrogen, and Spring Regrowth of `Fuji' Apple Nursery Trees

Abstract

Bench-grafted `Fuji'/M.26 trees were sprayed with 1% CuEDTA on 31 Oct., defoliated manually on 12 Nov., or allowed to defoliate naturally. Foliar urea at 3% was applied at 14 days and 9 days before CuEDTA treatment. Plants were harvested after natural leaf fall and stored at 2 °C. One set of the plants were destructively sampled for reserve N (expressed as total Kjeldahl N or soluble protein concentration) analysis, and the remaining plants were transplanted into a N-free medium in the spring without any N supply for 40 days after budbreak. CuEDTA resulted in >80% defoliation within 5 days of application. Trees defoliated with CuEDTA had lower reserve N content than naturally defoliated controls, but had higher N than hand-defoliated controls. Foliar urea application before the CuEDTA treatment significantly increased reserve N level in all tree parts, without affecting the efficacy of CuEDTA on defoliation. The extent of spring regrowth was proportional to the reserve N level of the tree. Urea-treated plants, whether hand- or CuEDTA defoliated, had more growth in the spring than hand- or naturally defoliated controls. It is concluded that CuEDTA, as combined with foliar urea, can be used to effectively defoliate apple nursery trees, and increase reserve N level and improve regrowth performance during establishment.