Effect of plant architecture on microclimate, white mold and yield of dry beans (Phaseolus vulgaris L.) and implications for disease management

White mold, caused by Sclerotinia sclerotiorum Lib. deBary is a serious yield-limiting disease of dry edible beans. Many cultivars/lines that avoid white mold due to upright and open plant architecture do not yield as well as the standard cultivars in the absence of disease but yield better in the presence of disease. Plant architecture influences the microclimate of dry bean plants causing favorable conditions for white mold infections in dense canopies. Experiments consisting of cultivars/lines and near-isolines of dry beans with different plant architectures were conducted in 1990 and 1991 to evaluate white mold and yield under unprotected and protected treatments in a white mold nursery. In a parallel study the microclimate of Great Northern (GN) \u27Starlight\u27 (semi-upright and open canopy) and GN \u27Tara\u27 (prostrate and dense canopy) dry bean cultivars were studied in relation to white mold. Leaf wetness was predicted for canopies of both cultivars. Severe white mold infection developed in the plots in 1990 and a moderate level of infection developed in 1991. Three principal factors (canopy, porosity, and height) were identified by factor analysis. The linear regression of these factors on white mold was 0.56 (cultivars/lines, 1991), 0.58 (near-isolines, 1990), and 0.50 (near-isolines, 1991). Low association (0.08) was found for these factors in 1990 under severe white mold. Diffused non-intercepted radiation and fractal dimension over the furrow and between the rows can be used as a measure of porosity to select lines with avoidance to white mold in the absence of disease. GN \u27Starlight\u27 had shorter dew duration, later onset of dew, earlier drying of dew, higher daytime air and soil temperatures, and lower dew point temperature in comparison to GN \u27Tara\u27. Leaf wetness predictions were fairly accurate for the open canopy of GN \u27Starlight\u27 during day (92%) and nighttime (89%) conditions