Sulfur Application for Weed Specific Suppression

Project Overview

Project Type: Farmer
Funds awarded in 2010: $5,812.00
Projected End Date: 12/31/2012
Region: Northeast
State: Maine
Project Leader:
Kristen McGovern
Berry Brook Blueberry Farm

Annual Reports


  • Fruits: berries (other)


  • Crop Production: organic fertilizers, application rate management, tissue analysis
  • Education and Training: demonstration, extension, on-farm/ranch research, workshop
  • Pest Management: weed ecology
  • Production Systems: organic agriculture
  • Soil Management: soil analysis

    Proposal summary:

    Our proposal uses a broad, recommended method of organically controlling weeds in lowbush blueberry fields and attempts to make it weed specific to save on chemical use and farmer inputs. Sulfur can be used to lower the pH of blueberry soil, which allows the blueberries to flourish while inhibiting the growth of competitive weeds. The slow effect and high cost of Sulfur additives make the recommended rate of 1000 lbs/acre to lower the pH to 4.0 difficult to attain. Many organic growers have a difficult time delivering a high quality product at a low price due to the proliferation of weeds in an organic system. By determining the necessary pH level for specific weed problems could allow growers to manage their land differently depending on the weed problem in that area. Perhaps it is not necessary to lower the pH as drastically as is recommended to control a certain weed. By examining this, we can potentially save both farmer and environmental costs and even make organic management of lowbush blueberries a more realistic goal for more landowners who depend on their land for their livelihood and for sustaining the community.

    Berry Brook is an organically certified lowbush blueberry farm in Amherst, Maine. When I began managing this 21 acre parcel, it was well overgrown with weeds and small shrubs. I have been cutting the shrubs, but the other perennial weeds are very difficult to control organically. Weed control was discussed as the biggest problem in organic lowbush blueberry production by the growers present at the Organic Blueberry Growers Meeting this past summer. The only recommendation from the University of Maine's research on organic blueberry management is to cut the perennial weeds multiple times per year and to apply Sulfur to reduce the pH of the soil. By reducing pH, blueberries can continue to thrive as they prefer a pH as low as 4.0, while the weeds cannot survive at such a low pH.

    As was discussed at the Organic Blueberry Growers Meeting, the price of Sulfur is so high that it makes it difficult for farmers to afford to apply it. In addition, it is released into the soil slowly, therefore taking a few years to reap any benefits from the application. The recommended application rate is 1000 lbs/ acre, or enough Sulfur to lower the pH of the soil to 4.0. Growers would need to do soil tests to determine the current pH and then apply 100 lbs of Sulfur per acre to lower the pH 0.1 unit. Sulfur is currently being sold for $850 per ton in Newport, Maine, which is $425 per acre at the recommended rate.

    Weeds in lowbush blueberry fields have a patchy distribution, with different species dominating various areas. For example, goldenrod is a substantial problem in the east field at Berry Brook, while sweet fern is more common in the upper west field. Goldenrod, a perennial weed complex with dozens of species native to Maine, generally prefers a pH of 4.8 or higher. By looking at specific weeds that are the predominate problem in an area, and determining the pH at which they can no longer sustain a population, growers will be able to apply only enough Sulfur to reach the optimum pH to control a particular weed problem, rather than attempting to reach a pH of 4.0 when it's not necessary. This could prevent growers from having to apply the full recommended 1000 lbs/ acre of Sulfur, eliminating both farming and environmental costs. I am seeking funds to test the amount of Sulfur that is necessary to significantly control goldenrod and sweet fern on an organic lowbush blueberry farm.

    Project objectives from proposal:

    There is much clonal genetic diversity in a lowbush blueberry field; therefore it is important to make the plots large enough to encompass more than one clone (plant). The proposed experimental design will ensure that no plot consists of only one individual clone.

    I will lay out 2 sites with 20 ft x 60 ft plots in a Randomized Complete Block Design; each site will contain a population of one of the targeted weeds covering enough area to encompass the plots. They will be staked, flagged, and numbered. Each block will consist of five plots (one of each of the four treatments or the control assigned randomly), replicated 4 times for a total of 20 plots per site/ species.

    I will begin by taking a composite soil sample (10 soil cores evenly distributed throughout the plot) from each of the plots to determine the initial pH. Then, I will apply each of the 4 treatments (Sulfur at 600 lbs/ac, 800 lbs/ ac, 1000 lbs/ac and 1200 lbs/ac) or the control (no treatment) to lower the pH. The highest rate of Sulfur application would lower the pH to the recommended 4.0. A block will be kept in the same general area of the field to eliminate effects on location of treatment plots. This will take 10 hours with 2 people.

    Sulfur will be purchased and applied with a hand spreader at the above mentioned rates in the spring (May) by me, with the assistance of my part-time farm employee. Application should take seven hours. The following amounts of Sulfur will be applied to each of the treatment plots:

    control = 0 lbs/plot
    600 lbs/ac = 16.53 lbs/plot
    800 lbs/ac = 22.04 lbs/plot
    1000 lbs/ac = 27.55 lbs/plot
    1200 lbs/ac = 33.06 lbs/plot

    Sweet fern populations will be assessed in the beginning of June, and goldenrod populations in the middle of September. These times were chosen based on the weed's emergence. Both goldenrod and sweet fern will be assessed using the Daubenmire cover scale, which is a method used to estimate percent weed cover using classes 1 – 6. The weed assessors will be taught this method by a cooperative extension blueberry specialist. Six samples per plot will be assessed using this method.

    A knowledgeable weed identifier (probably a University weed ecology student) will count the weeds in 2 blocks and I will count the weeds in the other 2 blocks. This should take 3 hours/ block / person for a total of 6 hours each at two different times in the season (June and September). This will be done again for the following two years. No pruning will be taking place on these plots for the duration of the experiment (3 years).

    Soil samples in each plot will be taken in May using the procedure recommended in the Wild Blueberry Fact Sheet #2092. Ten soil plugs 3 inch deep per plot will be taken randomly by farm worker and me, and the sample will be brought to the University of Maine soil testing lab for pH analysis. Soil sampling and delivery should take five hours with two people.

    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.