Management of Pythium myriotylum in burley tobacco transplants and its effect on field productivity

Pythium root rot (PRR) is a significant disease of tobacco transplants produced in the greenhouse floatbed system, but little is known about its influence once PRR-infected plants are transplanted in the field. Tobacco producers have limited chemical options to manage PRR, and additional data are needed on the efficacy of the fungicide active ingredients etridiazole, mefenoxam, and hydrogen peroxide-peroxyacetic acid. With the support of a pictorial, ordinal root ball quality (RBQ) rating scale, etridiazole and mefenoxam improved RBQ in tobacco transplants inoculated with Pythium myriotylum in greenhouse trials. In multi-year, generalized linear mixed model analyses, higher average RBQ in transplants significantly increased plant establishment, survival to season-end, and cured yield in research farm trials. To further apply the pictorial scale, a potential threshold of average RBQ >3.0 would be expected to result in 201 kg/ha more cured yield, over transplants with average RBQ ≤3.0. These results document for the first time the influence of transplant PRR on cured tobacco yield, in addition to its interim effects on tobacco establishment and survival. While additional data are needed to support a critical RBQ value, estimated effects of transplant quality on cured tobacco yield may assist growers in post-transplant farm management decisions, such as labor planning.