A POSSIBILITY FOR THE CONTROL OF BACTERIAL BLAST, PSEUDOMONAS SYRINGAE, ON APRICOTS
Bacterial blast, caused by Pseudomonas syringae, has been a problem on apricots growing in Central Otago for more than fifty years. The disease affects tree health and fruit finish. A copper-based programme was developed to control bacterial blast in the 1950s and has generally been retained, with some extension into spring. However, there is now considerable environmental pressure to replace copper. Recent trials in Central Otago compared a single application of sulphur or copper applied to three blocks of apricot cv. Sundrop at the late dormant stage. On two orchards, four rows of mature apricots cv. Sundrop were treated with an airblast sprayer applying 124 g ai copper/100 litres (copper oxide) and another four rows with 140 g ai sulphur/100 litres as Kumulus® on 19 August 2004. On a third orchard, an airblast sprayer applied 61 g ai copper/100 litres (copper hydroxide) or 160 g ai/100 litres sulphur (Kumulus®) to fifty Sundrop apricot trees on 16 August 2004 in a split block design. The proportion of fruit from the sulphur- and copper-treated trees showing bacterial symptoms was assessed at harvest (n = 500-2000 fruit). The trees that had received the sulphur programme in the first two orchards produced half as many fruit with bacterial blast symptoms as those that received the copper programme. There was no significant difference between the treatments in the third orchard (P<0.05), where the level of infected fruit was high (25 and 26%). The bacteria responsible for the spotting on the fruit were identified as Pseudomonas syringae at each site. Investigations are continuing into the effect of sulphur on fruit finish and yield, together with its long-term effect on tree health. The use of sulphur on apricots is currently not recommended in New Zealand.
McLaren, G.F. (2006). A POSSIBILITY FOR THE CONTROL OF BACTERIAL BLAST, PSEUDOMONAS SYRINGAE, ON APRICOTS. Acta Hortic. 717, 111-114
apricot fruit, sulphur, copper