Possibilities of Applying Soil Herbicides in Fruit Nurseries – Phytotoxicity and Selectivity

Abstract

Fruit-growing is one of the major sub-branches of agriculture in Bulgaria and its development is enhanced by a number of positive prerequisites – favourable soil and climatic conditions, a rich genetic fund of local and introduced cultivars, production experience and national traditions. Production of grafted fruit tree planting material is an important starting point in developing modern fruit-growing. Requirements set by integrated fruit production and the needs of producing certified fruit planting material impose the development of ecologically sound integrated approaches for plant protection, including an efficient control of weed infestation in the fruit nursery, based on selective herbicides without any residual effects, as an element of high agrotechnical practice. In 1991 the European Plant Protection Organization (EPPO) published a scheme for production of certified virus-free fruit trees and rootstocks. The recommendations complying with the scheme of EPPO were included in Directive 92/34 of the Council of the European Economic Community of 28 April 1992 on the marketing of fruit plant propagating materials and fruit plants intended for fruit production. The aim of the Directive was to guarantee the quality of propagating material in the European Union countries after the borders have come down. Certified virus-free fruit planting material could only be produced under the conditions of very high agrotechnical background, including an efficient and ecologically sound control of weed infestation in the fruit nursery. Weed vegetation is a serious problem in fruit crop nurseries. Weeds strongly suppress the growth of rootstocks and grafted trees in the process of planting material production. A direct damage caused by weed infestation is markedly expressed (weed-crop competition for moisture, light and nutrients from soil and introduced with fertilizers). Under the effect of weeds, growth and development of young trees is delayed, wood does not mature and the planting material obtained is non-standard. The indirect damage caused by weeds (dissemination of pests and diseases, including viral ones) in that case is quite strongly expressed, keeping in mind the modern issues to the production of certified, free of viral diseases fruit planting material. In scientific literature there are data that a number of weed species could be also attacked by diseases, including viral ones, and thus weeds become the reason for their spread to the cultivated plants. It was established that PPV (plum pox potty virus) casing the economically most important Sharka disease in stone fruit species, could be hosted by a number of weed species contained in the weed association in the fruit nursery (Oosten, 1971; Rankova & Milusheva, 2001; Milusheva & Rankova, 2002; Milusheva & Rankova, 2006)