Elad, Y., Department of Plant Pathology, ARO, The Volcani Center, Bet Dagan, 50250, Israel

A high percentage of rose flowers collected during winter from greenhouses around Israel developed grey mould disease when incubated in the laboratory in favourable conditions. Symptomless flowers of various cultivars were incubated in a humidity chamber after surface disinfection. More than 50% of the symptomless flowers yielded the pathogen Botrytis cinerea Pers., thus showing the presence of latent infection which probably occurred 3-8 days earlier in the commercial greenhouses. Initially, the symptoms which occurred on affected petals were mainly restricted lesions. However, when flowers were incubated under favourable conditions, necrosis developed and spread. Chemical control of grey mould was tested on cut rose flowers. Partial control of the disease was correlated with reduction in necrosis and a relative increase in restricted lesions (<2 mm in diameter). Of the 18 fungicides which were tested, the following were the most efficient during incubation at 20°C: metomeclan, dichlofluanid, myclozolin, N-phenylcarbamate plus carbendazim (NPC + MBC), polyoxin D, prochloraz and iprodione. When incubated at 10°C, the most effective fungicides against grey mould of rose flowers were NPC + MBC, polyoxin D, chlorothalonil, the detergent Tween 20, and the inhibitor of ethylene activity, silver thiosulphate (STS). Diphenylamine was more effective at 4°C than at 10° or 20°C. STS in combination with each of the fungicides chlorothalonil, polyoxin B, myclozolin or merpan was additively more effective than STS or each of the respective fungicides alone. © 1988.