CORESTA Meeting, Agronomy/Phytopathology, 2023, Cancun, APPOST 02

Mancozeb application in tobacco: a revival of an older chemistry?

North Carolina State University, Department of Crop & Soil Sciences, Raleigh, NC, U.S.A.

In North Carolina, foliar leaf spot diseases, such as Rhizoctonia solani and Alternaria alternata, have increased in severity in recent growing seasons. Historically, azoxystrobin has provided sufficient control of R. solani; however, commercial farmers have reported failures since 2018. Moreover, nothing at present is federally approved for commercial application that would offer suppression of A. alternata. Research was initiated in 2022 to evaluate the efficacy of mancozeb for the suppression of these diseases and to quantify cured leaf dithiocarbamate residues. Across research sites, mancozeb was applied three times (four, six, and eight weeks after transplanting), each at 2.24 kg/ha (1.68 kg ai/ha). A comparison treatment of azoxystrobin was applied at the same intervals with each application delivering 0.58, 0.66, and 0.66 L/ha (0.14, 0.16, and 0.16 kg ai/ha, respectively). Foliar leaf spot pressure was low in 2022 due to above average temperature and below average precipitation. However, in reference to A. alternata, the number of leaf spot lesions was reduced by applications of azoxystrobin and mancozeb in lower stalk leaves at one research site. At the same research site, mancozeb significantly reduced A. alternata severity (3.3 %) relative to the non-treated control (5.4 %). Yield was not affected by treatments. Cured leaf samples obtained from separate evaluations with identical treatment protocols suggest the mancozeb residues are likely to fall below the limit of quantification (1.0 mg/kg) and should not exceed the CORESTA GRL (5.0 mg/kg). Preliminary data suggests that mancozeb could be a useful fungicide to use in rotation with azoxystrobin and that cured leaf residues can be managed with early to mid-season product applications. Additional research will be conducted in 2023 and results will be included in this presentation.