Sulfur Application for Weed Specific Suppression

Final Report for FNE10-696

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
Expand All

Project Information


Soil pH was assessed in all the treatment plots at Berry Brook organic blueberry farm, and weeds were assessed and identified. Soil pH ranged from 4.6 to 5.3, with the mean pH being 5.0. This level is high when compared to what wild blueberry prefers and can withstand. By lowering the pH, blueberries can out-compete other weed species. There were no significant trends in June weed cover based on soil pH level, however the pH of 4.9 to 5.05 had more ferns than the lower or higher pH values represented. The pH range between the plots is small, so it may not be representative of a larger sample size. August weed assessments showed a trend in that goldenrod percent cover was significantly lower when pH was 4.85 or less as compared to most pH above 4.9.

Harvest data showed no significant differences in yield as a result of pH level. This was a great opportunity to calculate specific harvested yield on the property, in an area where weeds are prolific. Yield was measured as 600 pounds per acre, on average. When economics are considered, hand weeding is not an option when yield is so low. Only when the processing price is high would it be a viable option. Machine cutting weeds above the height of the blueberries makes more economical sense.


Berry Brook Organic Lowbush Blueberry Farm has major concerns with weed control and little is known about how to combat many perennial weeds that compete with the carpet of blueberries. The organic recommendation is to apply elemental Sulfur to lower the pH to a level at which the weeds can no longer out compete the blueberries. The University of Maine recommended rate is 100 lb/ac for every 0.1 pH drop desired, to a pH level as low as 4.0.

The goals of my SARE grant project are to see how different specific weeds are affected by a change in pH. By applying varying rates of 85% Sulfur to multiple replicate plots, we can measure the initial and any change in weed species present as a result of the Sulfur application. Another goal is to monitor the speed of pH adjustment, as Sulfur slowly acidifies the soil over time. Taking initial and annual soil samples, and testing pH, allows us to monitor the changes in soil acidity.

Project Objectives:
Plot Layout and starting the Study

During Spring of 2010, I set out 40 plots in 8 blocks with 5 treatments per block. I took soil samples in each plot, 20 subsamples per plot, and submitted them to the Soil Testing lab for pH evaluation. The five experimental treatments replicated in each block were: a control plot, 600 lbs S/ac, 800 lbs S/ac, 1000 lbs S/ac, and 1200 lbs S/ac. I designed a plot plan for the study as a randomized complete block design and treatments were assigned to each plot. The first 4 blocks were established in an area in which bracken and sweet ferns are the biggest weed problems, while the second set of 4 blocks were located where goldenrod is a predominant weed. I ordered Sulfur in bulk, and had it delivered to the farm and unloaded it by hand. Farm assistants helped apply the Sulfur to each plot using a hand-pushed drop fertilizer spreader. Jennifer D’appallonio assisted in weed identification and data analysis of weed cover. In the summer of 2011, I harvested all the blueberries in each of the plots, and weighed them.


Click linked name(s) to expand/collapse or show everyone's info
  • Jennifer D'Appollonio


Materials and methods:
Data Collection and Analysis

In June and August 2010, I assessed for blueberry and weed cover in 4 subsamples per plot. I used the Daubenmire rating scale, which uses percentages of plant cover in a given area, to assign a weed rating to each subsample. Weed species within each subsample were categorized and identified as: ferns, woody weeds, grasses, broadleaf weeds, and goldenrod. In June, we composed a weeding team, which consisted of 2 to 5 people. This team of weeders was timed at weeding each plot in a specific block. The first 2 blocks were weeded by 2 people, and we quickly realized it was far too much work for 2 people in the heat of the season. The second 2 blocks weeded in June were done by a group of 5 people, thereby limiting the effects of different weeders to ‘block effects.’ The weeding time was multiplied by the number of weeders, resulting in an amount of time it would take an average weeder to weed a plot (1200 square feet). This weeding will be redone during the next prune cycle to determine any decreases in weeding time based on weed control efforts. In August, the second set of blocks were weeded manually and talls weeds were cut mechanically. Times were recorded. Blocks hand-weeded in June were assessed separately from those mechanically weeded in August. Goldenrod was not assessed in the June weed assessment because goldenrod has not yet produced flowers in June, so identification compared with other asters is very difficult.

In addition to weed assessment and soil sampling, leaf tissue samples were collected from a few of the plots with no (0 lbs S/acre), medium (600 lbs S/acre), and high (1200 lbs S/acre) Sulfur inputs before the study, to serve as a representation of initial plant health. Leaf tissue analysis was done by the Analytical Lab at UMO. This information will serve as a baseline for plant health and will be sampled again after the next prune cycle when the Sulfur has begun to affect the pH.

In 2011, each plot was harvested and berry mass was recorded. Weight was taken in pounds, and mass of berries per plot ranged from 3.1 pounds to 63.4 pounds per 1200 square foot plot. I calculated the total berry mass from all the plots and determined that I harvested 600 lbs per acre of blueberry land. There was no correlation between the amount of Sulfur applied and the harvested berry mass for any of the treatment rates. There was no correlation between harvested berry mass and pH of original plots. I was not able to continue the soil sampling after that first year, and am no longer leasing the land, however, I do think a long-term study on pH effects on specific weeds should be done.

