Newspaper Article – Shorter, squatter trees near reality

Shorter, squatter trees near reality

By Geoff Mercer
Staff reporter, Hastings

Shorter, squatter apple trees planted close together to cut costs are approaching reality.

Experimental and commercial plantings of trees with a section of dwarfing rootstock grafted into the stem to reduce overall size have been made over the past three years.

The interstem section governs how large the tree will grow. The longer the interstem graft, the greater the governing effect on the tree’s size.

About six Hawke’s Bay orchards have planted trees with dwarfing rootstock grafted into them in parallel with trials conducted by HortResearch.

A Clive nursery reports increasing interest in the novel, for New Zealand anyway, approach to growing trees about three quarters the size of most in orchards now.

HortResearch scientist Dr Stuart Tustin said many growers wanted to take advantage of dwarfing rootstocks to grow smaller trees to reduce costs. They were also easier to manage.

However, no dwarfing root-stocks resistant to the pest woolly apple aphid were commercially available. To get around this, a section of Malling 9 (M9) dwarfing rootstock was grafted between a rootstock resistant to the aphid, commonly Malling Merton 106 (MM106) and budwood from the desired fruiting variety, he said.

People would notice the dwarfed trees were shorter than usual. They should grow about 3.5 metres high compared with the five-metre trees common today.

Dr Tustin said the ideal solution was to develop dwarfing root-stocks with resistance to woolly apple aphid, but achieving that was 10 years away.

It was important to grow trees on rootstocks resistant to woolly apple aphid otherwise underground reservoirs of the aphid could establish and repeatedly reinfect trees.

“Interstem grafting is a compromise until we get dwarfing stock resistant to woolly apple aphid.” About six Hawke’s Bay growers had already planted trees incorporating the dwarfing interstem, he said.

Hastings orchardist Martin Pike has two-year old trees incorporating M9 interstems growing on a Pakowhai Rd block, with Royal Gala budwood grafted above.

He said he expected slightly less vigour from the trees, more even, large-sized fruit and an eight-day earlier picking schedule.

His row spacing was 4.5 metres, with 2.5 metres between each tree. Branches grew at wider crotch angles and the tree would tend to be “squatter-coned”, he said.

“I’m aiming for an ultimate tree size of three-quarters of a Gala on MM106.”

He said there might be a risk the interstem degraded storage qualities, but Golden Delicious grown on M9 in the past had not shown any detrimental effects.

Top Trees Nursery partner Tim Barker said the nursery produced a small number of young trees with the M9 interstem last year and they had been “snapped up” by orchardists.

“It’s looking good, so we’ve increased our volume this year,” he said.

Photo caption – Dr Stuart Tustin