Post harvest control of Phytophthora cryptogea of witloof chicory with different fungicides and possible occurrence of resistant strains

Mefenoxam applied on chicory roots at 4.8 g active ingredient 100 l−1 achieved a very effective control of Phytophthora cryptogea, one of the main pathogens of witloof chicory. In seven trials, less than 10% of the roots treated with mefenoxam showed necrosis. The mefenoxam efficacy was better than that of propamocarb-HCl at 180 g 100 l−1 (89-100% of infected roots) or mancozeb at 300 g 100 l−1 (97-100% of infected roots). The efficacy of fosetyl-Al appeared to be irregular (2-98% of infected roots). Sensitivity to mefenoxam and azoxystrobin of some P.cryptogea strains was studied on amended media. Among the six strains tested, one was resistant to mefenoxam and two were moderately sensitive to azoxystrobin. The risk of occurrence of resistant strains in practice has to be considered; management of resistance to the two fungicides by application scheduling is proposed.