There is an increased interest among North American consumers for locally grown foods, including organic produce and specialty, heirloom or “ethnic” vegetables. Some farmers seek to fill the demand created by these niche markets, but in some cases must compete with similar products grown elsewhere. Sweetpotato has potential for low-input or organic production to supply local markets, because of low nitrogen (N) fertilizer requirements [Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), 2010] compared with many other vegetables and because it currently has few diseases and pests in regions where sweetpotato is not widely grown. Indeed, sweetpotato is in a different plant family (Convolvulaceae) from most other crops, which may make it ideal for crop rotation in organic production systems. This may allow producers, including small-scale growers, to tap into local markets by selling sweetpotatoes in farmers’ markets or through other forms of direct marketing.
Sweetpotato is one of the most important crops worldwide (Lebot, 2009). Currently, China is the leading producer with ≈70% of the World’s annual crop of over 100 million tonnes (Food and Agriculture Organization of the United Nations, 2013). In North America, over 90% of production is concentrated in the southeastern United States (mainly North Carolina, Mississippi, and Louisiana) and in California [U.S. Department of Agriculture (USDA), 2011a]. Thus, most sweetpotatoes consumed in Canada and the northern tier of the United States are shipped long distances to reach these northern markets. Indeed, ≈70% of U.S. sweetpotato exports are destined for Canada (USDA, 2011a). Consumption of sweetpotatoes in North America has greatly increased over the past decade. In the United States, per capita consumption has increased from 4.7 lb in 2003 to 6.4 lb in 2011 (USDA, 2011b). In Canada, consumption has doubled in the past 10 years reaching 1.4 kg per person per year in 2013 (Statistics Canada, 2014). North American consumers have an increased interest in the sweetpotato in part because of its nutritional value: it is a good source of beta-carotene and dietary fiber and has a low glycemic index (Bovell-Benjamin, 2007; Lebot, 2009).
Currently, there is little sweetpotato production in areas with cool temperate climates such as Canada or the northern United States. Indeed, this crop requires a long, hot growing season to achieve maximum yields (Lebot, 2009). To compensate for the cooler, shorter growing season in Canada and the northern United States, growers may adopt some or all of the following strategies: using black plastic mulch, planting rooted cuttings, or choosing early-maturing cultivars.
In the relatively cool climates of Croatia (Novak et al., 2007) and Massachusetts (Hochmuth and Howell, 1983), the use of black plastic mulches significantly increased marketable yields of sweetpotato because of increased soil temperatures. Eguchi et al. (1994) found that yields of sweetpotato were higher at soil temperatures of 24 °C than at 20 or 22 °C. Mulches also have the added advantage of suppressing weed growth. One disadvantage is that the mulch must be removed before harvest, but this problem can be circumvented by using biodegradable mulch that will at least partially decompose before harvest.
Sweetpotato can be propagated by planting rooted cuttings or “plugs” instead of the more commonly used unrooted “slips.” Bornt (2012) in New York State and Novak et al. (2007) in Croatia found that using rooted cuttings or transplants instead of slips led to higher yields and larger storage roots. The larger initial root mass on rooted cuttings may encourage faster early growth compared with that obtained with slips (Novak et al., 2007).
Sweetpotato cultivars vary widely in terms of their yield and required length of growing season, which ranges from 3 to 6 months (Lebot, 2009; OMAFRA, 2010). ‘Beauregard’, ‘Evangeline’, ‘Georgia Jet’, ‘Ginseng Red’, and ‘O’Henry’ may be considered early maturing (90–100 d) according to the Sand Hill Preservation Center (2015). It should be noted that sweetpotato does not have a specific maturity date as the plant and its storage roots grow indeterminately as long as growing conditions are adequate (Lebot, 2009). Beauregard (Rolston et al., 1987) was the most widely grown cultivar in North America; although recently, Covington (Yencho et al., 2008) has become more popular in North Carolina. Most cultivar trials in North America have been conducted in the main sweetpotato growing areas which have long, hot growing seasons (National Sweetpotato Collaborators Group, 2012) although a few trials have been conducted in Ontario (Filotas, 2012), New Hampshire (Sideman, 2013), New York State (Bornt, 2012), and the Maritime Provinces of Canada (Zvalo et al., 2012). However, to our knowledge, there are no peer-reviewed reports of commercial cultivar trials conducted in eastern North America north of the 45th parallel. Cultivar recommendations for cool environments in North America vary. In Ontario, ‘Beauregard’ and ‘Covington’ are recommended (OMAFRA, 2010). In New Hampshire, Grube (2009) suggested ‘Beauregard’, ‘Covington’, ‘Georgia Jet’, ‘Japanese Yam’, and possibly ‘O’Henry’ and ‘Carolina Ruby’. In New York State, Bornt (2012) reported that in 2010 Georgia Jet was the most common cultivar, followed by Beauregard; but a subsequent survey in 2012 found that Beauregard and Covington had become the most common.
The goal of this project was to assess the potential yields and quality of sweetpotato grown in a cool, temperate climate, located in eastern Canada much farther north than traditional production areas, in a pesticide-free production system using black plastic mulch and rooted transplants. Although not completely organic, our test site has been certified by Local Food Plus (Land Food People Foundation, 2014) since 2011, which limits the use of certain inputs such as pesticides. We also evaluated the yields and quality of 15 sweetpotato cultivars and selected lines including common orange-fleshed types, some heirloom cultivars, and some specialty types with yellow or white flesh. Although less well known among North American consumers, yellow and white cultivars may present market opportunities (Leksrisompong et al., 2012). Finally, we wanted to observe which pests and diseases would develop in the absence of pesticides.
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