ISHS Acta Horticulturae 705: V International Walnut Symposium
WALNUT BLIGHT-APICAL NECROSIS: TEST OF AGRONOMIC CONTROL |
| Author: | G. Bouvet |
| Keywords: | apical necrosis, walnut blight, walnut, nutrition, soil, crop management, Xanthomonas campestris pv. juglandis |
| Abstract:
Walnut blight and apical necrosis are majors problems in walnut orchard in the south east of France. In case of severe attacks, fifty to eighty percent of the harvest can be lost. Two types of symptoms are known: lateral attacks due to walnut blight and apical attacks, which are deep and probably linked to nutrition problems, even if bacteria are present on this type of symptom. In certain situations, treatments with copper, the only active matter, are inefficient against apical necrosis even if massive resistance to copper are not proved. Thus, risk of resistance to exists. In a recent past, assays with oligo elements or foliar fertilizer showed relative disappointed results. We know that walnut blight and also apical necrosis are more spread on zones with problems of soil (low pH, light soil, stony soil, low level of organic matter) or and of crop management (high density of tree, severe cut off). An assay composed of three orchards began in 2003. The purpose is to test a change of crop management on a half of three orchards. The aim is to control the nutrition of the trees, particularly for nitrogen, in order to decrease the impact of stress due to variation of nutrition, so that the tree will be less sensible to apical necrosis. The new management tested is based on: - reduction of grass mowing to control the mineralization, and to report this mineralization after bloom period, - irrigation by sprinkler instead of drop by drop to mobilize the whole root system, - limitation of the crop cutting to control the growth, - splitting up nitrogen fertilization into three parts and - annual spread of calcium and organic matter to improve properties of the soil. We must wait three to five years to expect obtaining the first results. This global approach of this disease is the base of crop integrated management and is a way which doesn't have been tested. The objective is not to eradicate apical necrosis on this difficult type of soil but to keep lost due to apical necrosis bearable. | |
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