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

Authors: PEARCE, ROBERT - University Of Kentucky; BARLOW, WILLIAM - University Of Kentucky; Pfeufer, Emily

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2022
Publication Date: N/A
Citation: N/A

Interpretive Summary: Pythium species, which are water mold plant pathogens, cause striking levels of disease in commercial tobacco transplant production greenhouses, but their influence on productivity once transplants are moved to the field has never been quantified. Previous fungicide evaluations have been completed that indicated variable efficacy of available products against Pythium root rot (PRR) caused by P. myriotylum, an aggressive tobacco pathogen. In our experiments, we evaluated different fungicides for efficacy against PRR and publish a pictorial scale for growers to evaluate their own transplant crops. Etridiazole and mefenoxam both improved root ball quality (RBQ) as it relates to PRR management. Higher average RBQ improved tobacco transplant establishment, survival, and cured yields when plants were placed in fields without a history of black shank, caused by the most important pathogen of tobacco, Phytophthora nicotianae. At-transplant applications of mefenoxam were positively related to tobacco establishment and survival in fields with a history of black shank, but average RBQ had no relationship to these variables. To further improve the applicability of the RBQ scale, we show that average RBQ> 3.0 results in an average increase of 191 cured kg/ha under typical commercial curing conditions. For the first time, these results quantify the effect of early season PRR management in tobacco transplant production on cured yields and plant productivity. Through the publication of the RBQ pictorial scale, we provide a starting point for commercial tobacco transplant producers to evaluate their crops, in the pursuit of better disease management as well as harvest labor planning. We compare our PRR-influenced productivity measures to other water-intensive production systems, to which our RBQ scale might also be applied.

Technical Abstract: Pythium root rot (PRR) is a significant disease of tobacco transplants produced in the greenhouse floatbed system, but little is quantified about its influence once PRR-infected plants are transplanted in the field. Tobacco producers have limited options to manage PRR, and additional data are needed to reinforce previous efficacy evaluations 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 increased RBQ in tobacco transplants inoculated with Pythium myriotylum. In multi-year, generalized linear mixed model analyses, higher average RBQ from transplants inoculated with P. myriotylum significantly increased plant establishment, survival to season-end, and cured yield in fields without pressure from Phytophthora nicotianae, causal agent of the most important disease in air-cured tobacco production, black shank. Conversely, average RBQ did not significantly influence establishment or survival in fields with extended history of black shank; however, at-transplant application of mefenoxam had positive effects on plant establishment and especially survival irrespective of P. myriotylum influence. To further apply the pictorial scale, a potential threshold of average RBQ > 3.0 improved cured tobacco yield in non-black shank fields by a statistically significant 191 kg/ha. 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.