Early adopters of impact mills
A survey of early adopters of physical impact mills found that wild oat (60%) and kochia (50%) were the weeds most frequently mentioned as specific motivators for impact mill purchase. Average increased fuel cost for a mill was estimated at $1.40/ac, with average annual maintenance costs of about $1,500 per impact mill. Sixty per cent felt the average payback time would be in 3 to 5 years.
Harvest weed seed control (HWSC) is a tool to help reduce the return of seeds to the soil seedbank at harvest. These tools include chaff carts, direct bale systems, narrow-windrow burning, chaff lining or tramlining, and physical impact mills. In Canada, HWSC research has focused on impact mills as the most likely adopted system on the Prairies.
Three integrated impact mills are on the market, and include the iHSD (integrated Harrington Seed Destructor) from De Bruin Engineering, South Australia, the Seed Terminator from South Australia, and the Seed Control Unit from Redekop Manufacturing, Saskatchewan.
The adoption of physical impact mills has seen some inroads on the Prairies with an estimated 30 impact mills in use in western Canada in the fall of 2023. Understanding producer experiences with impact mills helps to identify knowledge gaps such as average fuel and maintenance costs, and provide direction for future research.
The objective of this study was to gain insight from early adopters on the Prairies to remove barriers to adoption and identify research and extension needs – ultimately to increase the adoption of HWSC as part of an integrated weed management program in Canada.
A 49 question survey was developed, and circulated to early adopters of impact mills on the Prairies. Ten producers responded to the survey, with a total of 18 mills on these farms. This accounted for 18 out of an estimated 30 impact mills in use primarily on the Prairies. Two mills were used in Alberta and the rest in Saskatchewan.
One to 4 combines were equipped with mills on the farms, and the number of combines equipped with a mill averaged 75%. On farms where mills were not installed on all the combines, the producers indicated the mills were used in weedy areas, patches, and areas such as headlands that are prone to higher weed densities.
Forty per cent of the mills were used on farms greater than 10,000 acres (>4047 ha), and the mills were used in all their crops grown. This was likely due to the high capital cost of the mills, as well as the need for Class 8 or larger combines to drive the mills..
Motivation for HWSC varied
The most common weed that motivated the purchase of a mill was wild oat at 60% of respondents. This was likely because wild oat remains in the top five weeds in Prairie weed surveys, as well as being one of the most common herbicide-resistant weeds. This was surprising because previous research found that wild oat was a poor candidate for HWSC because of early seed shed and poor retention of seed at harvest.
Wild oat was followed by kochia at 50%, wild mustard at 30%, and sow thistle, cleavers and volunteer crops at 10%. Additionally, 30% of producers indicated that all weeds were the motivation behind their purchase of impact mills.
The three primary goals behind adopting impact mills were reducing/managing the weed seed bank at 40% of respondents, managing current and future herbicide resistance at 50%, and reducing weed densities mentioned by 40% of respondents. Other comments included the reduction of chemical use, and reducing weed density prior to establishment of site-specific application technology.
The three earliest adopters, one in 2018 and two in 2020, reported an estimated reduction in weed densities by 75%, 50% and 60%, respectively, for an average reduction of 62%. Kochia was most often mentioned, but some commented that grass herbicide applications could also be reduced.
Two respondents indicated their herbicide applications were reduced by 25 and 30% in the first 3 to 5 years of use.
Patch management was also seen as a benefit by some respondents. Kochia and wild oat were both mentioned as problem weeds that had not spread in the field when mills were utilized. This provided the opportunity to target wild oat and kochia patches with residual herbicides.
Increased fuel consumption was estimated to be $1.40/ac ($3.46/ha) ranging from $0.50 to $2/ac ($1.24 to $4.94/ha). Annual maintenance costs averaged $1,500 per mill, but ranged from $0 to $5000.
Respondents estimates of increased fuel costs and annual maintenance costs of an impact mill
Source: Tidemann et al. 2024
Six respondents felt that the impact mill would pay for itself in 3 to 5 years. Two felt the payback was in 6 to 8 years, 1 respondent thought in 1 to 2 years, and another in more than 10 years. The payback would come from reduced weed densities, reduced weed spread, and reduced herbicide application requirements.
Some limitations
The biggest limitation was the plugging of the mill with green material, cited by 70% of respondents. The need for swathing, desiccation or avoiding green patches during harvest were suggested as options to overcome this limitation. Later maturing kochia was noted as particularly problematic.
Seventy per cent of the respondents brought up the horsepower draw of the mills, which needed to be balanced off with reduced speed and combine efficiency.
Research needs identified were long-term monitoring of efficacy on weed densities and differences by species, the interaction of HWSC and precision spraying technologies, effect of adding an impact mill to combine operation and grain losses in return elevators and augers, and combine efficiency.
Several respondents summarized their thoughts:
- “the impossibility of 100% control due to seed shatter prior to harvest, header losses, etc.”
- “Don’t expect instant results”.
- “Adopt now and protect herbicide modes of action before [it’s] too late”.
Finally, the need to couple extension events with research and on-farm experiences was identified as a way to encourage adoption of HWSC.
The authors are grateful for the support of the Public Opinion Research group of Agriculture and Agri-Food Canada for their assistance in setting up the survey, in particular S. McLellan. We also appreciate the efforts of the mill manufacturers and distributors to get the survey link out to their customers. This research received no specific grant from any funding agency, commercial or not-for-profit sectors.
Dr. Breanne D Tidemann, Dr. Charles M. Geddes, and Dr. Shaun M. Sharpe. Early adopter insights on physical impact mill technology for harvest weed seed control in Canada. Canadian Journal of Plant Science. OPEN ACCESS https://doi.org/10.1139/cjps-2024-0015
