Development of a Locally-Adapted Apple Rootstock for the Maritime Northwest

To evaluate the grafting compatibility of Malus fusca rootstocks with the domestic apple (Malus pumila) we are conducting replicated grafting trials of 40 to 46 apple varieties (with 10 replicates of each variety). Those varieties include high demand cider apples provided by the Washington State University Northwest Research and Extension Center in Mount Vernon, Washington: Amere de Berthcourt, Blanc Mollet, De Bouteville, Brown Snout, Brown Thorn, Bulmer’s Norman, Cimetiere, Court Pendu Rose, Dabinett, Domaines, Frequin Rouge, Jouveaux, Medaille D’Or, Mettais, Michelin, Muscadet de Dieppe, Muscat de Bernay, Peau de Vache, Reine des Pommes, Vilberie, and Zabergau Reinette.

Additionally, as of the January 2018 reporting we are expecting a second batch of scion varieties from Dr. Thomas Chao, at the USDA's Apple Genetic Resources Collection at Cornell University, consisting of: Sangre de Toro, Raxao, Blanquina, Teorica, Xuanina, Vedialona, Coloradona, Solarina, De la Riega, Collaos, Perico, Maria Elena, Reineta do Caravia, Repinaldo do Liebana, Pepa, Peil de Sapa, Bedan des Parts, Manchurian, Wickson, Binet Rouge, Calville Blanc, Nehou, Dolgo, Kerry Pippin, and Irish Peach.

Note that in the original proposal we had targeted only 40 varieties for grafting trails, but we have sought out six additional varieties as a back-up against grafting errors to ensure that we still meet the original project target. Additionally, we had originally planned on only 400 total grafts, but the rootstock nursery offered us a significant price break for 500 rootstocks (actually making that amount less expensive than 400) so we ordered 500 rootstocks which again will help mitigate any grafting errors and ensure that we meet the original project targets.

The Malus fusca rootstocks consist of seed-grown plants produced by a local native plant container nursery. They are 3-year transplants, having previously been harvested as bare root plants in 2016, and replanted in the field during 2017, before being re-dug in the fall. The result of this transplanting is larger caliper plants with well-developed root systems and an overall height of 18 to 36 inches. While the scion wood is being harvested and moved into cold storage at the time of the January 2018 reporting, the rootstocks are not scheduled for delivery from the nursery until March 2018. We will be contacting the nursery in an attempt to negotiate earlier delivery so that winter grafting can commence as soon as possible. Because of our region’s temperate winter climate planting can begin in mid to late winter.

Additional planting materials have been ordered and are anticipated for delivery in late January or early February 2018.

Once grafted and field planted, we will conduct monthly evaluations of grafting success over the livespan of this project, noting percent grafting success by variety to document the tolerance of various apple varieties to Malus fusca as a rootstock. Note that we have deliberately focused this project on antique and heirloom apple varieties (including heirloom cider varieties) since these offer a clear niche market opportunity for small-, midsized-, and new apple producers. Given the large-scale of establish commercial apple production, it seemed unlikely that popular dessert apple varieties such as Honeycrisp could offer an economical business opportunity for new apple producers on a new, still largely untested rootstock that is not yet widely available from commercial rootstock producers.

Our planned layout for test orchard consists of 50-foot long rows of trees, with 4-foot spacing between them and 12-foot wide alleys. We settled upon this layout after consulting with several sources, including Washington State University’s cider apple production specialists. If the majority of the grafts survive, this layout would be compatible with a hedge-style of production in which the trees are sheared with a sicklebar or hedge clipper in the spring to both maintain row configuration and to thin the apple crop. Additionally, this orchard style anticipates advancements in mechanical harvesting technology including trunk shaking and ground harvesting methods which may become more commonplace in the future.

As of December 2017, most of the new orchard block preparation has been conducted, including site clearing with a brush hog, removal of several dead trees, and clearing of the field road to the research site.

January 2019 Update: As 2018 commenced, we began a project year of big challenges, some interesting initial findings, and new questions.

Among the first unanticipated challenges we faced with was simply the toughness of Malus fusca wood. While the wood (and scions) of domestic apple varieties are soft and cut easily with a grafting knife, M. fusca is incredibly hard and challenging to cut, especially those rootstocks of thicker caliper. Grafting required constant knife sharpening, a lot of pressure, and dozens more hours than we had originally budgeted for the task. While most scion cuts could be performed in a few seconds, the rootstock cutting was a persistent bottleneck. We ended up with a number of injuries from rootstock cuts, but more critically, we had to divert a significant amount of time away from regular farm work to complete the grafting.

The second unexpected challenge was an extreme abundance and extreme shortage of water. In the first case, we faced a difficult surprise in the spring prior to planting when a neighbor’s water line burst and flooded our orchard area, making it impossible to get into the field. While we waited for conditions to dry out, the newly grafted trees remained heeled-in to a nursery bed. As conditions warmed, the trees began to leaf out, before we could transplant them. When we were able to get into our field, the weather turned unseasonably hot and the trees exhibited clear signs of heat-related transplant shock (wilting). Unfortunately, despite the early season excess of water, the summer remained warmer than average (up to 10 degrees warmer than average for extended periods) and significantly drier than normal. For context, our farm normally averages 22 inches of rain per year (we are located in a mountain rain shadow). During 2018, by our measure, the farm received less than 20 inches of rain.  

