PNW Pear Rootstock Research Project

2002 – 2010 Final Summary

JUSTIFICATION and OVERVIEW:

Most pear orchards in the USA have rootstocks that induce high vegetative vigor. While many of these orchards are quite old relative to other tree fruit orchards, the well-managed pear orchard continues to produce good yields of high quality fruit.  However, many do not, often because high tree vigor brings multiple production and storage problems. These include:  increased cost related to pruning, suckering, thinning and harvest labor, difficult insect management leading to additional sprays, fruit quality problems related to low fruit calcium, alternate bearing and crop loss due to post-harvest diseases that could have been greatly reduced with ground-applied fungicides a few days prior to harvest. Efforts to treat these symptoms of excessive vigor have cost a significant percentage of pear research dollars for decades, but the problems seem to remain at consistent levels. There has recently been very little obvious economic reason to change existing pear orchard systems, or even plant significant acreages of new pears.  However, over the past two decades, it has become apparent to at least some industry leaders that pear growers may be forced to replace the current 1950’s style pear orchard with either another profitable fruit, or, if they decide to stay in pear production, to grow their next pear orchard with smaller, easier to manage trees. In order to make the switch to possible semi-intensive or intensive systems, it seems obvious that dwarfing or semi-dwarfing rootstocks will be critical to the entire process, as they were to apple producers. While there had been efforts to create or test various pear rootstocks in the Pacific Northwest for several decades, and a few rootstocks in the Old Home x Farmingdale series had gained some recognition and use, there was general dissatisfaction with the speed and direction of the pear rootstock development and evaluation effort.  It was proposed that trials be placed in environments that represented the wide variation existing in the Pacific Northwest. Therefore, pear rootstocks from various sources were tested with D’Anjou, Bartlett and Bosc in trials set up in Cashmere, Tonasket and Hood River.

EXECUTIVE SUMMARY:

Full Final Report

In both trial plantings, 2002 and 2005, Old Home x Farmingdale 87 rootstock, the semi-dwarf rootstock standard at the time the trials were initiated, proved superior to the other rootstocks tested in almost every important aspect.  Health and growth of the tree were equal or better than many of the other rootstocks.  Precocity and yields were almost always superior.  Although many experienced pear growers say it produces fruit smaller than those produced on large, seedling trees, the fruit produced on OHxF 87 rooted trees was invariably large, at times too large, and even with recent high yields of 70 – 90 bins per acre equivalence, has shown no trend toward smaller size. The precocity brought on by this root might cause oversetting of fruit in the early years of orchard establishment, leading to runting of the tree and subsequent smaller fruit size, but that scenario did not play out in the nine seasons of testing with Bartlett, Bosc and D’Anjou. This rootstock is not the equivalent of the Malling 9 in apples, it is perhaps more the equivalent of M 106; better by far than seedling or OHxF 97, but not what the industry is ultimately hoping to find.

The Pyro 2-33 and OHxF 40 vied for second place in over-all performance. The OHxF 40 probably did fairly well under the conditions of the trial (10 foot row spacing) because it is a fairly large tree, and had more bearing surface in the early years.  Yield efficiency lagged behind other rootstocks in many of the test years and sites. Pyro 2-33 trended toward being more dwarfing than OHxF 87, and in some of the trials and years, had equivalent yield efficiency. It was the superior rootstock for free standing, central leader Bartletts, as it produced a tree that bloomed sufficiently for yield, but not in excess, leading to much simpler hand thinning, and usually larger fruit.

Perhaps as important as finding the top performers of the world’s then-available rootstocks was the discovery of the limitations of those that performed poorly. Some of the rootstocks, such as the Fox 11 and 16, were neither bad nor good in any aspect we were looking for. Others, such as 708-36, BU-2 and BU-3 had serious problems with pear decline in the North Central Washington plots. However, Pyrodwarf, which was lightly tested for only several years prior to its release, and was being sold during the first few years of this trial, demonstrated some important deficiencies. While it often was one of the least precocious rootstocks in the trials, with subsequent low yields and relatively vigorous growth, the fruit size trended towards last place in the trials most seasons. In a few infrequent instances, the fruit size induced by Pyrodwarf has been competitive in a specific trial or season. Finally, under almost every Pyrodwarf-rooted pear tree in the plot are numerous, vigorous and thorny root suckers that are unpleasant to work around and would require yearly attention.

