While kiwifruit vine disease Psa shows some resistance to antibiotics, New Zealand researchers have made a breakthrough in biological controls.

As part of the Next-Generation Biopesticides program, Plant & Food Research (P&F) scientists have developed natural agents that can combat Psa from above and below ground, with field trials now underway.

With support from marketer Zespri and Kiwifruit Vine Health (KVH), P&F scientists Dr. Philip Elmer and Dr. Stephen Hoyte have identified two biological control agents (BCAs) that can significantly reduce Psa symptoms in kiwifruit vines.

"Over the last 12 months, we have identified two new foliar-applied biological control agents that protect potted kiwifruit plants against Psa in glasshouses and outdoor experiments, and in small plot field experiments," Elmer said in a release.

P&F said BCAs were a necessity for organic kiwifruit growers who wanted non-chemical control options, and also offered alternatives for managing plant pathogens that were resistant or tolerant to chemical pesticides.

The two scientists are working with AgResearch fermentation expert David Wright to find the best and most cost-effective ways of producing these BCAs, so these methods can be used for commercial production.

In the release, P&F said formulating BCAs for ease of use was challenging, but Elmer and Hoyte have developed breakthrough technology to produce a BCA that quickly dissolves in water and has a long shelf life as well as stability.

Lincoln University scientists Dr. Robert Hill and Dr. Christine Stark, and the team at the Bio-Protection Research Centre, are also using the root-dwelling beneficial fungus Trichoderma to help in the fight against Psa.

"These fungi confer to the plants a number of real benefits," Hill said.

"One is that they prime plant defence systems, so they can defend themselves better against pathogens. But they also enhance the plant’s general health and vigour."

The Crown entity said results had been promising, and the research team had isolated several strains of Trichoderma that reduced symptoms of Psa disease and improved longevity of young kiwifruit seedlings. These strains are currently being tested for efficacy against Psa in potted plant trials, alone and in combination with other BCAs.

Using Trichoderma isolates from healthy plants, the team has developed the biological control product 'TriMix-1', which is being produced at Lincoln University. The product is currently being trialed on 2,000 hectares of kiwifruit orchards in the North Island. Further mixes are currently in the testing pipeline.

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