(107) Effects of Defoliants (CuEDTA and ZnSO4) and Foliar Urea on Defoliation and Nitrogen Reserves of Almond Nursery Plants

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  • 1 1Oregon State University, Horticulture, Corvallis, OR, 97331
  • | 2 2USDA–ARS, Horticultural Crops Research Unit, Corvallis, OR, 97330

One-year-old field-grown `Nonpareil'/'Nemaguard' and `Nonpareil'/`Lovell' almond nursery trees were used to study the effects of chemical defoliants (CuEDTA and ZnSO4) and foliar applications of urea on defoliation and nitrogen (N) reserves. Although both chemical defoliants significantly promoted earlier defoliation, CuEDTA was more effective than ZnSO4 in promoting early defoliation. Two applications of defoliant had a similar effect as one application on promoting leaf abscission. Foliar applications of urea in addition to defoliant applications (urea + defoliant treatments) generally increased the efficiency of ZnSO4 (1.25% to 2%) and CuEDTA (0.5%) in promoting early defoliation. Although treatments with only defoliants did not consistently lower N reserve levels, trees treated with foliar urea or urea + defoliants had significantly higher nitrogen reserves compared to trees receiving only defoliant treatments. N reserves were comparable in urea + defoliant-treated trees to the levels found in naturally defoliated (control) trees. We conclude that both CuEDTA and ZnSO4 are effective in promoting early defoliation of almond nursery trees. Combining urea with defoliants can effectively promote early defoliation and is important for achieving N reserves similar to naturally defoliated trees.

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