Kerikeri growers fight devastating feijoa disease

Peter Jack among the tamarillo trees he has planted to replace pulled-up feijoas. This part of the orchard used to have 80 feijoa trees producing 5 tonnes of fruit a year. Photo / Peter de Graaf

Kerikeri grower Peter Jack will be watching closely for little black and purple spots on his feijoas this summer.

The spots are signs of the devastating anthracnose fungus that has been plaguing commercial feijoa growers in the Kerikeri area.

"People think of feijoas as one of the easiest trees to grow but not now,'' Jack says.

Jack, who has been trying to manage the disease in his orchard, says his remaining trees all look wonderful at the moment and are just finishing flowering.

"Last year we started seeing signs of the disease in early January, with little purple and black spots appearing on the new fruit.''

He has removed all obviously diseased trees and replaced them with tamarillo trees. He has favoured keeping older varieties of feijoas as he believes these may be more resistant.

Jack has also been experimenting with injections of Trichoderma, which is a biocontrol agent for plant disease management.

He believes high humidity is a factor and he is hoping for a dry season to see if that makes a difference.

"As growers, we used to look forward to rain for our crops. Now we don't want rain."

Jack says anthracnose is known to affect many types of fruit but usually after harvest. The strain that is affecting the Kerikeri orchards is particularly aggressive and devastating because it affects the fruit so early before it can fully develop. It has also been observed to cause branches to die back on some trees.

He believes some growers in the area have given up and pulled out all of their trees.

Plant and Food scientists are conducting research into the aggressive anthracnose disease, with funding from the Sustainable Farming Fund.

The research, which is being led by Dr Pia Rheinlander who is New Zealand's leading expert in the disease, aims to deliver an all-round protective programme.

Potential measures include identifying cultivars with tolerance to the disease, developing a protective fungicide spray programme and developing best orchard management practices to reduce infection spread.

Peter Jack, of Kapiro, north of Kerikeri, among some of his 8 to 9-year-old self-cultivated feijoa trees. The variety on the left is Triumph, on the right Landing Rd. Photo / Peter de Graaf

Research started this year and is in collaboration with the New Zealand Feijoa Growers Association.

Dr Rheinlander says the research started in April, which was three months earlier than initially approved as researchers didn't want to miss the season.

She says initial research has targeted disease susceptibility among eight cultivars donated by growers.

"There are about 30 varieties in New Zealand but it is not possible to test all of them,'' she says.

Dr Rheinlander says initial results are showing that some varieties are less susceptible so "there absolutely is hope" for growers.

Results have to be repeated before they can be announced.

Fungicide spray combinations are also being tested at one orchard in Kerikeri.

"We've started small and over the next few years the spray testing will be extended to more orchards.''

She is hoping for some good results but researchers have already established that this is a difficult species to deal with.

She says good husbandry is vital to contain the disease, and regulations have already been put in place at her recommendations.

"The disease is spread when spores which are on the fruit are hit with rain and splashed to the next fruit so quickly removing infected material is important.

"Commercial growers need to wash and disinfect their clothes and not share plant material with other orchards.''

Humidity is a factor so canopies should be correctly pruned to promote air movement.

"This particular species of fungi has tropical origins so it likes warm and wet conditions.''

Dr Rheinlander says the disease has not yet been recorded in private backyard trees and can be difficult to distinguish from guava moth damage.

"Home owners can spray with copper but only if there is a problem.''

Association president Roger Matthews, who has a feijoa orchard in the Waikato, says the industry is struggling with the dual challenges of guava moth and anthracnose and some growers are exiting the industry.

He says the association currently has about 200 members although there are possibly another 100 commercial growers who are not members.

Currently feijoa crops are mostly sold to local markets but growers are hoping to be able to export in future.