When planted in the tall spindle system, high density in itself reduced tree size, and the quince rootstock at right kept trees quite small.
The market for pears in the eastern United States is good, and Terence Robinson, Cornell University’s leader in the design and management of fruit orchards, thinks eastern growers should more aggressively go for a bigger chunk of it.
While growers protest that pear production is fraught with many problems, Robinson led members of the International Fruit Tree Association up and down the alleys of pear orchards at the New York State Agricultural Experiment Station to show what can be done.
While he agrees pear growers don’t have the many rootstock choices that are available in apples, he has grown pears at very high planting densities on Old Home x Farmingdale 97 and 87, and on Quince A, Pyro 233, and Pyrodwarf.
The secret, he said, is to use the same renewal pruning methods as on apples grown on the tall spindle system, systematically taking out some large branches every year to keep the trees in their space. Pruning need not start as early as on apples, he said, but in early years, branches should be bent down below horizontal to encourage earlier bearing.
Tree height is kept down to about 11 feet, about the same as the alley width, by cutting back the leader.
While fireblight is a great concern in the humid conditions of eastern orchards, Robinson believes the disease can be managed with antibiotic sprays and by aggressively pruning out strikes. For growers entering the pear business or replanting, there are several new Bartlettlike pear cultivars that are fireblight resistant or even immune. These varieties come from the USDA breeding program at Kearneysville, West Virginia, and the Canadian breeding program at Vineland, Ontario.
“Pear orchards in the U.S. are usually low-density orchards of 150 to 250 trees per acre on seedling rootstocks, which have low early production and low mature yields,” he said. New semidwarfing rootstocks now available can be used so that high-density pear orchards can be managed like high-density apple orchards.
The trials at Geneva compared four training systems, three varieties, and six rootstocks. Here are some results:
Tree density had a large positive effect on yields in the third through eighth years. Bartlett on OHxF.87 and Bosc on Pyrodwarf were the best matches and reached yields of 1,000 bushels per acre in the fourth year. The low-density, central leader system on seedling rootstock, with 242 trees per acre, had only 10 percent of that yield.
The smallest trees were on quince rootstock, but many varieties have compatibility problems with quince. In Europe, growers solve the incompatibility problem by using compatible interstems such as Hardy or Old Home when they use quince rootstocks in super-high–density orchards, Robinson said. He has not tested that system because quince rootstocks are less winter hardy than pear rootstocks and present a risk when planted in New York State.
Despite the lack of a fully dwarfing pear rootstock, increasing tree density with semidwarfing rootstocks reduced tree size. For each of the six rootstocks tested, trees at the highest density were 55 percent the size they were in the lowest density, central leader system, Robinson said. Trees in the test orchard were planted either on a vertical axis system at 518 trees per acre, tall spindle at 908 trees per acre, or super spindle at 2,178 trees per acre.
Fruit size was smaller in high-density super spindle plantings, a negative factor. Fruit was larger on the low-density central leader and the medium-density vertical axis trees.
With Bartlett, Quince A produced the largest fruit size, and Pyrodwarf and seedling trees had smaller fruit. OHxF.97, OHxF.87, and Pyro 233 had intermediate fruit size. But with Bosc and Taylor’s Gold, there was no significant difference in fruit size among the rootstocks.
“The results of this study show that there is great potential to improve the early yield and profitability of pears with increased tree planting density and new rootstocks,” Robinson said.
The extremely high tree densities of the super spindle system produced the best yields, but tree cost may make it less profitable than the moderate density of the tall spindle system, he said.