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  In-Furrow Applications of Metalaxyl and Phosphite for Control of Pink Rot (Phytophthora erythroseptica) of Potato in New Brunswick, Canada

Khalil I. Al-Mughrabi1, Rick D. Peters2, H.W. (Bud) Platt2, Gilles Moreau3, Appanna Vikram1, René Poirier1 and Ian MacDonald2

Partner: Potatoes New Brunswick

Abstract: The efficacy of metalaxyl-m (Ridomil® Gold 480EC) and phosphite (PhostrolT) applied at planting in-furrow against pink rot (Phytophthora erythroseptica Pethyb.) of potato (Solanum tuberosum L.) 'Shepody' and 'Russet Burbank' was evaluated in field trials conducted in 2005 and 2006 in Florenceville, New Brunswick, Canada. Inoculum made from a metalaxyl-m-sensitive isolate of P. erythroseptica from New Brunswick was applied either in-furrow as a vermiculite slurry at planting or as a zoospore drench in soils adjacent to potato plants in late August. After harvest, the number and weight of tubers showing pink rot symptoms were assessed and expressed as percentages of the total tuber number and total weight of tubers. Metalaxyl-m applied in-furrow was significantly (P<0.001) more effective against pink rot than phosphite. The mean percentage of diseased tubers as a percentage of total tuber weight was 1.53% (2005) and 1.152% (2006) for metalaxyl-m-treated plots and 9.556% (2005) and 2.82% (2006) for phosphite-treated plots, a percentage similar to that obtained in inoculated control plots with no fungicide treatment. The mean percentage of diseased tubers expressed as a percentage of the total number of tubers was 1.71% (2005) and 1.32% (2006) for metalaxyl-m-treated plots and 10.14% (2005) and 3.13% (2006) for phosphite-treated plots. Disease incidence was significantly higher (P<0.001) using the late-season inoculation technique (respective means in 2005 and 2006 were 9.98% and 3.78% diseased tubers, by weight, and 10.556% and 3.889%, by number) than with the in-furrow inoculation method (respective means in 2005 and 2006 were 3.32% and 0.71% by weight, and 3.71% and 1.273%, by number). The potato cultivar 'Shepody' was significantly (P<0.001) more susceptible to pink rot (9.879% and 3.32% diseased tubers, by weight, in 2005 and 2006, respectively and 10.56% and 3.96%, by number) than 'Russet Burbank' (respective means in 2005 and 2006 were 3.43% and 1.172%, by weight, and 3.70% and 1.182%, by number). Our findings indicate that , unlike phosphite, metalaxyl applied in-furrow at planting is a viable option for control of pink rot caused by metalaxyl-sensitive strains of P. erythroseptica, while phosphite was ineffective.

1Potato Development Centre, New Brunswick Department of Agriculture and Aquaculture, 39 Barker Lane, Wicklow, NB E7L 3S4, Canada
2Agriculture and Agri-Food Canada, 440 University Avenue, Charlottetown, PEI C1A 4N6, Canada
3McCain Foods (Canada), Grand Falls, NB E3Z 3E3, Canada.

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