Efficacy of different chemical and biological products in the control of Pseudomonas syringae pv. actinidiae on kiwifruit

The recent outbreak of bacterial canker on kiwifruit, caused by Pseudomonas syringae pv. actinidiae, has caused considerable damage to the international kiwifruit industry. Commercial products, and products under development, were evaluated over 2 years to assess their ability to control bacterial canker on kiwifruit under controlled conditions. The results were compared with two trials carried out in a kiwifruit orchard located in northern Italy during 2011 and 2012, to test the preventative efficacy of different copper formulations against P. syringae pv. actinidiae. In the greenhouse and orchard trials, copper hydroxide and the mixtures of copper hydroxide and copper oxychloride, significantly reduced the foliar symptoms by 70-80 % compared with the control, and showed low phytotoxicity. Similar efficacy was provided by acibenzolar-S-methyl, whose use has been temporarily extended to kiwifruit in Italy, with a maximum of four treatments per year. However, the product showed phytotoxicity on one-year old plants. The efficacy of fosetyl-Al was lower, particularly in the first orchard trials of 2012 and 2013. The efficacy of the other products tested never exceeded 30-40 %, and some products were not significantly different from the control. Kiwifruit plants grown in a steamed peat substrate mixed with compost obtained from digested organic matrices of municipal solid waste showed significantly fewer leaf spots compared with untreated controls. Copper compounds alternated with resistance inducers could be used in combination with compost, in order to develop new integrated control strategies to reduce the disease development and spread.