McIsaac, G., Sanderson, K. R., Peters, R. D., Garbary, D. J. and Fillmore, S. A. E. 2013. Impact of commercial foliage trimming on disease suppression and yield of processing carrots in Nova Scotia, Canada. Can. J. Plant Sci. 93: 1155-1163. Carrot side-trimming opens the carrot canopy, permitting greater sunlight penetration and airflow. This reduces moisture build-up and creates unfavorable conditions for the development of common carrot pathogens such as Sclerotinia sclerotiorum (Lib.) de Bary. This study was carried out during the 2008 and 2009 growing seasons and was the first to examine the effects of foliage trimming on disease development in the processing carrot production region of Nova Scotia, Canada. Research focused on the effects of foliage trimming on disease suppression and yield using a commercial-sized trimmer in processing slicer carrots over consecutive growing seasons. This study was also the first to look at the effect of trimming on the suppression of Alternaria dauci (J.G. Kühn) J.W. Groves & Skolko and Cercospora carotae (Pass.), two economically important carrot pathogens causing leaf blight diseases in this region of Canada. Plots were established in commercial fields throughout Colchester County, Nova Scotia. Each field had a trimmed and an untrimmed section. All plots were assessed for disease presence at the time of trimming and again at harvest. Foliage trimming was found to have no significant (P=0.05) effect on biological and marketable yield and generated anecdotal reports of ease of crop maintenance and harvest. The severity of diseases caused by Alternaria, Cercospora and Sclerotinia varied among cultivars and significant cultivar×trimming interactions were noted in some cases. Foliage trimming is becoming standard practice in the carrot industry as several commercial carrot producers in North America have adapted the technology to suit their production needs after the prototype foliage trimmer was designed, built, and demonstrated by researchers at Agriculture and Agri-Food Canada, Charlottetown, Prince Edward Island.