Developing a System to Produce Organic Plug Transplants for Organic Strawberry Production

The USDA National Organic Standards require growers to use organically grown transplants for growing strawberries as an annual crop. However, organically grown strawberry plug transplants are not presently available in the U.S. or Canada. A study was conducted during fall 2002-03 wherein three types of plug mixes and fertilizers were evaluated for organic plug transplant production. Runner tips of ‘Camarosa’ strawberry were obtained from a nursery in North Carolina and planted in propagation trays. Our research demonstrated that good quality organic plug transplants can be produced under low-cost polyhouses by using organic plug mixes and organic fertilizers. Plants grown in a plug-mix containing ¼” pinebark and worm castings (1:1 v/v) needed to be irrigated more frequently as compared to those grown in plug mixes that contained untreated peat moss, coarse perlite, and medium vermiculite (2:1:1 v/v). Both Fertrell Super-N (4-2-4) and Fish-O-Mega (4-2-2) when used alone produced healthy transplants but caused ‘leaf burn’ when used together. Therefore, when used in combination, the concentrations of Fertrell Super-N and Fish-O-Mega may need to be reduced in order to avoid leaf burn. The cultivar used in this study (‘Camarosa’) is highly susceptible to anthracnose fruit rot disease which was a severe problem during the unusually wet and cold fall of 2002-03. Regardless of the type of plug-mix or fertilizer used, the non-marketable yields were greater than the marketable yields since many fruits that would have otherwise been marketable were rendered unfit for the market due to the severe outbreak of anthracnose fruit rot disease. Therefore, selecting cultivars that are resistant to anthracnose fruit rot will be necessary for organic strawberry cultivation in Florida. Disinfection of the runner tips prior to plug production by dipping in dilute solutions of Oxidate® or Chlorox® bleach may help reduce the incidence of this disease, and may ultimately result in improved yields.

Introduction

In the Southern region, strawberries are grown as an annual crop. Most of the production is done in Florida (6,900 acres) and North Carolina (1,800 acres), and small scale farmers in many other states grow strawberries as a cash crop for direct marketing. Even though strawberries are one of the most popular fruits in the United States, they are listed among the ten most avoidable foods due to high pesticide residues (Ames and Born, 2000). Methyl bromide, which is a class I ozone depleting substance and will be phased out by January 2005, is used as a soil-fumigant in 90% of the total strawberry acreage in Florida (ERS / USDA, 1999). Consumer awareness about the advantages of pesticide-free, organically grown produce is increasing and many consumers are willing to pay a premium price for organically grown strawberries (Pritts and Kovach, 2000). Organic strawberry production without methyl bromide can be an economically viable alternative for strawberry growers who wish to adopt an alternative method of strawberry production in the post-methyl bromide era. As a matter of fact, most organic strawberry growers use plug transplants produced in North Carolina or Nova Scotia, Canada that are not grown organically. The stock plants used in the production of these plug transplants are fumigated with methyl bromide and, the stock plants as well as the plug transplants are sprayed with synthetic pesticides. Presently, there are no wholesale transplant producers in the U.S. or Canada who can supply organically grown strawberry transplants. Organic strawberry growers have no other choice but to use conventionally grown plug transplants that have been sprayed with synthetic pesticides and derived from mother-plants that have been exposed to methyl-bromide. However, since October 2002, when the USDA National Organic Standards took effect, organic growers who grow strawberries as an annual crop are prohibited from using plugs that have been obtained from stock plants treated with prohibited materials like methyl bromide and other synthetic pesticides.

The main objective of our project was to develop a system to grow organic strawberry plug transplants that can be produced by using low-cost polyhouse structures, locally available organic plug-mixes, and organic fertilizers. Our specific objectives were:
(1) develop a system for producing organic strawberry plug transplants under two kinds of protective structures and evaluating various organic plug-mixes and fertilization programs, (2) evaluate the performance of organic plug transplants in an existing organic farm, and
(3) extend the information obtained from this study to farmers in the Southern region.