Pear growers will benefit from the discovery of a practical semi-dwarf pear rootstock much as the apple growers did when apple production switched from using seedling rootstock to using more manageable and productive semi-dwarf roots such as Malling 106, but the pear grower will not face the collar rot issues that came with M 106. Semi-dwarfing apple rootstocks were not the final horticultural answer to apple growers, as they soon turned to more dwarfing rootstocks that were available. At this time, there is no M9 equivalent in pear rootstocks, so until a better pear rootstock is developed, we will need to better identify, understand and work with the best amongst the current semi-dwarf pear rootstock choices.

Details:

In 2002, after several years of preliminary effort, a pear rootstock trial was established in four locations in the Pacific Northwest. Grower cooperators provided sites in Tonasket (Bosc) and Cashmere (D’Anjou), one trial was established on the TFRC property in the mid-Yakima Valley (Bartlett grown as for processing), and one trial was planted in Hood River at the OSU-MCREC in Hood River (D’Anjou). Seven rootstocks were included the first season, and an additional four were planted on these sites in 2005. The trees/rootstocks have been evaluated on the following:

1. Survival
2. Suckering
3. Tree size (trunk cross sectional area)
4. Yield
5. Fruit size

Virtual Tours of the Various Trial Sites: (Under Constant Construction)

• Tonasket – Bosc
• Cashmere – D’Anjou

Rootstocks included:

As this was not considered a training systems trial, there was no effort to study the scion/rootstock behavior in an intensive, on-wire, formal training system. That effort would require many more trees than are available on these specific rootstocks. The 2002 trees were planted 10 feet apart in the row and were trained in a free-standing central leader. To date, the “semi-dwarf” plot trees in this system are generally healthy, but much less vegetatively vigorous than the standards of the industry. Most of the trees appear as if they would have been quite appropriate if planted at 6 – 8 feet in row and 14 – 16 foot row spacing, with no wire support. As this was not considered a training systems trial, there was no effort to study the scion/rootstock behavior in an intensive, on-wire, formal training system. That effort would require many more trees than are available on these specific rootstocks. The 2002 trees were planted 10 feet apart in the row and were trained in a free-standing central leader to study tree growth without root competition. The “semi-dwarf” plot trees in this system are generally healthy, but are much less vegetatively vigorous than the standards of the industry.

Scaffold limbs have been spread early in the training years, and may be almost as productive as if they had been placed on wire support. In recognition of this, in the D’Anjou trial at Cashmere and the Bosc trial in Tonasket, the 2005 trees were planted at 6 foot row spacings, and were trained to wire starting in 2006 (a year too late). The 2005 D’Anjou rootstock trial in Hood River was planted at the wider spacing standard of this trial, and may serve as a contrast of rootstock behavior on intensive vs. semi-intensive systems. Pruning and training at all four trial sites has been directed or carried out by local experts, with the intention of bringing the trees into early production, while building a proper framework for the free-standing system.

Since 2002, some survival and root suckering problems have emerged, which may have eliminated some of the rootstocks prior to commercialization. Yields began in the third year, and were significant in the fourth leaf. By 2007, some of the 2002 rootstocks will probably be judged lacking in various important attributes, and the degree of evaluation reduced or dropped entirely. More firm conclusions on the two or three more promising rootstocks will require at least 2007 data, and the sixth and seventh leaf data will likely separate and solidify fruit size differences. The 2005 planted rootstocks will be producing fruit in 2007-2011. Some of these rootstocks have been trained on a 4-wire, 10 foot high trellis.

The trials have been carried through their ninth season; have now reached the years when yield and fruit quality data is most abundant, and constitute a significant investment of time, money and land by grower cooperators and researchers. 2009 fruit data indicates there are both very promising possibilities and potentially serious problems in current commercial rootstocks . If these trends continue in the older trees, the data will become crucial to nurseries and growers making informed rootstock decisions over the next decade. In the longer term, the quest for the perfect PNW pear rootstock of the future continues. Perhaps that root currently resides in the trial, but that remains to be determined. Positive results from this trial will serve to encourage both the nurseries and the growers to plant rootstocks that have the greatest potential in the intensive pear systems trials that will be planted in the near future. The perfect rootstock does not appear to be available, but we can work with the current choices until something beter comes along.

Picture:  Ninth year D’Anjou Pear with the equvalent of 73,400 lbs. of  fruit per acre. Fruit size was large, tree returned with a simiar yield in its 10th year.