Cranberry (Vaccinium macrocarpon Ait.) is a long-lived woody perennial with slender trailing stems that grows in acidic sandy soils. Cranberries in the United States are produced primarily in Massachusetts, Wisconsin, New Jersey, Washington, and Oregon and are important agricultural commodities for these states. Competition for resources between cranberry plants and weeds can depress cranberry yields, resulting in large annual crop losses (Patten and Wang, 1994; Swanton et al., 1993). Current weed management strategies may include cultural controls such as flooding and sanding of beds, mechanical controls such as hand weeding, and chemical controls with pre- and postemergence herbicides (Sandler, 2011b).
Interest in reducing chemical inputs into cranberry systems has provided the motivation to evaluate methods such as FC as potential nonchemical options for weed control. Flame cultivation exposes plants to brief periods of high temperature causing the water in the plant tissue to expand rapidly, rupturing plant cells. Heat is thought to disrupt and destroy cellular membranes and lead to necrosis (Daniell et al., 1969; Ellwanger et al., 1973). Many different methods of FC are available ranging from open flames to IR (radiant heat), hot foam, and boiling water. Various FC methods have been used successfully in annual crops such as carrot, corn, onion, and potato as both a pre-emergence and postemergence weed control (Diver, 2002), but little work has been done on the use of FC in cranberry.
For decades, prescribed burning has been used in perennial woody lowbush blueberry (Vaccinium myrtilloides and V. angustifolium) cultivation as a method of pruning to increase yield and aid in the control of weeds, pests, and pathogens (Eck and Childers, 1966). Historically, low-intensity burns were sometimes used on dormant cranberry vines as a way to remove old growth and stimulate new growth (Darrow et al., 1924). Although modern-day practices such as mowing have replaced this method, cranberry plants may be able to tolerate localized heat treatments primarily intended to control weeds.
Cranberry plants in a farm situation form a continuous mat of vegetation and thus present a logistical challenge for FC because weeds grow within the cranberry canopy structure. Although cranberry plants are not the target during FC treatments, treating weeds with FC may cause localized damage to cranberry plants immediately surrounding the weeds. Flame cultivation would ideally be used as a spot treatment for weeds growing in the cranberry canopy as well as on larger non-production areas where cranberry vines are not as abundant such as bed edges, ditches, and dikes.
The effect of FC on cranberry plants is not known and is an important determinant for developing recommendations for the use of FC on cranberry farms. A greenhouse study was conducted to measure cranberry response to FC in the absence of the naturally occurring variations found on cranberry farms. This study was performed in conjunction with a series of experiments testing three types of handheld propane torches (one open flame and two styles of IR) and varying exposure times on several species of perennial weeds (Ghantous et al., 2011, 2012). We hypothesized that 1) FC will cause damage to cranberry plants and that damage will increase with increasing exposure duration and vary by flame cultivator tool used; 2) cranberry plants will recover from FC treatment effect and recovery will vary with exposure duration and flame cultivator tool used; and 3) that there would be no difference in varietal response.
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