Actigard Increases Fungicide Efficacy Against Tobacco Blue Mold

Blue mold, caused by Peronospora tabacina, can be economically damaging to cigar wrapper tobacco (Nicotiana tabacum). We evaluated acibenzolar-S-methyl (ASM) as Actigard 50WG alone and in combination with a standard fungicide program for efficacy against blue mold on shade-grown cigar wrapper tobacco in Windsor, CT. The standard fungicide program consisted of dimethomorph (Acrobat MZ or Forum) plus mancozeb (Dithane), alternated with azoxystrobin (Quadris), and applied at label rates on six occasions at 14-day intervals. Treated and untreated 5-by-5-m plots were replicated four times in 2003, 2004, 2005, 2006, and 2007. ASM treatments were applied alone or in combination with fungicides at the third, fourth, and fifth spray dates at rates ranging from 1.1 to 17.5 g a.i./ha. Disease was greatest in nontreated plots and reduced in all fungicide, Actigard, or combination treatments. The combination of three ASM applications at rates of 17.5 g a.i./ha down to 4.4 g a.i./ha with the standard fungicide program was more efficacious than either fungicides or ASM alone (P < 0.001) in reducing the number of blue mold lesions per plot or number of diseased leaves harvested. The combination of fungicides and low rates of ASM (2.2 or 1.1 g a.i./ha) was similar to either fungicides or ASM (17.5 g a.i./ha) applied alone. Combining low rates of ASM with fungicide applications greatly increased efficacy and marketable yield.