EFFECT OF NITROGEN FERTILIZATION GREEN PRUNING AND FUNGICIDE TREATMENTS ON BOTRYTIS BUNCH ROT OF GRAPES
A. R’Houma, M. Chérif , A. Boubaker
Grape vineyard culture practices including nitrogen fertilization, removal of leaves, and thinning of clusters, as well as fungicide treatments were evaluated for their effect on the development of Botrytis bunch rot. High nitrogen fertilization predisposed grapevines to infection by Botrytis cinerea and increased disease severity. Latent infection of cups and berries as well as visible infection of clusters increased as the rate of ammonium nitrate amendment increased. Conversely, removal of leaves around clusters, when practiced two or three times during the season, and thinning of berries significantly reduced Botrytis bunch rot development and resulted in less latent and visibly infected clusters and berries. These green pruning practices also attenuated the beneficial effects of nitrogen fertilization on disease development. In vitro experiments revealed that among the tested fungicides, Vinchlozoline, Chlorothalonil, and Dichlofluanide were effective in completely inhibiting the germination of conidia. Iprodione and Procymedone were apparently confronted to the problem of fungal resistance. Folpel, Copper and Chlorothalonil were not able to control mycelial growth as effectively as conidial germination. Field experiments showed that all tested fungicides significantly reduced disease compared to the untreated control, but Methyl-thiophanate, Dichlofluanide and Vinchlozoline provided the best control and gave a more than 60% reduction in infected clusters and approximately 40% increase in yield as compared to the control. Incidence of Botrytis infection was significantly influenced by the period of fungicide application during bloom. The best results are obtained with the fungicide applied early during bloom. Based on these results, a strategy combining cultural management techniques and reasonable use of fungicides is recommended to control Botrytis bunch rot.