Plastic covering protects Kiwifruit from PSA

Current trials by kiwi growers in New Zealand and Italy in fighting PSA using plastic coverings have been promising. Though research is ongoing, early results have shown the plastic structures to be effective at curbing the threat of PSA to kiwi plants.

Psa is a bacterial disease that afflicts kiwifruit plants. PSA is the greatest threat to the New Zealand kiwifruit industry, according to John Holwerda, a New Zealand kiwifruit grower. "We have grafted the new Zespri variety Sun Gold and used recommended spray programmes to combat PSA, " he said. "Wind, rain and frost are the main causes of PSA spreading in our orchards and we needed to try something new," said John. The solution was a closed environment.

"PSA is a bacteria and all bacteria have tails and require moisture to be able to move on the plant surface and to enter the leaves", said Holwera. "This was the basis for the development of a plastic hoop house system to protect the vines from wind, frost and rain. Greenhouse growers throughout the world have shown that a controlled environment can go a long way toward combating bacterial disease."

The plastic roof system is that is now trialed in the kiwi orchards is up to 3 meters above the growing canopy and can be constructed over existing kiwifruit orchards. "This is basically an open plastic house and PSA may still be on the plants but deprived of wet conditions under which it thrives, it no longer decimates the protected plant", Holwerda said.

Mr Holwerda added that trials are also being conducted in Italy and experiments using Hail covers and plastic covering are being trialed. In one trial with the Zespri variety Hort 16a the plants under hail nets have had significant infection and most of the crop has been lost, however under the plastic it is expected that up to 98% of the fruit will be harvested. These results are also expected in NZ. "Although the covers are a high initial capital cost the returns, from gold kiwifruit production particularly, do justify this new technology and looks like a viable option to protect against the Kiwifruit industries greatest threat."

"It is a new technology so ongoing research will be required to help growers to understand how to grow in this new environment. Growers have started adopting covers and 30ha has been constructed this year over different varieties, altitudes and grower systems, so we should gain experience quickly", said Holwerda.