Research results and discussion:
Weed Assessment

All the collected data was entered and preliminary assessments were made. Because it could take 3 to 4 years to see any pH change due to Sulfur application, I didn’t expect to see any effects on plot pH or differences in weeds as a result of the Sulfur treatment applications the first year. This data was baseline data, but unfortunately, the study couldn’t continue as planned. I harvested each of the plots and presented them in a table much like the ones I did for weed assessment, by pH level. This data is not necessarily representative of the effect of pH on yield. None of the pH ranges had the same number of samples, and the variability was huge. There was no significant statistical difference in yields between any of the pH levels.

The results of this project showed no significant differences in weed cover as a result of the Sulfur treatment applications. I proposed assessing for ferns and goldenrod in response to changes in pH, so I did assess for both ferns and goldenrod. However, I also included other weed assessment categories: woody weeds, grasses, and broadleaf weeds, and assessed blueberry plant cover. The pH level in each plot was determined from early spring soil samples, and I correlated the types and percent of weed cover with the initial soil pH levels. The lowest pH level in any of these plots was 4.6! Most of the plots ranged in pH from 4.8 to 5.15. There were no significant trends in June weed cover based on soil pH level, however the pH of 4.9 to 5.05 had more ferns than the lower or higher pH values represented (see Figure 1). Although there are some differences, the pH ranges of the plots is minimal, so it may not be representative of a larger sample size. August weed assessments showed a trend in that goldenrod percent cover was significantly lower when pH was 4.85 or less as compared to most pH above 4.9. See attached graphs for details of all the weed assessments.
There were no significant differences in weeding time by pH level or between the treatment types. Average hand weeding times ranged from 56 minutes to 78 minutes for one person to weed one 1200 square foot plot. The average time for cutting weeds in plots with power tools ranged from 10.5 to 12 minutes per 1200 square foot plot. See attached graph for a visual representation of weeding times.

Research conclusions:
Harvest and Economics

Harvesting the fields by plot allowed me to calculate the real blueberry harvest poundage per acre. This was surprisingly higher than I was anticipating on a field in this condition. At that amount, selling to a processing facility could earn between $390 and $900 per acre at a price of $0.65 to $1.50 per acre, respectively. At about 60 minutes of hand weeding per person per plot, that comes to approximately 37 hours of hand weeding per acre. That type of weeding was definitely more thorough, but the economic return is low. At a pay rate of $8 per hour, it would cost $296 to weed an acre. Hand raking (machine raking is not an option with so many weeds) harvest would take about 8 hours per acre. Hand rakers get paid by the amount harvested, but for ease of calculations, we can assume it is the same hourly rate ($8). Therefore, the total cost of hand weeding and harvesting an acre of weedy blueberry land would come to $296 + $64= $360. With this method, net profit is only $30 per acre to $540. The price paid per pound by the processor would dictate whether a profit was made or not.

Machine weed wacking and cutting woody weeds takes about 6.2 hours per acre. At the same pay rate ($8/hr), field manager would pay an employee $49.60 or about $50 to weed an acre. The harvest cost would be the same as above ($64). Therefore, the cost per acre to weed and harvest would be about $114, with only one weeding per prune year, and not including insect control or any other management practices needed. The net profit, when machine weeding rather than hand weeding, could range from $276 to $786 per acre, other management practices not included. We would have to examine the different weeding techniques over time to determine any increase in harvest based on weeding method.

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary:

Education/outreach description:

In July, SARE and UMO co-sponsored an outreach event with MOFGA, Maine Organic Farmers and Gardeners Association, of which I was the farm host. This was one component of my outreach activities. Quite a few organic blueberry growers attended, and I was able to meet more fellow growers. I explained my proposal and how the grant process works, and everyone was very receptive to the idea of evaluating the specific weeds’ response to the change in pH. They also offered weeding suggestions such as leaving the weeds in the field once they are pulled; our weeders loaded a wheelbarrow and dumped the weeds in the woods on the edge of the field. Another facet that I discovered needs to be addressed is the issue of elemental Sulfur purity and the speed of incorporation of Sulfur based on the percent of purity. For example, does the pH drop faster when the S is 85% pure with more clay component than when the S is 99% and a rock hard pellet? I would think that the 85% would break down more rapidly, uncovering more surface area for breakdown, but this has not been examined.

Project Outcomes

Assessment of Project Approach and Areas of Further Study:

Potential Contributions


Overall, I learned a great deal from conducting this study. I do think that different weeds respond differently to slight changes in pH, and that applying Sulfur to lower pH is a good place to start with an overgrown blueberry field. I discovered that I was really harvesting about 600 pounds of blueberries per acre in these overgrown fields, and weeding them by hand was not financially feasible. Even with machine weeding, the processing price really determines whether I would be able to make any profit. And that is not even including the price of Sulfur amendment or the time taken for application.

Future Recommendations

Unfortunately, this was only preliminary data, but I hope other farmers can assess their weed types and soil pH so that we could compile a larger sample size of weed pH preference in lowbush blueberry fields. Over time, as soil pH levels change in Sulfur treated areas, it would be helpful to identify changes in the types of weeds to determine their pH preference and at what soil pH level weed types can no longer survive. This information can begin to help growers understand how pH affects weed type in their field. The study had to be terminated and weeds could not be reassessed the following prune year. Extensive and multiple weed assessments cannot be accurately performed during a crop year, as plant damage can occur from walking through developing plants.

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.