Wet weather in Bay of Plenty earlier this month has caused the PSA vine disease to spread more rapidly, especially across gold kiwifruit orchards.
Kiwifruit Vine Health says unseasonable rainfall introduced Psa to several gold orchards which would have otherwise produced a crop this season.
A total of 950 orchards are now Psa-positive, three-quarters of in the Te Puke area - a hot spot for the disease.
General manager John Burke says the agency will have a more complete picture of the effect of the recent rain when it has finished a regional update of all the country's kiwifruit growing regions.
He says estimates for the 2012 crop are expected in February, but at this stage it appears the gold kiwifruit harvest could be down by about 50% or 15 million trays.