Effect of Oxathiin Compounds Spray on the Reducing Oxidant Injury to Tobacco Plants

Abstract

Spray applications of two oxathiin systemic fungicides, carboxin (50% 5, 6-dihydro-2-methyl-1, 4-oxathiin-3-carboxanilide) and oxycarboxin (50% 5, 6-dihydro-2-methyl-1, 4-oxathiin-3-carboxanilide-4, 4-dioxide) were tested to protect flue-cured tobacco from leaf damage induced by air pollution oxidants. Bel W3 (cigar wrapper tobacco) was used for the tests in an ozone exposure chamber, and MC (flue-cured tobacco) for the field tests, respectively. 1. Among the concentrations tested, 1, 000 ppm solution of carboxin and 500 ppm solution of oxycarboxin were most effective in reducing ozone injury. Carboxin higher than 1, 000 ppm however, caused yellowish chlorotic lesions in the young leaves. For escaping from ozone damage the chemicals were most effective on about 5th day after application and not still so effective on the next day of spplication. The effect of sprayed chemicals was found to persist about 10 days. Oxycarboxin sprayed only to lower epidermal surface of a leaf produced same effect as that sprayed to both surfaces. Whereas, the protecting effect by spraying the compound only to upper epidermal surface decreased by approximately half of that by spraying to both surfaces. Those results suggest that the chemicals neither translocate from the sprayed leaves to other nor from one part to the other half beyond the midrib within a leaf. 2. Spray application of oxycarboxin in 1, 500-fold diluted solution (333 ppm) was found to protect field-grown tobacco effectively from oxidant injury. The chemicals was found to produce no damage on treated leaves and no effect was detected on both yield and quality of harvested leaves as well. Carboxin and NF-69 (mixture of oxycarboxin and thiophanate-methyl in the ratio of 1:3.67) delayed leaf maturity remarkably, although oxycarboxin produced no effect in this respect. 3. From the results obtained here, it is indicated that oxycarboxin can be applied as an effective protectant against weather fleck to flue-cured tobacco.