Management of Pythium myriotylum in Tobacco Transplant Production Greenhouses

Abstract

Pythium root rot is a common disease that can threaten tobacco seedling production in greenhouses. However, management tools are limited in tobacco transplant production greenhouses. To identify additional Pythium control options, oomyceticide treatments (ethaboxam, mefenoxam, and copper ethanolamine complex) and nonoomyceticide (ultraviolet light and copper ion) water treatments were compared with etridiazole and an untreated control on TN 90LC tobacco seedlings inoculated with Pythium myriotylum in greenhouses. All the treatments in oomyceticide trials were applied to the bay water once before inoculation, when seedling roots had extended into the water. The inoculum was applied immediately before seeding in nonoomyceticide trials, in which etridiazole was applied to bay water once, 2 weeks after seeding, as a positive control. Nonoomyceticide treatments were applied three times: 24 h before, 2 weeks after, and 4 weeks after seeding. At the end of the tobacco transplant production season, ethaboxam and mefenoxam significantly (P < 0.05) reduced root rot incidence and severity by as much as 100%, compared with the untreated control. Ethaboxam and mefenoxam also significantly (P < 0.05) reduced oospores produced in infected root tissues while significantly (P < 0.05) increasing root length and weight. Ultraviolet radiation and copper ion treatments had no significant effects on tobacco seedling root length or weight compared with the untreated control, although the copper ion treatments significantly (P < 0.05) reduced root rot severity and oospores produced in root tissues. Similar to etridiazole, ethaboxam and mefenoxam consistently reduced the area under the disease progress curve (AUDPC) of Pythium root rot, but copper ion treatments only reduced AUDPC significantly (P < 0.05) in one trial.