Alternaria leaf blotch and fruit spots on apples, caused by the fungus Alternaria alternata f. sp. mali is a serious disease of apples in many countries, including Israel, where severe outbreaks of Alternaria fruit spots have recently been observed on cv. Pink Lady.
The disease can affect apple cultivars such as Golden Delicious, Starking Delicious, Indo, Gala, and Pink Lady. Leaf infection may cause 60–85% defoliation in susceptible cultivars, while fruit symptoms are usually limited to small, dark, corky lesions, often associated with the lenticels. The pathogen may cause soft rot, particularly when the skin was wounded by mechanical damage or insects, or there are cracks around the fruit calyx.
Scientists at University of Haifa (Israel) have found that the disease may be successfully controlled by application of fungicidal mixtures to the fruit at the proper phenological development stage.
"Ortiva-Top (azoxystrobin+difenoconazole) and Azimut (azoxystrobin+tebuconazole) resulted effective in inhibiting 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. - The scientists explain - In seven field trials Ortiva-Top and Orpan (tebuconazole +captan) resulted the most effective, and reduced calyx and fruit body rot by 60–88 and 58–92%, respectively, compared with untreated trees".
Scientists conclude that a new spray program can be adopted, in which only four to six sprays of Ortiva-Top, Orpan or Azimut are used, starting at about 115 days after petal fall. This program can effectively control Alternaria fruit rot in Pink Lady apples in Israel.
Source: Lior Gur, Moshe Reuveni, Yigal Cohen, 'Control of Alternaria fruit rot in 'Pink Lady' apples by fungicidal mixtures', 2020, Crop Protection, Volume 127.