Kiwifruit growers say test results indicating a vine-killing disease may have been in New Zealand for several years suggest it can be managed.
MAF Biosecurity has found positive results for the bacteria PSA in pollen samples collected as far back as 2007.
Fifty-one orchards have tested positive for the disease.
Kiwifruit Growers Association president Peter Ombler says the MAF discovery could be good news for the industry because it shows vines have been living with the disease and the impact may not be as devastating as earlier feared.
However, questions remain about why some orchards are experiencing worse symptoms this year and the serious cases show an aggressive strategy is needed to stop PSA levels getting out of control, he says.
Kiwifruit marketing company Zespri says news that the disease may have been present for several years suggests the current outbreak could have been triggered by environmental conditions.
Director of corporate and grower services Carol Ward says overseas experience shows PSA can lie dormant at times.
Ms Ward says it is not yet known what has triggered the more severe symptoms in a few orchards this year, but it could be weather-related, and the industry needs to act urgently to keep bacteria at manageable levels.
Zespri says 70% of tests for PSA have been negative, but scientists expect that more infected orchards will be found.
Growers are being asked to practise good orchard hygiene and monitor for symptoms. Plants with leaf spotting can be treated with copper spray, but orchardists who find more serious symptoms must cut down vines.
