HEAT-TREATMENT FOR THE CONTROL OF ROSE AND CARNATION GRAY MOLD (BOTRYTIS-CINEREA)

Thermal dip treatment for flower heads was found effective against grey mould of roses. Dipping of flowers in tap-water at 50-degrees-C for 20-40 s was more effective than at higher or lower temperatures and than for longer treatments. The treatment was effective in five out of six rose cultivars and in one carnation cultivar. A 60% reduction in disease severity following the treatment was observed in flowers naturally infected by Botrytis cinerea, whereas the treatment was not effective against artificial infection of flowers. Conditioning of flowers for 2 days at 10-degrees-C and high relative humidity before incubation under grey-mould-conducive conditions (15-degrees-C, high humidity) increased the efficacy of the thermal treatment. Moreover, the combination of heat with 3 mM catechol was additively more efficient in reducing grey mould. The surfactant Tween 20 (0.01%) improved the effect of treatment at 45-degrees-C for 20 s. A combination of heat with the fungicide chlorothalonil did not improve effectiveness, whereas when polyoxin B was combined with heat it was better than either treatment alone. The temperature of petals at the edge and centre of flower reached 37 and 27-degrees-C, respectively, at the end of a 20-s incubation period in 50-degrees-C water. Conidia treated at 34-40-degrees-C for 10-20 s incited 60% less severe disease than conidia treated at 25-degrees-C in water.