Measuring the impact of crop management on crop diseases, weeds and insect pestsat the regional scale

Abstract: Organic farming still represents a small part of agricultural land in France but isdeveloping fast due to government incentives and a growing demand. However, it is unknownwhether it would favour or reduce pests and diseases at the landscape scale. Our objective was tomeasure effects of crop management in a given field and neighbouring fields on pests’ dynamics,through surveys of farmers’ fields in a small region. The cropping practices presented a certaindegree of diversity but a hierarchical classification of the fields gave no indication of strongdifferences between different types of cropping systems, except the obvious separation betweenorganic and conventional farming. Wheat fields were classified according to their management(organic vs. conventional) and management of neighbouring fields (at least one organic vs. allconventional). Leaf blotch was significantly higher in conventional fields, but there was no effectof crop management in the adjacent fields. For powdery mildew, the high variability betweenplots led to non-significant effects. The organic plots harboured significantly more weeds withhigher diversity than conventional plots. The effect on weeds of having at least one organic plotin the neighbourhood was inconsistent between observation dates. Significantly fewer aphidsoccurred in the organic plots than in the conventional plots, and having at least one organic plot inthe neighbourhood significantly decreased the number of aphids.