Erfolgreiche Bekämpfung des Apfelschorfs mit Kalziumhydroxid

Summary

In an attempt to control scab, a 12-year-old apple orchard was treated with suspensions of 5 g/l hydrated lime (Ca(OH)2) using overhead irrigation for 15 min. No other fungicides were used. In treatment A, irrigation was started when infection according to Mills had taken place. In treatments B and C, treatment was delayed by 6 h and 20 h, respectively. Irrigation was initiated when the scab warning system signaled even very low infection risk, and a total of 62 treatments were applied. At harvest, the fruits of ‘Golden Delicious’ and ‘Jonagold’ varieties of untreated controls were scabbed, while those of ‘Elstar’, ‘Fiesta’, and ‘Kent’ had no visible scab symptoms. During both conventional and ULO storage for 7.5 months, all control fruits developed scab symptoms. All fruits from A, B, and C treatments were free of scab at harvest and after storage. All control trees had scabbed leaves at harvest time; treated trees were free of scab on their upper leaf surfaces, while up to 15% of the leaves had at least one scab lesion on their lower surfaces. This was attributed to poor wetting of these surfaces by sprinkler irrigation, while the fruits and upper leaf surfaces were fully covered with hydrated lime suspensions. At harvest, leaves and fruits were covered with whitish calcium carbonate residues which could be removed by a brief dip in 20 g/l aqueous citric acid. There were no signs of phytotoxicity on either leaves or fruits.