Far North avocado grower Ross Mutton is supporting industry calls for more growers to use copper spray in their orchards.

After visiting large orchards in Australia where copper applications are a key feature of fruit quality control, he's convinced the spray helps ensure avocados reach the consumer in top condition.

Mr Mutton produces about 30,000 trays of avocados annually from 16 canopy hectares of trees on 10ha he leases at Paparore, about 15km north of Kaitaia, and 9.78ha of land he owns at Houhora, about 30km further north.

Copper spraying and the removal of dead wood and plant material from around trees are essential procedures in avocado orchards.
Copper spraying and the removal of dead wood and plant material from around trees are essential procedures in avocado orchards.

He's a member of Avoco's Grower Relations Committee and was among a group of growers who travelled to Western Australia and Queensland last year to learn about methods used on three family-owned orchards, each producing more than a million trays of avocados most years.

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Most of the fruit is sold in Australia and with the families involved in marketing they understand the importance of copper spraying to prevent quality issues bouncing back from buyers to growers.

"Being at the sharp end of a call from a retailer means they'll do whatever they need to so they don't have any problems," Mr Mutton said.

"They will put their copper on, not like a lot of Kiwi growers who neglect spraying because in this country it feels like we are a long way from consumers of our exported avocados."

Copper spraying is considered the most effective way to prevent fungal rot, which starts in the orchard through infection of fruit, but usually doesn't emerge until post-harvest.

As fungal rot has been a problem over the past two seasons in New Zealand, Avoco technical manager Colin Partridge and consultant Jerome Hardy support researchers who advise it can be mitigated by growers applying copper spray and removing dead wood and plant material from around their trees.

New Zealand's wet climate and the distance of their fruit travels to market means Kiwi avocado growers must spray to preserve fruit quality. Mr Mutton said they can't afford to be complacent or avoid spraying because of the financial costs, which are around $800 a canopy hectare.

"Growers here might think their fruit won't be affected or that they're safe in the mix of a grower pool, so they don't do it," he said.

"Smaller growers in New Zealand might have a copper bill of up to $4000, but Australian growers spend a whole lot more because they are much closer to the problems when they arise.

"In reality, we have even more reasons to spray than the Australians because our fruit has further to travel, putting it at greater risk of post-harvest ripening disorders."

"Best practice" in Australia included dedicated dead wooding orchard programmes, Mr Mutton said.

Colin Partridge agreed rot control was an integrated process and orchard sanitation was very important.

"We advise growers to get rid of dead wood and mummified fruit through mulching and pruning to let light in," he said. "This, together with wind protection, trying to increase fruit calcium levels and soft fruit handling are collectively as important as copper sprays".

Avoco is New Zealand's largest avocado export supply group, with support from more than 800 growers. It is expected to export about 1.3 million trays of avocados this season.¦