The modern orchard continues to elude Pacific Northwest pear growers, who lack the dwarfing, precocious rootstocks immune to sudden temperature dips and necessary for a two-dimensional canopy.
However, researchers are continuing their quest to identify rootstocks amenable to the region, narrowing the search to about 10 planted in new test blocks, and to prepare growers for a future that includes a fruiting wall for pears.
“In the long term, when more rootstocks will be available, we can have a different kind of orchard — a bit more modern, pears on trellis, like 2-D canopy, what you call a fruiting wall. But until we have this option, we need to prepare for managing a system like this,” said Stefano Musacchi, Washington State University endowed chair in tree fruit physiology and management.
“One of the major issues that a grower faces here is that when they plant the tree, they have to wait five to six years before they see a first crop,” he said. “What I want is to try to shorten this.”
Musacchi has been researching different pear systems for years, focusing on two and three leaders. “Because when I get to five, six, seven, I am a little bit concerned,” he said. “You have to know how much you have to bend without jeopardizing the growth of the vertical leader.”
For his vision, Musacchi said he must start with a good tree from the nursery, with a lot of feathers and cut back once planted. “With this system, with the bi-ax or single ax that you have pruned, you can build up the canopy very quickly,” he said.
Musacchi recommends a bi-ax when a grower wants to reduce vigor, but in poor, sandy soil where the tree doesn’t grow very well, a single ax is best.
“Following this general idea, when you are introducing a new variety, you don’t want to grow the new variety in an old-style tree,” he said. “You want something modern that can be mechanized, for harvest especially. Because honestly, the pear industry has to go in the same direction as the apple industry.”
That, of course, requires dwarfing rootstocks — something researchers have been working toward for years.
Rooting out rootstocks
Leading the effort to identify dwarfing rootstocks suitable to the Pacific Northwest is Todd Einhorn, formerly with Oregon State University and now associate professor at Michigan State University’s Horticulture Department.
Einhorn has focused his research over the years on quince rootstocks, which are commonly used for pears in Europe, and Amelanchier clones. The latter have shown promise for dwarfing qualities, production of large fruit and cold-hardiness, and new trials launched in 2016 and 2017 will evaluate interstems, but Einhorn doesn’t expect results for several years.
For quince, a selection of 22 accessions has been narrowed over several years of study to about 10 accessions planted late last spring — and essentially restarted this year to gain some uniformity among the trees — to further evaluate for dwarfing and cold-hardiness.
“Quince has a lot of potential issues with pear, but because hardiness was the most limiting factor, that’s what we decided to screen on. Once we found the hardiness levels we were screening for, we did additional work to look at potential to fight blight, then propagation studies, then compatibility work with bud grafts, and this is where we are,” Einhorn said. “Now we just have to look to the field performance and evaluate for production, dwarfing, all those things.”
Some basic questions need to be answered about these accessions to determine their suitability, he said, including: Do they collapse in one year? Do they have iron chlorosis on the root? Will they flower?
None of these accessions are rootstocks or have been used as rootstocks; for this trial, they’ve been both budded directly to d’Anjou and Bartlett and grafted to Comice as an interstem in two locations in Washington and Oregon. “There could be better interstems, but Comice I think will be OK in an effort to determine whether a direct graft looks to have issues with compatibility or whether an interstem is the way to go.”
The Parkdale, Oregon, site offers the potential for cold winter stress and a higher elevation and shorter growing season. The region doesn’t typically experience extreme cold temperatures, but rather, sharp, sudden freeze events. The soils are a bit heavier than the Washington site north of Wenatchee, so there’s more organic matter and a little more humidity and moisture.
“It will be good to evaluate the vigor in the two conditions,” Einhorn said.
The system is simple at both locations: 3 foot-by-12 foot spacing, which is high density for pears, on central leader, spindle-style trees. The goal is to see what kind of vigor control can be achieved on a central leader before researchers implement any additional horticultural techniques to control vigor, he said.
They’ve already seen some flowers on the trees this spring, so there’s little doubt the trees will be precocious, he said. Next year, they will begin quantifying flowering but knock the blooms off in order to continue to develop the canopy, with a goal of branching and filling out the canopy wire by next year.
Overall, Einhorn said he would be delighted if one of these accessions looks promising with respect to performance. “This project really is in the infancy. This is a fairly robust look, an attempt to find something promising that we can dive into a bit more. We know they are hardy, we know a little bit about fire blight susceptibility, and we have a general feeling about grafting ability,” he said. “But we have a lot to learn. In terms of producing pears in a modern, high-density, controlled system — this is what we need to figure out.” •
—by Shannon Dininny