Development of Organic Production Practices for Pawpaw on Selected Rootstocks

Development of Organic Production Practices for Pawpaw on Selected Rootstocks

Summary

Pawpaw is a unique native tree fruit that is resistant to many diseases and insect pests, making this crop attractive to organic farmers. However, little information concerning organic production of pawpaw is available. Pawpaw cultivars with excellent fruit quality are usually propagated commercially by grafting cultivar buds (scions) onto common seedling rootstock of diverse genetic origin. In regional variety trials, the pawpaw cultivars PA-Golden and Sunflower have produced fruit earlier than other cultivars. Rootstocks produced from open pollinated seed from these cultivars could promote early bearing of grafted scions (cultivars) and result in early fruit production for farmers. The goal of this project is to develop organic horticultural practices with selected pawpaw rootstocks in an effort to promote earlier bearing and consistent tree performance, and longer tree life for organic and limited resource farmers.

Objectives/Performance Targets

Objective 1. To determine the optimal application rate of organic nitrogen (fish emulsion) that enhances tree establishment, growth, early flowering, and fruit production in the orchard.

Objective 2. To determine if flame cultivation can be used effectively compared to glyphosate (RoundUp) application for weed control to promote pawpaw tree establishment and growth in orchards.

Objective 3. To determine if seedling rootstocks derived from two pawpaw cultivars (‘PA-Golden’ and ‘Sunflower’) will enhance tree survival, growth, flowering, fruit set, and fruit size of four pawpaw cultivars (PA-Golden, Sunflower, Shenandoah, and K8-2) compared to rootstock produced from commercially available mixed seed. Plantings for this objective will be established at six sites in three states (KY, VA and NC), including sites at Kentucky State University, University of Kentucky, and four farms. All sites will serve as demonstration orchards in the future for pawpaw production for limited resource and organic farmers.

Accomplishments/Milestones

A planting was established at KSU on April 18, 2005 to determine the optimal application rate of organic nitrogen that would enhance tree establishment, growth, early flowering, and fruit production in the orchard. Pawpaw seedlings were planted and 5 levels of organic N were applied to determine the optimal application rate. Survival of this planting was evaluated in late September, 2005. An average of 50% of this planting survived, possibly due to the small size of the trees and drought conditions. The greatest survival was in the trees treated with 4 oz and 0 oz of N, at 58% survival; with only 33% of trees treated with 2 oz of nitrogen surviving. Data will continue to be taken on this planting for the next three years. A companion planting will also be established for the nitrogen study at KSU in 2006.

A planting was established on April 19 to determine if flame cultivation can be used effectively compared to glyphosate application for weed control to promote pawpaw tree establishment and growth in orchards. One year old grafted pawpaw trees were planted and assigned weed control treatments of flame cultivation, wood chip mulching, or control. Flame cultivation fatally damaged the trees. Older (3 year old) trees were also subjected to flame cultivation and showed trunk damage, but not death, and weeds were controlled. PVC pipe will be used in an experiment to protect trees from flame damage in 2006.

In an effort to determine if seedling rootstocks derived from various pawpaw cultivars will enhance tree survival, growth, flowering, fruit set, and fruit size of four pawpaw cultivars compared to rootstock produced from commercially available mixed seed, two plantings were established in April and May, 2005. At KSU, grafted trees of two rootstocks and four different scions were planted to determine the effect of rootstock seedling source on scion growth. The planting was mulched with wood chip mulch and irrigation was installed. Mortality of this planting was evaluated in late September, 2005. An average of 35% of these trees survived. The combination with the highest survival rate was Sunflower grafted onto Sunflower seedlings, with a survival rate of 38%, while the highest mortality rate was with PA Golden grafted onto Sunflower rootstock, with a survival of 32% (68% mortality). Replacement trees are available and in 2006 we will replace dead trees in the planting. Fifty-nine trees were also planted at the University of Kentucky (UK) research farm in the SARE rootstock study. Of these, 30 trees survived; a survival rate of 50.8%. In 2006, replacement trees will be planted for those that were lost. Additionally, 750 trees for each of three rootstocks were grown in the greenhouse in 2005 and over-wintered. These trees will be budded with three cultivars and fall planted at three grower sites in the fall of 2006. All sites will serve as demonstration orchards in the future for pawpaw production for limited resource and organic farmers.

Pawpaw workshops were held on August 18 and September 15 at the KSU Research Farm in Frankfort, Kentucky. Approximately 100 people attended each event, including tobacco farmers, producers for farmer’s markets, home gardeners, university faculty and members of the press. Several growers involved with the SARE study held a roundtable discussion during the workshop. There was a Propagation Roundtable that discussed seedling and clonal propagation methods used in this SARE study, as well as a demonstration on how to bud pawpaw rootstock. Participants also tasted over 20 pawpaw fruit varieties, toured the Kentucky State University orchards and sampled pawpaw ice cream. A summary of the SARE pawpaw research efforts was also presented at the Ohio Annual Pawpaw Festival in Albany, OH on September 17-18, 2005. About 2000 people attended the festival. A web site describing the project has been constructed and can be found at: http://www.pawpaw.kysu.edu/sare.htm

Impacts and Contributions/Outcomes

Small family farmers in the southeastern United States are attempting to find alternative crops for their long-term economic viability with the end of the tobacco support system. Pawpaw has potential for farmers in the southern region of the United States as a high-value fruit crop for processing and fresh market sales. Little scientifically derived information is available concerning organic production of pawpaw. Development of organic production recommendations should assist growers in the development of pawpaw as a niche organic crop. The development of rootstocks that will lead to early fruit production of cultivars, by 3 years after planting instead of 4 to 5 years, will increase early income from new plantings and assist the development of pawpaw as a commercially viable crop. Development of organic orchard management methods will allow farmers to adopt economically viable, environmentally sound and socially responsible practices. Workshops were held to discuss organic pawpaw growing that provided farmers with the knowledge to successfully grow and market pawpaw as a new niche crop.

Collaborators: