Evaluation of corn gluten meal for preemergence weed management in cranberry

Corn gluten meal (CGM) is a natural product that is typically used as a fertilizer (8-0-0), but also has reported herbicidal activity against germinating seeds. Its use as a method of preemergence weed control on cranberry farms was evaluated. The use of CGM in cranberry is a novel approach, therefore a greenhouse study was conducted to evaluate any potential phytotoxicity or harmful effects of CGM on cranberry plants prior to the establishment of a field study. With assistance from the grower, the field study was established at two sites on a recently planted organic cranberry farm in southeastern Massachusetts to evaluate if CGM suppressed new weeds. The results of this study showed that CGM was not an effective weed control on new cranberry beds, and that the addition of CGM actually led to an increase in weed biomass. Four months after the initiation on the experiment, untreated plots had an average weed biomass of 19.1 g/m², while plots which received CGM treatments averaged 109.4 g/m² (a range of 67.1 – 156.2 based on treatment). However, cranberry plants that received CGM showed a significant increase in growth, presumably from the additional nitrogen. Untreated plots had an average cranberry biomass of 3.4 g/ft², while plots which received CGM treatments averaged 7.3 g/ft² (range of 6.7 to 9.2 based on treatment). Providing adequate nutrition to organic cranberry beds is a challenge, and CGM may offer organic growers a good fertilizer option, especially when establishing new vines.

Introduction:

There is a small but interested group of growers who want to produce organic cranberries in the Northeast. Cranberry growers cite weeds as serious pests that cause yield loss in commercial cranberry production (Pest Management Strategic Plan 2001; Sandler 2010), and lack of weed control has been cited as a primary obstacle to organic production. Organic cranberry production is not a common practice in the Northeast region, and research on pest management options for organic cranberry production is lacking. Organic growers are often operating on trial-and-error, rather than scientifically based practices. Information that drives and supports recommendations for organic management is also lacking. We recognize that there are gaps in our knowledge on organic management that, when filled, would increase the sustainability of cranberry farming. As a step towards closing this gap, we evaluated if corn gluten meal (CGM), a natural product approved for use in organic farming (OMRI 2012), could be an adequate method of preemergence weed control in new bogs.

Cranberry is a long-lived woody perennial, and in well-established production areas there is little open ground; most of the problematic weeds are perennial plants as well. Because CGM works against germinating weed seeds, it would provide little control in established beds. However, newly planted bogs have a lot of open space that can be colonized by weeds germinating from seeds that have been introduced to the agroecosystem by wind, water, or sand sources. Weed control is particularly critical for new plantings (DeMoranville et al. 2001). If weeds are not controlled in this initial stage, they retard or prevent cranberry vines from becoming established (Sandler 2004), which can negatively impact fruit production. Cranberry growers have expressed dissatisfaction with some weed control options and are willing to adopt new non-chemical methods if they are shown to be effective (Ghantous and Sandler 2010).  

While conventional cranberry growers use herbicides on new plantings to control emerging weeds, organic growers rely primarily on labor-intensive hand weeding. Providing organic growers with effective supplements to hand weeding will help them become more sustainable. The cranberry industry is motivated to adopt effective pest management strategies that promote sustainability. Growers are motivated to reduce chemical inputs whenever possible because cranberries are grown in wetlands and farms are located in areas of dense suburbanization. If effective, the implementation of CGM as a preemergence weed management option could also be adopted by conventional cranberry growers who are committed to sustainability through adoption of IPM (integrated pest management) and willing to reduce chemical inputs when possible (Blake et al. 2007).

Corn gluten meal is a byproduct of wet-milling corn, and is a natural product which is approved for use in organic farming (OMRI 2012). It has been shown that CGM can provide effective weed control by inhibiting the root formation of germinating plants and affects both monocotyledonous (grasses) and dicotyledonous (broadleaf) species (Bingaman and Christians 1995; Liu and Christians 1997). It works as a preemergence herbicide with no known effect on established weeds. The use of CGM as an herbicide use was pioneered in turf management, and it has also been used in crops such as onions and strawberries, but its utility as a weed control agent has not been tested in cranberry production (Abouziena et al. 2009; Christians 2002; Dilley et al. 2002; Webber et al. 2007). This project would focus on cranberry beds that were in the “vine establishment”, which is has ample open space to allow weeds to enter the system as germinating seeds, as opposed to established beds that have mainly perennial weed species. Since CGM has a high organic nitrogen content (typically 8%), applications would also provide nutrition for establishing young vines in organic plantings as well as reduce the use of inorganic fertilizer for conventional growers who incorporate CGM into their IPM program.

This study evaluated the efficacy of CGM for preemergence weed control on young cranberry bogs based on current knowledge about CGM from studies done with turf and other crops. Two sets of experimental plots were established on an organic farm that was planted less than 3 years ago and where vines were still not adequately colonizing the surface. In the early spring of 2013, the plots were hand weeded to remove existing weeds, and then treated with a granular application of CGM. Susceptibility of weeds to CGM may vary by species (Bingaman and Christians 1995) so plots were evaluated for which weed species were present in each plot, and the relative cover of each weed. Prior to cranberry harvest, all the weeds were collected from each plot and biomasses were quantified by drying and weighing weeds by species.

The grower collaborator provided the research area on the farm, general farm maintenance, and the grower assisted with the initial establishment of the plots and was present during CGM application. The staff from the Cranberry Station was responsible for treatment applications, data collection and analysis, outreach programs, and other communications with the industry.