Study on the sensitivity of Venturia inaequalis to anilinopyrimidine fungicides in Italy

After their introduction in Italy in 1997-1998, anilinopyrimidine fungicides were successfully applied in control of apple scab in pre-bloom. Since 2000-2001 a reduced control of Ventura inaequalis was observed in several Italian apple orchards of Northern Italy where anilinopyrimidines were applied. In this area an in vitro and in vivo study started to evaluate sensitivity to pyrimethanil and cyprodinil of Venturia inaequalis populations and isolates with different origins. In this paper results of in vivo tests with populations, that were more reliable than in vitro assays, are presented. Infected leaves were sampled both in commercial orchards with and without control problems using anilinopyrimidines and in experimental site where these fungicides showed reduced performances; furthermore wild-type populations were considered. The populations were inoculated on apple seedlings grown in glasshouse and treated with pyrimethanil/cyprodinil preventively or curatively (respectively 1-3 days before and 2 days after inoculation). The degree of scab infection on seedlings was estimated 20 days after inoculation. The two fungicides showed very high levels of activity on wild-type populations, both with preventive and curative applications. A moderate reduction of effectiveness was observed in populations collected in commercial orchards without control problems, while those sampled in experimental centre showed the higher activity reductions. The monitoring in commercial orchards, where control failures were observed, presented different sensitivity situations, several of which can be related to reduced performances of anilinopyrimidines in field scab control. The sensitivity reductions were more pronounced with curative applications respect preventive ones.