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In the assessment of ecological risk posed by pesticide use, much greater emphasis has been given to the direct effects on wildlife than on impacts on wildlife habitat. Assessment of indirect effects to wildlife entails an evaluation of pesticide toxicity to plant species (and invertebrates) that make up wildlife habitats. Under the pesticide registration process in Canada and in most other countries, there is no specific requirement for testing the toxicity of pesticides to nontarget plants other than agronomically important species. The proposed nontarget plant testing guidelines summarized in this paper are intended to fill this gap. The chief objectives of the guidelines are to outline data requirements, to suggest methods and approaches for generating the data required, and to facilitate and improve hazard assessment for nontarget plants (and habitats) as a result of chemical pesticide use. The rationale behind decisions reached in the guidelines is also presented. The proposed guidelines are very flexible, as registrants may be granted a waiver for any test required, provided the rationale is justified on appropriate scientific grounds. Harmonization and comparison with other guidelines are discussed. These proposed nontarget plant testing guidelines can serve as a basis for guideline development or modernization for other jurisdictions.

Little attention has been paid, particularly in North America, to the importance of the mosaic of farmland habitats for the conservation of native plant species. We examined patterns in plant species richness, composition, and abundance at the scale of site, habitat (sites of a given habitat type pooled), and landscape for 10 farmland habitats (crop, hay field, pasture, old field, herbaceous fencerow, woody fencerow, roadside, ditch, plantation, woodlot) at 121 sites in eastern Ontario, Canada. At the site level, woodlots (3–79 ha) had the highest richness of overall (average 57.6 species), woody (23.4), and herbaceous species (25.0). Crop, herbaceous fencerow, and plantation habitats had few native species per site. Introduced species comprised>50% of herbs per site in seven habitats. Across habitats, 305 species were observed; 227 species were herbaceous, 70% of which were native and 31% of which were weeds. Wooded fencerows had the highest species richness in total (153) and for herbs (107). Woodlots had the most woody species (56). Percent native species was generally lower and percent weeds higher at the site level than at the habitat level. All habitats had unique species; woodlots had the highest number of unique species (  74). Results of the multivariate analysis for abundant herbs revealed that woodlots and plantations were different, as were crop and ditch habitats. The results of our landscape‐level study show that plant species richness and composition varied substantially among the five landscapes studied, ranging from a row‐crop monoculture landscape to a diverse mosaic of crop and noncrop habitat landscape. The row‐crop monoculture landscape had 11% of total, 4% of native, 27% of introduced, and 27% of the weed species found in the landscape with a greater diversity of crop and noncrop habitats. The richness of introduced and weed species was asymptotic with the addition of ditch, hayfield, and pasture in the landscape, and native species richness increased steeply, particularly with the addition of marsh, wooded fencerow, and woodlot. Our results emphasize the importance of maintaining a diverse mosaic of habitats and of noncrop habitats in farmland for conserving herbaceous and woody native plants.

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