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Lateral Clipping of Canopy Influences the Microclimate and Development of Apothecia of Sclerotinia sclerotiorum in Carrots

Four canopy management treatments were evaluated in carrot (Daucus carota) production in Bradford Marsh, Ontario, in 2001 and 2002: (i) unclipped control; (ii) unclipped canopy with manual removal of collapsed senescing leaves at 2-week intervals following the first appearance on the soil; (iii) lateral clipping of the canopy at the initial emergence of apothecia, leaving the debris in the furrow, and (iv) lateral clipping of the canopy with manual removal of the debris from the furrow. Clipping reduced the canopy width by ca. 20% on both sides of the carrot bed by cutting off overlapping leaves above the furrow and senescing foliage on the soil surface. Maximum air and soil temperatures were up to 9.2 and 3.1°C lower, respectively, and relative humidity was up to 30% higher in unclipped canopies than in clipped canopies. The total number of apothecia in clipped plots was reduced by 74 and 76% compared with unclipped plots in 2001 and 2002, respectively. Canopy clipping reduced the quantity of apothecia in the crop by creating an unfavorable microclimate for the development of S. sclerotiorum without affecting the fresh foliar and root weights of carrot at harvest. The presence of clipped foliar debris in the furrow affected the number of apothecia in 2001; however, apothecia under the debris are unlikely to contribute to the overall inoculum in the crop. Lateral clipping also appeared to control Sclerotinia rot of carrot where it occurred (in 2001). This is the first report that documents and quantifies the effects of canopy architecture on the microclimate, development of apothecia of S. sclerotiorum, and Sclerotinia rot in carrot crops.