Controlled studies further the development of practical guidelines to manage dodder (Cuscuta gronovii) in cranberry production with short-term flooding

Flooding is an inexpensive cultural practice used for pest management in Massachusetts cranberry (Vaccinium macrocarponAit.) production. This project examined the use of short-term floods (<72 h) for dodder (Cuscuta gronoviiWilld.) management under controlled conditions. Using incubators, seed was submerged in water for 0, 24 and 48 h at 10, 15 and 20°C (simulating spring water temperatures) and 0, 12, 24, 36 and 48 h at 15, 20 and 25°C (simulating summer water temperatures). Two 1-year controlled studies (field and greenhouse) evaluated three flood durations (0, 24 and 48 h) and four flood initiations (1, 2, 3 and 4 weeks after early seedling emergence (AEE)). Treated seeds were planted to cranberry vines and to Petri dishes; percent germination, degree of dodder attachment and dodder biomass data were collected. Treatments had limited effect on seed germination. Flooding 4 weeks AEE resulted in the lowest mean attachment ratings and dodder stem biomass on cranberry. This preliminary work provides evidence that flooding may retard dodder stem growth rather than reducing seed germination and that floods initiated after some time has elapsed after early emergence may be more effective than those initiated closer to the time of seedling emergence. More information is needed to thoroughly understand the processes involved; however, small projects such as this can provide interim guidelines that growers can immediately consider when deciding on a dodder management program.

Swamp Dodder (Cuscuta gronovii) Management in Carrot Production

Field research was conducted to evaluate the effectiveness of herbicides and carrot mowing for swamp dodder control. Herbicide evaluation indicated the highest carrot yield and lowest crop injury with pendimethalin compared to the industry standard linuron. Swamp dodder control with pendimethalin was greater than 80% at 56 and 70 d after planting (DAP). Other herbicides controlled swamp dodder, but crop injury was unacceptable. Carrot yield was greater where pendimethalin ors-metolachlor was applied compared to all other herbicides. Carrot mowing once 72, 86, or 100 DAP and mowing twice (72 plus 100 DAP) reduced the percentage of carrots infected with swamp dodder. Carrot infection level was least when mowed 100 DAP, and mowing did not increase yield compared to the non-treated check. These results suggest that the integration of pendimethalin for early-season swamp dodder control, followed by mowing 100 DAP, could reduce the impact of swamp dodder on carrots.

Swamp Dodder (Cuscuta gronovii) Applied Ecology in Carrot Production

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.