Control of Alternaria fruit rot in 'Pink Lady' apples by fungicidal mixtures

Fruit body rot and calyx rot caused by Alternaria alternata f.sp. mali recently appeared in Israel as a severe disease of apple, cv. Pink Lady. No such heavy rots of fruits were reported elsewhere, nor are there any known control measures against the disease. We found that the disease may be successfully controlled by application of fungicidal mixtures to the fruit at the proper phenological development stage. Ortiva-Top (azox-ystrobin+difenoconazole) and Azimut (azoxystrobin+tebuconazole) effectively inhibited spore germination, mycelial growth, and rot development in detached fruits. Mixtures of Azimut or Ortiva-Top with Captan were synergistically effective in controlling the disease in detached fruits. In seven field trials Ortiva-Top and Orpan (tebuconazole+captan) were the most effective, and reduced calyx and fruit body rot by 60-88 and 58-92%, respectively, compared with untreated trees. Based on these findings a new spray program was adopted, in which only four to six sprays of Ortiva-Top, Orpan or Azimut were employed, starting at about 115 days after petal fall; it effectively controlled Alternaria fruit rot in 'Pink Lady' apples in Israel.