Grit Weeding to Efficiently Control Weeds in Raspberries

Steve Poppe WCROC Horticulture Scientist, Mary Rogers Assistant Professor and Andy Petran Postdoctoral Associate, U of MN Department of Horticultural Science

Raspberries are an increasingly valuable horticultural crop in the United States. The US is the world’s 3rd largest raspberry producer, with acreage, price/lb and total sales increasing to a value of approximately $581 million in 2015. The majority of production takes place in California, Oregon and Washington, but local raspberry growers can be found throughout the US, employing a diversity of cultural practices that reflect the diversity of environments they are grown in. Despite the prevalence of national production, there is a scarcity of published research on weed control in raspberry and other bramble crops- especially within-row weed control, which is challenging for all producers. Studies have shown that within-row weeds have a negative effect on cane growth and mortality. The little research that is available focuses mainly on herbicide-based management. While herbicidal management can be effective, there are concerns about cost and environmental effects. Organic growers cannot use most herbicides, and sprays are not recommended for new plantings, when canes are most vulnerable to weed pressure. Thus organic growers are typically forced to rely on manual within-row weeding, which is time consuming, labor intensive, and expensive.

Grit blasterDevelopment of best practices for organic, within-row weed management of horticultural crops (both annual and perennial) is necessary for improving yields, profitability and reducing barriers to adoption. To address these issues we are investigate grit weeding as an alternative weed management strategy in organic, fall-bearing raspberry production at WCROC. Grit weeding is a practice in which a soft, abrasive substrate, typically an agricultural residue such as corn cob grit or rice husks, are propelled via compressed air towards weed seedlings for within-row weed control. Grit weeders can be cheaply produced by modifying a sandblasting device or pressure washer to be pulled by a small tractor. Since the practice utilizes decomposable agricultural waste it is cost-effective and can be used on organic systems. Grit weeding has demonstrated effective and selective weed control in corn, soybean, tomatoes and peppers without affecting yields. Unlike herbicidal management, grit weeding may have the potential to be used on new fruit and vegetable plantings.

The rate and frequency of grit application for effective weed control has been investigated, but never applied for use in perennial fruits. Before grit weeding can be recommended for organic horticultural production systems, we must investigate its effect on plant growth and development. If successful, integrating grit weeding into raspberry production may create systems that are more efficient and cost-effective than traditional practices, especially for organic growers who rely on manual weeding for within-row management.

Funded by the North American Bramble Growers Research Foundation