Abstract

The efficacy of reducing fungicide use, by combining chlorothalonil with film-forming antitranspirant products and lengthening intervals between applications, was evaluated for control of blackspot of rose. Antitranspirants included three highly refined pine oil (pinolene) products (Nu Film 17, Vapor Gard, and Wilt Pruf) and two latex products (Stressguard and Transfilm), each of which were applied in combination with chlorothalonil fungicide. Antitranspirant solutions were applied at 2- or 3-week intervals, depending on recommended use of the antitranspirant. Blackspot severity, based on proportion of symptomatic foliage, did not differ among treatments in either year of the study. In both study years, defoliation was lower on plants treated weekly with the fungicide alone, with Stressguard (applied at 0.25% in combination with chlorothalonil every 2 weeks), or with Vapor Gard (applied at 2% in solution with chlorothalonil every 3 weeks) compared to nontreated plants. Overall, the above fungicide and antitranspirant solutions reduced season-long fungicide use by 40-69%, without a decrease in disease control, compared to the weekly chlorothalonil treatment. Plant vigor and/or growth, however, was lower with the antitranspirant treatments compared to chlorothalonil alone.