Cauterising or pruning to minimise spread of cankers caused by Pseudomonas syringae pv. actinidiae in Kiwifruit

Pseudomonas syringae pv. Actinidiae (Psa) causes leaf spotting, cane and leader cankers, or death of kiwifruit vines. Growers require management strategies that minimise the spread of cankers or systemic infection, whilst also minimising canopy loss. This project investigated whether cauterising cankers or pruning beyond the visible canker had any long-term effect in containing progression of the pathogen within the vine. The study included 72 ‘Zesy002’ (commonly known as Gold3) (Actinidia chinensis) vines on one orchard and 87 ‘Hayward’ (A. deliciosa) vines on two orchards, in Te Puke, New Zealand. From one to 30 cane or leader cankers per vine were monitored. Cankers were either left untreated, cauterised using a gas blowtorch, or pruned 40 cm below the lowest symptom. Cankers were delineated initially and canker advance was measured after 1, 3, 7 and 12 months. In ‘Hayward’, pruning proved to be the most effective, and most pruning wounds callused and healed. Cankers spread only where pruning wounds had not callused and healed. Only 11% and 3% of pruned canes on the two orchards, respectively, showed canker advance after 7 months. In comparison, in cauterised and untreated vines the majority (over 80%) of cankers continued to expand, with no obvious difference between these two treatments, and many instances where cankers expanded beyond the 40-cm mark. In Gold3, canker expansion was greater than in ‘Hayward’. Pruning 40 cm below the visible canker margin did not remove the infection from the cane, and cankers continued to expand, in 18.4% of cases. This compares with 27.6 and 27.8% of cankers that expanded beyond the 40-cm mark in the untreated and cauterised vines, respectively, with more than 80% of cankers expanded beyond the original canker margin. The experiments showed that pruning beyond the visible canker reduced the systemic spread of Psa more effectively than cauterising cankers or leaving them untreated