Survey of weed management needs in Oregon mint production

Oregon is one of the leading U.S. states for peppermint (Mentha × piperita L.) and spearmint (Mentha spicata L.) production, accounting for 30 and 22% of the nation’s output, respectively (ODA, 2024). In 2024, more than 8,000 ac of peppermint and spearmint were harvested across Oregon, yielding over 1.6 million lb of oil (Oregon Mint Assessment Report, 2025). Weeds represent a major challenge to mint production, reducing both crop biomass and oil quality. Understanding current weed management challenges, as well as the resource and information needs of stakeholders, is critical for guiding research, extension, and education efforts for effective weed management. To support this effort, a statewide weed management needs assessment survey was conducted in 2025 to identify key challenges and priorities among Oregon’s mint stakeholders.

Needs assessment survey

The survey was made available online through the Qualtrics platform from December 2024 to April 2025. A survey link was distributed via email to the Oregon Mint Commission. Additionally, it was shared on LinkedIn and Twitter, and a QR code linking to the survey was shared during the Oregon Mint Growers Meeting. Extension agents and crop consultants also assisted in distributing the survey. 

The survey consisted of 25 questions organized into four sections: Section 1: general information; Section 2: weed management challenges; Section 3: current weed management practices; and Section 4: weed management research and extension priorities.

Survey responses

Section 1: General information

The survey had 32 respondents, most of whom were growers (47%) or crop consultants (34%) (Table 1). The majority reported farming or consulting in Benton, Linn, Marion, and Jefferson counties (Figure 1). Sixty-three percent of respondents grow peppermint while 38% grow both peppermint and spearmint. When asked about their experience growing mint, the largest proportion of respondents (39%) reported more than 20 years of experience. Over 70% of respondents farm or consult between 100 and 500 ac (Table 1).

Section 2: Weed management challenges

Respondents reported difficulty controlling several weed species using multiple herbicides. Among the grass species, annual ryegrass, barnyardgrass, Italian ryegrass, and reed canary grass were listed as the most difficult to control; each was associated with at least three different herbicides. For broadleaf weeds, common groundsel was the most frequently reported with poor control associated with seven distinct herbicides. Other broadleaf weeds reported as difficult to control included Canada thistle, prickly lettuce, pigweeds, and wild mustard; each was associated with at least three different herbicides (Table 2).
 

According to respondents, weeds pose the greatest challenge during the crop’s active growth stage with 54% identifying this period as the most problematic. In terms of specific weed management challenges, herbicide resistance was reported by 67% of respondents, followed by limited herbicide options (63%) and herbicide application timing (58%) (Table 2).

To better understand the economic impact of weed management in mint production, respondents were asked about their average weed control costs per acre. Thirty percent reported spending between $100 and $150 per acre, 26% indicated costs of $150 to $200 per acre, and another 26% reported spending more than $200 per acre. Additionally, 13% spent between $50 and $100 per acre while 4% indicated costs ranging from $10 to $50 per acre (Table 2).

Respondents were also asked a series of questions related to herbicide resistance, including their level of concern, experiences with herbicide failure or reduced efficacy, observations of resistant weeds, and the management strategies they implemented to address herbicide resistance. A majority (63%) reported being very concerned about herbicide resistance, 33% were somewhat concerned, and only 4% expressed no concern. When asked about their experiences, 67% indicated they had encountered herbicide failure or reduced efficacy, 21% had not, and 13% were unsure. Additionally, 70% reported observing herbicide-resistant weeds while 30% had not. Reported cases involved grasses such as annual bluegrass, downy brome, and foxtail species, primarily associated with resistance to clethodim and terbacil. Broadleaf weed cases included common groundsel and pigweed species associated with resistance to bromoxynil and sulfentrazone, respectively (Table 2).

To address herbicide resistance, respondents reported implementing a range of management strategies (Table 2). The use of pre-emergence herbicides was the most common (79%), followed by rotating herbicide modes of action (75%), and tank-mixing herbicides with multiple modes of action (71%). Adoption of both cultural and mechanical weed control practices was reported by 50% of respondents for each. Additionally, when asked how environmental concerns influence their weed management decisions, 33% of respondents indicated a strong influence, 50% reported some influence, and 17% stated no influence (Table 2).

Section 3: Current weed management practices

Survey respondents were asked about their current weed management practices, including type of harvest, methods of weed control, perceived effectiveness of these practices, herbicide use (e.g., pre-plant burndown, pre-emergence, and post-emergence), and frequency of herbicide applications during the growing season. Most respondents reported using single-cut (64%) over double-cut harvest (36%) (Table 3). Chemical control was by far the most commonly used weed management method, cited by 64% of the respondents, followed by cultural (18%) and mechanical practices (14%). Regarding the effectiveness of their weed management practices, 77% of respondents considered them somewhat effective while 23% rated them as very effective. 

In terms of herbicide use, paraquat, glyphosate, and oxyfluorfen were the most frequently used for pre-plant burndown (Table 3). For pre-emergence weed control, the most common herbicides were terbacil, oxyfluorfen, and sulfentrazone. Post-emergence applications primarily included clopyralid, bentazon, and terbacil. When asked how often they apply herbicides during a growing season, most respondents (73%) reported applying herbicides two to three times while smaller proportions reported applying them once (9%), four to five times (9%), or more than five times (9%).

Section 4: Weed management research and extension priorities

Survey participants identified key research and extension priorities for improving weed management in Oregon mint production (Table 4). The most frequently selected topics for additional information or training were herbicide efficacy and application timing, and herbicide resistance, each chosen by 68% of respondents. Weed biology and ecology were selected by 37% of respondents and non-chemical weed control methods by 26%. Regarding preferred formats for receiving weed management information, 90% of respondents favored field days, followed by workshops (70%), webinars and online courses (40%), and website posts (35%). An additional 10% selected “other” formats, including the Pacific Northwest Weed Management Handbook. Respondents also outlined future research and extension needs or expectations for the Extension Weed Specialist at Oregon State University. These included topics such as new herbicide chemistries and modes of action, optimal tank mixes and application timing, and the economics of herbicide resistance management practices, among others (Table 4).

Implications for future research and outreach

The results of this survey provide valuable insights into the current weed management challenges faced by Oregon mint growers and will help guide future research and extension efforts. By aligning research priorities with growers’ needs, these findings can support the development of practical, science-based strategies tailored to the unique demands of mint production in the state.

References

ODA. (2024). Oregon agricultural statistics. Oregon Department of Agriculture. https://www.oregon.gov/oda/Documents/Publications/Administration/ORAgFactsFigures.pdf