Final report for LS14-265
Project Information
Pawpaw, a tree fruit native to the Eastern U.S., is in small-scale commercial production with its popularity on the rise. Pawpaw fruit have fresh market appeal for farmers markets and Community Supported Agriculture (CSAs), and processing appeal for frozen pulp production for sale to gourmet restaurants. Many small farmers have seedling pawpaw trees or wild trees that produce small yields and low quality fruit. New commercially available pawpaw varieties are now available and new cultivars are being developed that will increase yield, fruit quality, and consumer demand.
There are over 100 limited resource farmers in Kentucky alone who have small plantings of seedling pawpaw trees or wild trees that with grafting and top working could serve as rootstock and enable rapid production from grafts of high quality and high demand pawpaw fruit. Bark inlay is a grafting technique which allows the union of a rootstock limb or trunk (at least 1 to 2 inches in diameter) that is much larger in size than the scion piece. This technique has been used by apple producers to change the variety of an existing orchard (top working), adding a branch of an untested scion cultivar to an existing tree for observation, or repairing a tree that may have had a branch broken off by storm damage or fruit overloading. This technique has not been well developed for pawpaw and represents a method for growers to change over to higher yielding and high quality fruit cultivars.
Experiments will be conducted using established seedling trees with methods to reduce negative effects of spring heating of grafts, as well as improve timing for successful spring grafting and cultivar selection to optimize this technique for farmers. The objectives of this proposal are to: 1) develop methods to optimize bark inlay grafting success by cultivar, grafting time, and heat reduction on grafts on large pawpaw seedling rootstock trees in the field at KSU and grower locations, 2) examine scion take, flowering, and fruiting response time of varieties propagated by inlay grafting, and 3) create extension bulletins and YouTube videos concerning how to successfully graft and top work pawpaws and offer to growers; hands on grafting workshops will also be offered. Grower trials will serve as demonstrations and workshop sites in coordination with the Kentucky Nut Growers Association and the Ohio Pawpaw Growers Association. This proposal will not only increase yields but will enhance high quality marketable fruit; thereby promoting a sustainable fruit production system with low inputs for limited resource farmers.
1) Develop methods to optimize bark inlay grafting success by cultivar, grafting time, and heat reduction on grafts on large pawpaw seedling rootstock trees in the field at KSU and grower locations,
2) Examine scion take, flowering, and fruiting response time of varieties propagated by inlay grafting to select for easy to propagate varieties,
3) Create extension bulletins and YouTube videos concerning how to successfully graft and top work pawpaws and offer to growers; hands on grafting workshops and “Third Thursday” workshops.
Cooperators
Research
Three commercially available pawpaw cultivars with large, high quality fruit and high yields were selected: ‘KSU-Atwood’, ‘Sunflower’, and ‘Susquehanna’. Three trees of each cultivar were grafted on two dates, early vs. late May at the Kentucky State University H.R. Benson Research and Demonstration Farm in 2016, 2017, and 2018.
In 2016, trees grafted using the bark inlay method in early May (May 3, 2016) had a survival of 78%, compared to trees grafted in late May (May 23, 2016) with a survival rate of 67%. Scions of trees grafted in early May had grown an average of 1.2 m, while scions of trees grafted in late May grew an average of 0.83 m. Precocious flowering and fruit production 2 years after grafting was seen in trees grafted in early May. For this experiment, 57% of trees grafted in early May 2016 flowered in spring 2018, with an average of 14 flower buds per tree; 33% of trees grafted in late May 2016 flowered in spring 2018, with an average of 1 flower bud per tree. Trees grafted in early May 2016 had more vigorous scion growth and more flower buds per tree in 2018. Only trees grafted in early May produced fruit in 2018, only 2 years after grafting, producing an average of 12 fruit per tree. Grafted pawpaw trees generally flower and fruit 3-4 years after grafting, so flowering at 2 years is considered precocious.
For 2017, trees grafted using the bark inlay method in early May (May 2, 2017) had a success rate of 78%, whereas trees grafted in late May (May 26, 2017) had a success rate of 44% (with one graft not surviving the winter for a survival rate of 33%). Growth was similar between the two dates, with scions grafted in early May growing an average of 0.53 m, while scions grafted in late May grew an average of 0.57 m.
In 2018, we again saw confirmation that early May is preferable to late May for bark inlay grafting of pawpaw. Seventy-eight percent of trees grafted in early May (May 1, 2018) were successful compared to 33% of trees grafted in late May (May 31, 2018). No differences were seen among cultivars. Again, growth was similar between the two grafting dates, with scions grafted in early May growing an average of 0.35 m, while scions grafted in late May grew an average of 0.30 m. Several scions broke in a wind storm on July 20, 2018 with recorded wind gusts of over 60 mph recorded at the KSU farm, which caused the loss of several grafts, and shorter scion height than in previous years.
Due to a higher success rate, greater growth, and more precocious flowering and fruit production, early May is preferable to late May for performing bark inlay grafting of pawpaw trees. Staking the grafts securely is essential to prevent breakage from strong winds.
Education
Create extension bulletins and YouTube videos concerning how to successfully graft and top work pawpaws and offer to growers; hands on grafting workshops and “Third Thursday” workshops.
Educational & Outreach Activities
Participation Summary:
A video was recorded of the grafting process in May 2016 with Mr. Neal Peterson demonstrating the bark inlay method. The video has been posted on the KSU website and social media and has 2,005 views to date (https://vimeo.com/236955626). An instructional handout has been developed of the bark inlay grafting method and distributed at grafting workshops. This handout is in the process of being further expanded into an extension bulletin and will be completed by December 2018.
