Dec 3, 2010
Rootstock availability key to pears

Recently, several new semi-dwarfing rootstocks have become available to growers in the United States, which could be used in higher-density growing systems, similar to what has been done in apples.

Traditionally, pear orchards in the United States have been low-density, with 150 trees to the acre or less. These trees are planted on seedling rootstocks, which have a low early production, low mature yields and are slow to reach any levels that will produce, Cornell University researcher Terence Robinson said.

Robinson ran a field trial in Geneva, N.Y., comparing four training systems/densities. They were: central leader at 243 trees per acre; vertical axis at 519 trees per acre; tall spindle at 908 trees per acre; and super spindle at 2,179 trees per acre.

The trials were on six dwarfing rootstocks – seedling, OHF97, OHF87, Pyrodwarf, Pyro 2-33 and Quince A – with three varieties: Bartlett, Bosc and Taylor’s Gold.

In Robinson’s experiment, tree density had a largely positive effect on yield in the third and fourth years, with Bartlett on OHF87 or Bosc on Pyrodwarf achieving 60 tons per hectare in the fourth year, he said. In contrast, the lowest-density system (central leader) had only 10 percent of the yield of the highest-density system. Robinson said there was a significant interaction of rootstock and variety, with OHF87 being the best rootstock for Bartlett and Pyrodwarf performing best with Bosc and Taylor’s Gold.

The main issue Robinson saw in the blocks was that fruit size was negatively related to planting density. The super spindle system produced significantly smaller fruit than either the vertical axis or the central leader. Part of the effect was due to greater crop loads on the super spindle system. However, when fruit size was adjusted for crop load there was still a negative effect of planting density on the fruit size of Bartlett, he said.

Robinson isn’t the only researcher looking at higher-density pears. Oregon State University (OSU) Extension faculty are growing shorter trees – 8 to 11 feet tall, compared to the usual 16-footers – that are three times closer together than in normal orchards and against wire frames.

“We built economic parameters to compete in the global economy,” said Clark Seavert, OSU Extension agricultural economist. “This is the first time in the Oregon pear industry that a project was driven by economics.”

“We are presently investigating several research lines relating to high-density pear systems,” said Todd Einhorn, an assistant professor at OSU. “None of which are at a point where we can draw conclusions.”

Seavert and Tom Auvil established a high-density, planar, trellis block of pears at an Oregon research station in 2005, Einhorn said. The system has not provided the early net returns to justify establishment costs. The majority of that planting was Anjou.

Einhorn has also considered rootstocks as a factor. They have not collected yield/cropping data on the planting because, at least for Anjou, it does not appear to be the appropriate training system. They have started to investigate some of the factors that they have identified as limiting Anjou on a horizontal wire system, he said.

According to USA Pear, a pear growers’ marketing group, the United States is the world’s third largest pear-growing nation. Most of these pears are being grown in Oregon and Washington state. However, pear growers in other countries have learned to use the same high-density systems that have worked well for apples. One of the limitations has been the availability of dwarfing rootstocks.

Regions outside of the Northwest are not known for pears. Oregon and Washington make up the largest pear-producing region, with roughly 84 percent of all fresh pears grown in the United States – and more than 94 percent of all winter pears. That area also accounts for 92 percent of America’s fresh pear exports, according to USA Pear.

What is it about the Northwest that makes it successful with pears? Can growers in other regions be as competitive with pears as they have been with apples? These are questions Robinson seeks to answer.

Derrek Sigler




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