Influence of Essential Oils on Post-infection Botrytis Damage in Cut Roses1

Abstract

Abstract We assessed the degree to which 16 post-infection treatments controlled Botrytis (Botrytis cinerea Pers. ex. Fr.) damage in cut roses (Rosa × hybrida). Additional experiments examined whether essential oils (EO) of cinnamon (Cinnamomum zeylanicum Blume) leaf (CLO), clove (Eugenia caryophyllata Thunb.) bud (CBO), and thyme (Thymus vulgaris L.) (TO) could reduce damage in Botrytis-infected cut roses. The 16 treatments applied to ‘Light Orlando' cut roses differed in reducing Botrytis damage and causing phytotoxicity damage. Only the synthetic fungicide fludioxonil [applied as 0.23 g · L−1 (0.00024 oz · fl oz−1) Medallion®] resulted in the desirable combination of greatly reduced stem termination frequency due to Botrytis damage and relatively minor flower phytotoxicity. When applied to cut rose ‘Freedom' or cultivars with light colored flowers (‘Cool Water', ‘Jessika', ‘Polar Star', ‘Tiffany'), all EO aqueous solutions caused pronounced phytotoxicity damage, but only TO reduced Botrytis damage significantly compared to untreated flowers. Roses exposed to EO vapor rather than an aqueous solution tended to exhibit less phytotoxicity. Vapors of CLO and CBO tended to reduce Botrytis damage less and caused greater flower phytotoxicity than TO vapor and aqueous fludioxonil. Thyme oil vapor exposures of 4.6 and 9.1 ppm warrant further investigation. Index words: Botrytis blight, Botrytis cinerea Pers. ex. Fr., cut flowers, floriculture, fungicide, gray mold, Rosa × hybrida. Chemicals used in this study: Bacillus subtilis (Cease®), bleach (Clorox®), chlorothalonil (Daconil®), copper sulphate (Phyton® 27), fenhexamide (Elevate®), fludioxonil (Medallion®), hydrogen peroxide (ZeroTol® 2.0), iprodione (Chipco® 26019 Flo), potassium bicarbonate (Milstop®), pyraclostrobin + boscalid (Pageant® Intrinsic®). Species used in this study: Rose (Rosa × hybrida) ‘Cool Water', ‘Freedom', ‘Jessika', ‘Polar Star', ‘Tiffany', Botrytis (Botrytis cinerea Pers. ex. Fr.).