A demonstration orchard was grafted at the University of Kentucky Robinson Center for Appalachian Resource Sustainability (UK-RCARS) in Jackson, KY on May 2, 2018. The orchard consisted of sixty 3 year old seedlings and was grafted using the bark inlay method, cleft grafting, whip and tongue, or chip budding depending on the size of the rootstock. Six each of ten cultivars and advanced selections were grafted onto seedling rootstock to improve fruit production and serve as a demonstration orchard for visitors and workshop participants to see various grafting methods and orchard management techniques. 67% of the grafts were successful.
Three grafting workshops were conducted as part of this grant, reaching 92 people. The first grafting workshop was held at the Kentucky State University H.R. Benson Research and Demonstration farm on May 5, 2017. Thirty-one people attended the workshop and learned hands-on bark inlay grafting of pawpaw in the field, and chip budding and cleft grafting of potted trees. Attendees were able to graft two pawpaw trees to take home for planting. The workshop was repeated on May 4, 2018, with thirty-two people in attendance to learn hands-on bark inlay grafting, chip budding, and cleft graft using a grafting tool at the KSU farm. A third pawpaw grafting workshop was held at UK-RCARS in Jackson, KY on May 14, 2018, with 29 participants. Workshop participants at all 3 workshops received a grafting knife and tool to enable them to continue grafting at their own farm or home.
Scionwood of 16 cultivars and advanced selections was collected in March of each year for grafting demonstrations and trials and distribution to nurseries and individuals.
Data was published in the University of Kentucky Fruit and Vegetable Research report, Kentucky Nut Growers Association Newsletter, and American Society for Horticultural Science; and presented at the American Society for Horticultural Science annual meetings in 2016, 2017, and 2018 and Kentucky Academy of Science in 2018 (see citations below). Orchard tours showing the bark-inlay grafted trees were conducted at the KSU Third Thursday Thing sustainable agriculture workshops in 2016, 2017, and 2018.
Publications and Presentations:
Crabtree, S., J. Lowe, and K. Pomper. 2018. Grafting success of eleven pawpaw cultivars and advanced selections using four grafting methods. Sheri Crabtree, Jeremy Lowe, and Kirk Pomper. Kentucky Academy of Science Annual Meeting, November 2, 2018.
Behrends, M., Grafting Pawpaw (Asimina triloba). Matt Behrends,Third Thursday Thing Sustainable Agriculture Workshop, September 20, 2018.
Behrends, M., K. Pomper, J. Lowe, and S. Crabtree. 2018. Timing of grafting and grafting method of pawpaw affects success rate. American Society for Horticultural Science annual meeting, Washington, DC, July 31-August 3, 2018.
Crabtree, S.B., J.D. Lowe, K.W. Pomper, and R.N. Peterson. 2017. Timing of Bark Inlay Grafting of Pawpaw Affects Success Rate. University of Kentucky Fruit and Vegetable 2017 Annual Research Report PR-739, pp. 15-16.
Crabtree, S. 2017. Bark Inlay Grafting: A promising new technique for pawpaw propagation. The Kentucky Colonels Kernel, Kentucky Nut Grower Association Newsletter. 2-47:1, pg 3-4.
Crabtree, S., Lowe, J., K. Pomper, and R. N. Peterson. 2017. Timing of Bark Inlay Grafting of Pawpaw Affects Success Rate. American Society for Horticultural Science. https://ashs.confex.com/ashs/2017/meetingapp.cgi/Paper/26383
Crabtree, S. and R.N. Peterson. 2017. Pawpaw Grafting (video). https://vimeo.com/236955626
Crabtree, Sheri, Srijana Thapa Magar, Jeremiah Lowe, and Kirk Pomper. 2016. Jump Starting New Pawpaw Variety Production for the Industry: Developing Grafting and Top Working Approaches for Growers. American Society for Horticultural Science annual conference, Atlanta, GA, August 8-12, 2016. http://hortsci.ashspublications.org/content/suppl/2016/12/08/51.9.DC1/2016_HS_Conference_Abstr_Supplement.pdf
Learning Outcomes
Grafting knowledge and horticulture production skills with the tree fruit pawpaw.
Project Outcomes
Impacts
Many limited resource farmers in Kentucky have small plantings of seedling pawpaw trees or wild trees that with grafting and top working could serve as rootstock and enable rapid production from grafts of high quality and high demand pawpaw fruit. This project will not only increase pawpaw yields, but will enhance high quality marketable fruit from grower plantings; thereby promoting a sustainable fruit production system with low inputs for limited resource farmers.
Trees grafted using the bark inlay method in early May had a survival rate of 78% in all three years, whereas trees grafted in late May had a success rate of 67% in 2016, 44% in 2017, and 33% in 2018. Growth was similar between the two dates, with scions grafted in early May growing an average of 0.78 m, 0.53 m, and 0.35 m in 2016, 2017, and 2018 respectively in their first year, while scions grafted in late May grew an average of 0.76 m, 0.57 m, and 0.30 m respectively. Scion growth was less in 2018 than the previous two years due to strong storms breaking many scions in July. By year 2 trees grafted in early May had grown an average of 1.2 m compared to those grafted in late May growing 0.83 m. 57% of trees grafted in early May 2016 flowered in spring 2018, while 33% of trees grafted in late May 2016 flowered in 2018. 44% of trees grafted in early May 2016 produced fruit in 2018, while no trees grafted in late May 2016 fruited in 2018. There was not a significant correlation between diameter and graft take, or diameter and scion growth. Due to a higher success rate and more precocious flowering and fruit production, early May is preferable to late May for performing bark inlay grafting of pawpaw trees by Kentucky farmers. Staking the grafts securely is essential to prevent breakage from strong winds.