Two shrubs in Guyton St, Whanganui have the fungus disease myrtle rust

Horizons staff Craig Davey (left) and Rob Sicely discuss finding myrtle rust in shrubs in the office garden. Photo / Stuart Munro

The first plants with myrtle rust have been found in Whanganui. They are ramarama shrubs at the Horizons Regional Council office in Guyton St.

The fungus disease was discovered by the site's gardener, Chris Sills, and has progressed since it was first noticed on May 14.

Because there are no other known cases of the disease within 500m the two shrubs are to be completely removed on May 17, by Ministry for Primary Industries staff.

Myrtle rust also affects feijoa trees, and the co-owner of a semi-commercial feijoa orchard at Upokongaro was caught off-balance by the news.

"I'm gutted. I don't know what we can do. Just keep an eye on our trees, I suppose. I'm going to go out now and I'm going to check those trees," Dawn Dalziel said.

The couple haven't sprayed in the past, but she said they might have to start.

Horizons plant biosecurity officer Craig Davey is surprised myrtle rust hasn't been found here earlier. Taranaki has the largest number of infected properties in New Zealand.

The disease is in Hawera and its tiny spores are easily spread by wind. There are infected plants in Feilding and Palmerston North.

It's not surprising the first find was on ramarama (Lophomyrtus) at the Horizons office.

Staff have been on the lookout for it, and ramarama has been the New Zealand plant most likely to have it.

Pohutukawa, rata, monkey apple and bottle brush are the next most common. There have only been five feijoa plants found with the disease.

There's plenty of ramarama around and it's often used in flower arrangements.

The take-home message for gardeners is to watch out for it, so they don't spread it elsewhere. Fungicides could either arrest the disease, or prevent it spreading.

Careful disposal of infected plants will be important. Burning is not an option, as it wafts spores around.

The worst that can happen is the rust can wipe out complete species, especially if there are not enough plants to ensure some will be resistant.

A Bushy Park with no Ratanui could be the result. Conservation Department staff have collected rata seed there, so that new plants can be grown if that happens.

Myrtle rust was first discovered in Kerikeri in May last year. The disease is from Brazil, and flourishes in warm, moist conditions.

Since then it has been found at 693 New Zealand properties. Taranaki has the most, followed by Auckland and the Bay of Plenty.

It affects plants of the myrtle family, including feijoa, guava, eucalyptus and manuka.

Anyone finding it should not touch it but contact the Ministry for Primary Industries by ringing 0800 80 99 66.

After destroying 5000 plants the ministry has decided the disease is too widespread to eradicate. It must now be managed instead.