Cranberry is a low-growing vine, with a perennial growth habit (Eck, 1990). Native to North America, cranberry reproduces vegetatively by horizontal shoots (stolons), known in the cranberry industry as runners, or by shorter vertical shoots, known as uprights, produced from axillary buds (Roper and Vorsa, 1997). Individual uprights bear fruit in a biennial manner (Roper et al., 1993). After several years, uprights eventually bow under their own weight and function as runners (Eck, 1990).
Excessive vegetative growth in cranberry can be detrimental to yield (Davenport and Vorsa, 1999) as a result of shading or fungal disease. Shading has been shown to have a significant negative impact on cranberry fruit set (Roper et al., 1995), and flower bud formation depends on adequate light penetration (Roper et al., 1993). In addition to shading, excessive vegetative growth may increase the relative humidity under the canopy, resulting in a microenvironment conducive to fruit rot and other fungal diseases (Oudemans et al., 1998).
As with flower bud formation, fruit anthocyanin production depends on adequate light penetration (Strik and Poole, 1991; Toledo et al., 1993). The cranberry fruit must exceed a minimum anthocyanin content to be accepted for sale as processed fruit; extra compensation may be awarded to growers for fruit with high anthocyanin content. Due to the potentially detrimental effects of excessive vegetation, it is important to employ cultural practices that maintain good canopy architecture.
Sanding is a cultural practice used in the northeastern United States and Wisconsin to manage the cranberry plant canopy. Typically, this practice is performed every 2 to 5 years with a 0.5- to 2-inch layer of sand spread over an ice-covered bed during the winter (DeMoranville and Sandler, 2000). The sand is allowed to melt through the ice to ultimately settle on the cranberry vines so that runners are buried and rooting is encouraged. This stimulates the growth of new uprights that may bear fruit the following year (DeMoranville and Sandler, 2000). Previous studies of sanding have shown mixed results regarding potential effects on crop yield. Strik and Poole (1995) found that heavy sanding (2.5 cm) on two ‘Stevens’ beds in Oregon was detrimental to yield, while light sanding (1.3 cm) improved yield in the year after treatment at only one of the two sites. Davenport and Schiffhauer (2000) also showed that heavy sanding was detrimental. In Massachusetts, sanding decreased the percentage of light intercepted by uprights and runners and was associated with yield decreases (Lampinen and DeMoranville, 2003).
Pruning is another method that can be used for canopy management. Much like sanding, pruning opens the canopy and encourages new growth (Marucci, 1987), and has the potential benefit of breaking apical dominance, allowing lateral buds to grow (Roper et al., 1993). More uprights are produced that have the potential of fruiting the following year. Chambers (1918) performed pruning experiments on a heavily vined bed that had been steadily declining in production and reported a 10% decrease in yield in the initial year followed by a 45% increase in the following year. Strik and Poole (1991, 1992) also reported reduced yield from heavy pruning in the years of treatment but that light pruning yielded more fruit compared with the control in the following year.
While sanding and pruning have shown the potential to be beneficial, sanding has some shortcomings when compared with pruning. In addition to the high costs associated with the use of a limited resource, measurements of actual sand depths from three methods of sand application on 24 Massachusetts farms indicated a lack of uniform deposition (Hunsberger et al., 2006), which may diminish desired outcomes (e.g., uniform upright generation and pest management). Because pruning appears to accomplish the same horticultural goals as sanding with better uniformity and lower costs, it has been suggested as a replacement or supplement to sanding. However, these two practices have not been compared directly within the same cranberry bed. The objective of this study was to compare pruning and sanding treatments on ‘Stevens’ cranberry to determine effects on crop yield, economic returns, canopy characteristics, and fruit color.
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