Myrtle rust has been found at a nursery in Te Kuiti, King Country and three more properties in Taranaki have also tested positive, the Ministry for Primary Industries (MPI) says.
The disease at the Te Kuiti nursery was detected after MPI traced the sale of plants from another infected nursery.
Restrictions around the Te Kuiti nursery were in place and the property would be treated with fungicide
The new find, along with a further three properties in Taranaki, brought the total number of confirmed infected properties to 16 nationally.
The majority of properties were in Taranaki, with two confirmed in Northland as well as the one in King Country.
The disease-causing fungus has been found at a mix of properties, including nurseries, plant retailers and distributors, and orchard and private gardens.
MPI said it had received "unprecedented support" from members of the public, with some 420 reports of suspected symptoms to its 0800 number.
Of those reports, a small percentage required sampling and testing.
The disease has the potential to devastate native trees such as pōhutukawa and rātā, and fruit such as feijoa.