ISHS Acta Horticulturae 800: X International Pear Symposium
ORCHARD MANAGEMENT STRATEGY INFLUENCES LEAF MINERAL ELEMENT CONCENTRATIONS OF D'ANJOU PEAR |
| Authors: | F.J. Peryea, J.E. Dunley |
| Keywords: | Pyrus communis, mineral nutrition, organic, nitrogen, manganese, zinc |
| Abstract:
The Wenatchee Valley of Washington State is the premier winter pear-growing area of the USA. In 2002, fruit growers in the Peshastin Creek subregion of the valley adopted an areawide insect pest management program based on the use of organic insect control tactics. Some of the acreage is managed organically, some conventionally, and the remainder using organic insect pest management practices but conventional horticultural practices (soft IPM orchards). After three growing seasons, reduced fruit yield and sizing appeared as problems in the organic orchards. Many of the trees in the organic orchards showed strong visual symptoms of nitrogen (N) deficiency, including small pale leaves, poor shoot extension, and reddish bark. Leaf mineral analyses in 39 ‘d’Anjou’ pear orchards in 2004–06 showed that the organic and soft trees had consistently lower leaf N and manganese (Mn) concentrations than did the conventionally managed trees. Low leaf N in the organic orchards is associated with weed competition and inadequate N availability from manures and composts. High leaf N and Mn in the conventional orchards is consistent with application of ammonium- and urea-containing fertilizers that supply readily available N and consequent soil acidification due to nitrification of these fertilizers. Low leaf N and low leaf Mn in the soft IPM orchards are anomalous, because these trees receive conventional N fertilizers and herbicides. In contrast to the conventional orchards, the organic and soft IPM orchards rely heavily on horticultural mineral oils and azadirachtin (an organic insecticide derived from parts of the neem tree Azadiracta indica), suggesting that either or both of these products may be causal factor(s) for impaired tree performance. Both are known to injure leaves, reduce transpiration, and cause a reduction in fruit size. | |
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