To help mitigate transplant shock and drought stress, we spent many unexpected durations of time focused on maintaining irrigation water on the trees, even as other farm work went unfinished. Disappointingly we occasionally would water the new orchard block for hours, only to dig down into the soil and still find parched dry conditions just an inch below the surface. As the summer continued, we completely wore down several plow blades on the farm in unusually dry soil, and thirsty rabbits repeatedly chewed through the irrigation lines in search of water.

Because of the dry conditions, we think that heat and water stress certainly had an impact on tree survival. Yet, overall, we are grateful that despite the many hours of unplanned work, the extra watering certainly kept many trees alive. We are hoping that future seasons will see a return to more typical precipitation.

In grafting the trees, we used standard whip/tongue graft unions, wrapped tightly in Parafilm, and held tightly with rubber bands. The tips of the scions were coated in wax to reduce desiccation. Of the scions, we were typically able to cut them down into 4 to 5 sections for grafting onto rootstocks. Because we had 2 to 3 scions for most varieties, we were able to graft 8 to 15 trees for most varieties. One observation about many of the European varieties we used (especially many French cider varieties) is that they tend to have more “blind wood” than some common dessert apple varieties. By this we mean that the spacing between buds tends to be a bit longer, allowing for fewer graft sections to be cut from a single length of scion. In general, we tried to maintain 2 to 4 buds on each scion section we grafted onto a rootstock.

In planting the trees, we supported each transplant with a 48-inch bamboo stake, and protected them with Blue-X brand tree guards consisting of a firm translucent blue plastic film that is rolled into a tube and secured with an outer plastic bag sleeve. While the cost of tree guards was reasonable (allowing them to be deployed on a large scale), the plastic does tear and photodegrade slightly faster than advertised. Because we are adjacent to expansive natural areas and the ocean, we are vigilant about the fate of plastic used on our farm. It has been a minor annoyance to find bits of broken tree guard and to have to constantly pick up and dispose of small shards.

More disappointing however, the tree guards are bird killers. On multiple instances, when removing the guards to inspect trees (which are still small enough to be completely below the top of the tree guards), we have found dead grassland songbirds which, having perched on the bamboo stakes, appear to fall into the tubes where they are unable to spread their wings and fly out. This is unacceptable to us, and we will be working on some kind of barrier for the tops of the tubes to prevent any further bird casualties before the 2019 nesting season commences. We are certain that other growers must face the same dilemma with these kinds of plastic tree guards and are disappointed that manufacturers have not engineered a solution to this problem.

It is worth noting that despite the drawbacks of plastic tree guards, they have been enormously valuable in protecting the transplants from rodents. In a few cases where wind blew some of the tree guards off, the transplants were immediately gnawed on by meadow voles and rabbits (even when the tree guard was only off for a mere day or two). This damage occurs even with very robust raptor and coyote populations on the farm. In the future, we plan on alley cropping between the orchard rows, which may change the rodent pressure for better or worse. In any case, at least on wild crabapples, rodent pressure seems to dissipate as the trees mature in size and develop thicker trunks and basal bark. In observing mature crabapples on the farm there does not appear to be any rodent damage to the trunks which will allow us to dispense with plastic tree guards. That said, if cost and labor were more competitive, we would rather be using metal hardware cloth tree guards than the plastic ones currently in use.

UPDATE – JANUARY 2020

During our 2019 season we had several significant developments in our project materials and methods:

First, we experimented with a variety of methods to improve tree guard performance, particularly to prevent songbirds from becoming trapped and dying inside the tubes. These efforts included experimenting with screened tops (which were hard to secure, with growing trees pushing them off), as well as zip-ties to partially close off the top (which turned out to be time consuming and expensive). Ultimately, we found an elegant solution in simply adding a second bamboo stake, opposite the first one, to hold up the tree guard. This solution turned out to be simple, cheap, quick to install, and a big improvement. With only one stake holding up the tree guard, the wind tended to occasionally blow them off. Two stakes prevent this, and the two stakes (positioned about 4 inches apart) are too close together for birds flapping birds to land between them, which keeps them from landing on the top rim of the guard tubes.

Second, with an eye toward continuing this project and incorporating the lessons-learned, we planted additional un-grafted rootstocks into the orchard that we will graft in future years, comparing the performance of bench grafted trees with field-grafted ones. A new working hypothesis resulting from this initial project is that as wetland-adapted plants, Malus fusca does not tolerated any significant root drying, such as occurs with normal bench grafting.

Third, we added one additional scion variety to the grafting trials in 2019, consisting of Ashmead’s kernel. In the case of grafting this variety, we tried to maintain the rootstocks in buckets of water as much as possible until they were transplanted into the field.