Disclosed is a gas distribution system where a gas containing ozone is distributed into the vicinity of outdoor kiwifruit vines to treat the bacterial disease Pseudomonas syringae pv actinidiae (PSA). The method and apparatus is suitable for treatment of vines growing outside The gas or air distribution system for an outdoor orchard, has ducts positioned about the outdoor plant growing environment and a fan attached to or located inside a feed duct forming part of the ducts for pumping gas into the ducts which are arranged to direct the gas-flow and to release the gas into the outdoor plant growing environment. A sensor in at least one of the ducts or in the outdoor plant growing environment means controls the gas distributed to growing plants in the outdoor plant growing environment dependent on an output of the sensor. The ducts comprise a network of interconnected pipes of flexible material arranged to direct the gas-flow with perforations for releasing the gas. The duct perforations are positioned adjacent the growing plants at ground level. The ducts are positioned over the plants.
