ANALYSIS OF CROP LOSS IN THE MULTIPLE PATHOSYSTEM GROUNDNUT RUST LATE LEAF-SPOT .2. STUDY OF THE INTERACTIONS BETWEEN DISEASES AND CROP INTENSIFICATION IN FACTORIAL-EXPERIMENTS

Two factorial experiments were conducted to study the relationships between the intensification of the groundnut crop and the injuries of foliar diseases, in their effect on damage. In a first experiment, the overall damage caused by spontaneous levels of rust, early leaf spot and late leaf spot increased with intensification, represented by four successive levels. In a second experiment, the interactions between two input factors (cultivar potential yield and weed control) and manipulated levels of rust and late leaf spot were studied, using a double strip-plot design. Significant interactions were found, indicating a less than additive interaction between rust and late leaf spot injury on damage, and an increase of damage due to rust simultaneously with increasing cultivar potential yield and weed control. Cross-sectional and longitudinal analyses were conducted to check the effects of treatments on foliar growth and defoliation and to check the effects of disease treatments on epidemics. The results of analysis of variance were compared with the results of multiple regression analyses. The two experiments demonstrate that the damage due to varying injury levels of rust and leaf spot depends on the intensification level, that is, the production situation.