EPPO Global Database

EPPO Reporting Service no. 08 - 2007 Num. article: 2007/161

Preventing introductions of invasive plants for horticultural purposes through voluntary initiatives in the USA

Although prevention is the most cost-effective way to avoid plant invasions, the scientific community, the public sector and private institutions have dedicated substantially more attention and resources to eradication and control. Consequently, invasive plants continue to be freely imported and commercialized for horticultural purposes. In the USA, the horticultural trade, which is economically important and one of the fastest growing segments of agriculture, is considered to be the main pathway for introducing invasive plants. With very little government regulation on imports of invasive plants, efforts are currently being made to encourage self-regulation of the horticultural trade through voluntary initiatives. It is considered that self-regulation is likely to reduce the introduction of invasive plants as:
- it deals with non-essential commodities, in both ornamental landscaping and erosion control, non-invasive alternative plants can be substituted for invasive plant
- close consumer contact and high public visibility of the horticultural trade can help to build an environmentally responsible business image and generate more profits
- the threat of increased government regulation of horticultural imports is presumed to encourage the horticulture trade to proactively adopt voluntary initiatives.
In order to assess the potential efficacy of such voluntary programmes, it is important to identify the social factors that will affect the participation of the horticultural industry. A survey of wholesale and retail nurseries was conducted in California in the San Francisco Bay area to gauge the nurserymen’s perception of the invasive species, the role of the horticultural trade in invasive plant introductions, and their participation – potential or actual – in preventive measures (outlined in the St Louis Voluntary Codes of Conduct for nurserymen, see EPPO RS 2007/081). Forty-five nurseries out of 207 responded to the telephone survey consisting of 25 questions. As the region studied has a reputation for environmental activism, it was anticipated that these results would be superior to the national average.

Perspectives on invasive plants and involvement in prevention
Results show that awareness of the invasive plant problem among professionals was high. All survey respondents (100%) had heard the term “invasive species”. An overwhelming majority (93%) agreed that “invasive plants are an important environmental concern”. Most respondents (82%) agreed that “the horticulture trade has a role in the introduction of invasive plants”.
Furthermore, respondents indicated that horticultural groups were more “responsible for preventing plant invasions via the horticulture trade” (growers, wholesalers, retailers, by order of highest responsibility score) than non-horticultural groups (scientists, policy makers, government agencies, consumers, by order of highest responsibility score).
Very few respondents knew of the St Louis Voluntary Codes of Conduct. About 83% of respondents reported having participated in at least one preventive measure, whereas nearly all (98%) respondents reported that they were at least willing to participate in one or more measures. The percentages of respondents reporting that they “have engaged” or “would engage” in specific preventive measures are presented below:

Preventive measures
% of respondents reporting “have engaged”
% respondents reporting “would engage”
Evaluate horticultural plants for whether they are likely to become invasive
Monitor plants to assess whether they may be invasive
Interact with experts to determine which plants are or might become invasive
Try to breed alternatives to invasive plants
Phase out plants that nursery associations, scientists and other experts determine to be invasive
Encourage customers to use non-invasive plants

Approximately half (52%) of the respondents indicated that learning of the existence of the St Louis Voluntary Codes of Conduct during the survey made them more likely to participate in the preventive measures outlined in this initiative. While participation in preventive measures is not currently widespread, the survey indicates potential for improved future participation.

Relating perceptions, business characteristics and preventive behaviour
Respondents with a higher awareness of the invasive plant problem reported significantly greater participation in preventive measures. Respondents who reported greater involvement with trade associations reported participating in significantly more preventive measures. An explanation could be that nurserymen involved in trade associations may identify more closely with the nursery community and share greater awareness of current issues in horticulture, perhaps via information directly disseminated by these trade associations. Nursery type (retail versus wholesale) and size were non-significant predictors of participation in preventive measures, and business size and visibility to consumers were not found to influence decisions as much as personal motivation.

Incentives and obstacles
Incentives and obstacles to participation in preventive measures are reported below, ranked by percentage of respondents:

% cited

Concern for the environment
Cultivating a green business image
Consumer demand
If other nurseries were doing these activities
Employee pressure
Preventing government regulations

Lack of information
Limited personnel
Too time-consuming
Too expensive
Lack of incentive
Other environmental concerns are more important
Lack of interest
Engaging in those activities will not help to prevent invasions
Other nurseries are not doing these activities

These results highlight that cited incentives rank in an order that emphasizes a strong environmental ideology and de-emphasizes purely business-related incentives. Nurserymen in the region under study claim a strong environmental ideology as a significant motivator to their actions. Similarly, all top-cited obstacles pertained to feasibility of participation, while respondents least cited belief-related obstacles. Respondents most often cited “lack of information” as an obstacle to participation in preventive measures. Necessary information may include species-specific evaluations of invasiveness, practical guidelines for implementing preventing measures, proposals for alternatives.

In general, the survey results are promising in terms of voluntary self-regulation of the horticultural trade. Whether the nurserymen will participate to the extent required to effectively prevent introductions of horticultural invasive species will depend on whether the identified obstacles, notably the lack of information, can be overcome. It will also depend on the motivation of individual nursery practitioners, some of whom refused to participate in the majority of preventive measures. Success at a broader scale may be compromised if the intended goals of voluntary codes of conduct cannot be achieved in this particular population of nurserymen. Since information circulating through trade associations may not reach most nurserymen, popular horticultural references may be a promising means of communication. Incorporating an invasiveness rating in such references could become an effective means of preventing sales and spread of invasive plants at all levels, from commercial nurseries to the individual consumer.


Burt JW, Muir AA, Piovia-Scott J, Veblen KE, Chang AL, Grossman JD, Weiskel HW (2007) Preventing horticultural introductions of invasive plants: potential efficacy of voluntary initiatives. Biological invasions. DOI 10.10007/s10530-007-9090-4. http://www.cpb.ucdavis.edu/bioinv/downloads/Burt_etal_2007_Biol_Inv.pdf