Efficacy of fungicides and a systemic acquired resistance activator (acibenzolar- S-methyl) against tobacco blue mould

Abstract

Tobacco blue mould, caused by Peronospora tabacina Adam ( Peronospora hyoscyami f. sp. tabacina Skalicky 1964) can be an economically devastating leaf spot disease in shade and broadleaf cigar wrapper tobacco ( Nicotiana tabacum L.) types grown in Connecticut and Massachusetts. We investigated the effects of dimethomorph plus mancozeb and azoxystrobin fungicides as well as acibenzolar- S-methyl, a systemic acquired resistance inducer, on disease severity over 2 years in both shade-grown and broadleaf tobaccos. All fungicide and fungicide plus acibenzolar- S-methyl treatments applied were effective in reducing the number of blue mould lesions per plant. Treatments containing acibenzolar- S-methyl were the most effective, resulting in almost complete control. Substituting two or three applications of acibenzolar- S-methyl at label rates for dimethomorph plus mancozeb treatments in a spray program increased blue mould control over the same number of dimethomorph plus mancozeb applications by 28–94 percent. The effects of acibenzolar- S-methyl application on cured leaf quality were determined in commercial shade tobacco fields in 2000 and 2001. Leaves were cured, processed and commercially evaluated for quality in a blind test. Standard fungicide applications of dimethomorph plus mancozeb applied on a 14-d interval were compared to three acibenzolar- S-methyl treatments. Economic value was not different between treatments in 2000, but acibenzolar- S-methyl applied at 10-d intervals was associated with reduced value in 2001 when plants were more subject to drought and heat stress.