5.5.28
CHEMICAL CONTROL OF GREY MOULD (BOTRYTIS CINEREA PERS.) IN ORNAMENTAL CROPS

ML GULLINO, G MINUTO and A GARIBALDI

DI.VA.P.R.A. - Patologia vegetate, Universita' di Torino, Via L. Da Vinci 44, 10095 Grugliasco (Torino), Italy

Background and objectives
Grey mould, incited by Botrytis cinerea Pers., causes serious damages on many ornamental crops, in the presence of conditions highly favourable to pathogen development. Its control relies on the adoption of appropriate cultural techniques (such as sanitation to reduce spore inoculum, and relative humidity management, through ventilation and heating) [1] and on the application of fungicides. However, chemical control is complicated by the widespread presence of populations of B. cinerea resistant to benzimidazoles and dicarboximides [2]. Moreover, selectivity must be carefully evaluated before any fungicide is applied on a new cultivar on a large scale.

Materials and methods
During the past few years, the efficacy against B. cinerea of several fungicides, chosen among those already commercially available and some new ones under development, was tested on cyclamen, hydrangea and fuchsia. In all cases, plants were artificially inoculated with the pathogen and kept under conditions very favourable to disease development. Mixed populations of B. cinerea, containing 70 % of sensitive conidia and 30% of conidia with multiple resistance to benzimidazoles and dicarboximides, were used for artificial inoculation, thus simulating a situation often encountered in the practice.

Results and conclusions
In the case of cyclamen, carbendazim + diethofencarb, procymidone + thiram, chlozolinate + thiram, fludioxonil, fludioxonil + cyprodinil and pyrimethanil, applied weekly, for a maximum of 3 sprays/crop provided good grey mould control. Under our experimental conditions, among the tested fungicides, anilazine, chlorothalonil, fluazinam and tebuconazole caused unacceptable flower injury. On hydrangea, grey mould can infect young buds and stems without showing any symptoms, already during summer and fall. During winter greenhouse forcing, B. cinerea attacks flowers and buds, causing very severe damage. Treatments carried out in order to induce phylloptosis and manual defoliation are highly favourable to grey mould, by causing the appearance of many lesions. In the case of such crop, control was based on the application of chemicals under greenhouse in winter, and on field applications. Three chemical sprays showed effective to control grey mould: the first spray was applied in autumn in open field, immediately after phylloptosis, followed by applications during forcing. Carbendazim + diethofencard, procymidone + thiram, benomy] + dichlofluanid, fludioxonil + cyprodinil provided very good disease control. On fuchsia, pyrimethanil and mepanipyrim provided the best disease control, followed by fludioxonil + cyprodinil . Less satisfactory results were obtained by applying procymidone + thiram. The results obtained indicate that the availability of new fungicides, such as those belonging to anilinopyrimidines and phenylpyrroles, with novel modes of action, can improve grey mould control in ornamentals. This is particularly evident when benzimidazole and dicarboximide resistant strains of B. cinerea are quite widespread. However, the easy selection of resistant populations of B. cinerea , coupled with the need of avoiding phytotoxicity as well as the the presence of visible residues on the flowers, strongly suggest to limit the number of chemical applications and to iconsider the use of fungicides within sound IPM strategies.

References
1. Hausbeck MK, Moorman GW, 1996. Plant Disease, 80: 1212 - 1219.
2. Guilino ML, 1992. In: Verhoeff K, Malathrakis NE, Williamson B eds. Recent Advances in Botrytis Research, Pudoc, Wageningen, 217 - 222.