Weed control in low-input or organically grown wild lowbush blueberries

Project Overview

Project Type: Partnership
Funds awarded in 2014: $13,460.00
Projected End Date: 12/31/2017
Region: Northeast
State: New Hampshire
Project Leader:
Olivia Saunders
UNH Cooperative Extension

Annual Reports

Information Products


  • Fruits: berries (blueberries)
  • Additional Plants: native plants


  • Crop Production: crop rotation, organic fertilizers, tissue analysis
  • Education and Training: demonstration, extension, farmer to farmer, on-farm/ranch research, participatory research
  • Pest Management: chemical control, cultural control, integrated pest management

    Proposal abstract:

                Wild blueberries (Vaccinium angustifolium) are a crop with significant cultural and historical significance to the northeast. Demand for these culturally unique small fruits has exploded in the last ten years, especially when grown organically and marketed as such. The price of wild blueberries has risen from $0.334 in 2003 to $0.758 per pound currently. Additionally, production has risen from a low in 2004 of 46 million pounds produced, to 9.1 million pounds produced in 2012 (New England Agriculture Statistics). Management options available to low input or organic growers is limited. Specifically weed management options outside of regular burning and mowing are sparse. Little bluestem (Schizachyrium scoparius), a weed present in most production fields in western Maine and New Hampshire, can only be managed using a conventional chemical approach. With rising demand for organic fruit and conventionally managed fields being transitioned into organic production, the suite of management options for low input or organic growers must be widened.

                We will conduct a field trial to evaluate the efficacy of managing soil pH to improve weed suppression of little bluestem. Research will be replicated on two wild blueberry farms in New Hampshire using a randomized complete block design. Sulfur will be hand applied in the spring of the fruiting year to drop soil pH, and data will be collected for three years to include fruiting and non-fruiting seasons. Research will be disseminated to growers across northern New England via Extension grower events, social media, development of an Extension fact sheet, and videos.

    Project objectives from proposal:

    Typical cultural practices like burning and mowing of fields after harvest of lowbush blueberries do not provide adequate control against the weedy grass little bluestem. Growers have approached Extension looking for assistance managing this weed stating it is a large threat to the future of their business. Many have documented declining yields due to bluestem establishment. Returning to conventional management is undesirable because of concerns of ecosystem pollution from herbicide applications. Little bluestem reduces yields of wild, lowbush blueberry through direct competition for water, nutrients and sun exposure. The emergence of spotted wing drosophila as a pest issue has heightened the pressure. This weed offers a shaded environment which spotted wing drosophila tends to occupy, further exacerbating production problems.

    The lowbush blueberry crop is not planted or mechanically cultivated but managed from wild plants. Nearly all wild lowbush blueberries are grown on shallow, gravely soils on mountain sides, supported by a thin duff layer over gravel. Initially these plants are established by seed, but once established send out root rhizomes that send up new vegetative shoots above the soil surface. Optimal soil acidity level is 4.0 for blueberries, with fertilizer rates typically based on leaf tissue samples. Typically, plants respond positively to fertilizer applications, based on recommendations from leaf tissue analysis.

    Research will be conducted on two blueberry farms in New Hampshire, to evaluate the efficacy of pH management as a weed suppressing tool. Sulfur is commonly used to lower the pH of soils in blueberry production and will be used to drastically lower the pH surrounding little bluestem crowns as a natural method to suppress growth. Sulfur is easily available and its use could be a new, more cost effective and environmentally sustainable production practice to manage against weedy grasses. This approach is well suited to blueberry production because of the plants natural preference for extremely low soil pH levels.

    A randomized complete block experimental design will be used to test four treatments, low pH (4.0), medium pH (4.5), low pH (4.0) plus fertilizer, and control. While it is typically recommended to manage wild blueberries at a level of 4.5-5.0 we are trialing 4.0 as a weed management option. The preferred pH level of little bluestem is 7.0 or higher, and we hypothesize at a lower pH the weed will lose vigor due to unfavorable growing conditions. Four replications will be tested with each treatment, and plots will be 10 x 100 feet per plot. Plots will be designed in a rectangular fashion across the field to allow for the greatest amount of genetic diversity within the blueberry crop. Wild blueberry fields are populated by a random array of wild varieties. Individual plants (clones) will range from a few inches to many feet in lateral spread, therefore long, thin plots that transect a large number of these wild clones will help reduce the variability due to variety. This same experimental design will be employed at both sites. This approach was preferred by our growers because of the availability of sulfur, and the ease of integrating this technique into regular management activities.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.