Swamp dodder continues to spread through Wisconsin carrots, reducing crop yield and quality. Greenhouse research was conducted to evaluate the effect of swamp dodder infection timing on carrot development and to evaluate carrot cultivar tolerance to the parasite. Data collection included measurement of carrot processing qualities such as root length, root diameter, and fresh weight, as well as quantification of carrot leaf biomass and swamp dodder biomass. Carrot processing qualities were reduced the most in carrots infected 14 d after emergence (DAE). Carrots infected 70 DAE were similar to the noninfected carrots for all processing qualities. Carrot cultivars differed in tolerance of swamp dodder parasitism. All parameters for cultivar tolerance were significantly reduced by swamp dodder infection; however, ‘Enterprise’, ‘Sweet Bites’, ‘Sugar Snax 54’, ‘Topcut 93’, and ‘Mokum’ were most tolerant of parasitism and exhibited minimal reductions in root length, diameter, and fresh weight compared with other cultivars. ‘7626B’, ‘Bolero’, ‘Legend’, and ‘Imperial Cuts’ cultivars grew poorly when parasitized.

Nomenclature: Swamp dodder, Cuscuta gronovii; carrot, Daucus carota L