Managing Pythium root rot in tobacco float beds with a non-ionic surfactant
Pythium root rot (PRR) is a serious disease of tobacco transplants produced in float beds, a hydroponic system common in the southeastern U.S. Current control measures are sanitation and the preventive use of etridiazole (ETDZ); however, sanitary practices are not effectively employed and ETDZ is costly and relatively phytotoxic. In 2008 and 2009, the number and timing of applications of Naiad, a non-ionic surfactant known to suppress Oomycetes, needed to provide control of PRR equivalent to ETDZ were evaluated in Kentucky and Virginia. Preventive treatments included Naiad (1000 ppm) applied once at seeding, 3 weeks after seeding (WAS), or 5 WAS. Two- and three-application treatments consisted of combinations of the aforementioned single applications. ETDZ was applied at 0.07 ml per L of float water at 3 and 5 WAS. All trays were inoculated with Pythium 1 day after the 3 WAS applications of ETDZ. Naiad also was applied after symptoms of PRR were first observed (FS); ETDZ was applied at FS at 0.1 ml per L of float water. Naiad applied at 3 and 5 WAS, or at S, 3, and 5 WAS, was comparable to ETDZ against PRR when applied preventively or curatively, and a similar number of useable transplants were obtained. Applications of Naiad after FS did not differ from the untreated control in terms of disease severity or numbers of useable seedlings. Naiad appears to be a suitable alternative to ETDZ for management of PRR when applied preventively. Additional work is needed to evaluate plant safety and compatibility with ETDZ in a control program.