Maryblyt 4.2: Prediction of fire blight outbreaks in Italy (Po valley)

A project (1993-1996) is under way to assess infection risks by analyzing the phenological-climatological data using the MARYBLYT model and monitoring Erwinia amylovora in asymptomatic pear, apple and hawthorn flowers collected in different Veneto and Emilia-Romagna fruit-growing areas. Analyses of bulk samples of intact open flowers with brown anthers were all negative and conventional and molecular methods did not reveal E. amylovora in any of the suspect bacterial isolates. In Veneto, data for MARYBLYT processing were collected from a "Conference" pear orchard. In 1993 the model revealed high risk conditions in the last week of bloom and in the post-bloom period with 3 and 1 infection cycles of blossom blight symptom (BBS) and shoot blight symptom (SBS). No secondary bloom was recorded. In 1994, BBS were hindered by low temperatures during bloom; delay in SBS was due to the absence of blossom infections. The model predicted trauma blight symptoms (TBS) caused by hail at the end of August but not BBS on secondary blossoms in October. In 1995 no BBS were forecasted during primary bloom. In Emilia-Romagna, the model was assessed in 1994-95 in 2 and 4 stations. The risk index in 1994 was medium-low with no BBS on "Williams" and "Conference" pears or "Golden" apples. Four infections during secondary bloom (April-May) were only predicted in one station. In 1995 the weather was very conducive to BBS during secondary bloom due to higher temperatures and abundant rain. MARYBLYT seemed to provide an accurate prediction of infection periods and/or symptom development.