Pollinator Refuge Establishment and Conservation Value: Impacts of Seedbed Preparations, Seed Mixtures, and Herbicides

On-farm pollinator refuge habitats can supplement floral and nesting resources to support wild and managed pollinator communities. Although the popularity of installing these habitats has grown, and federal programs provide technical and financial advice to participating landowners, recommendations regarding habitat establishment and species composition vary. We examined the effects of seedbed preparation, seed mix composition, and herbicide applications on pollinator refuge establishment and pollinator visitation in a controlled experiment across 2 years. Seedbeds were prepared either by a no-till method with glyphosate herbicide or by repeated conventional inversion tillage. Seed mixes contained either nine annual, biennial, and perennial forbs (mix AP); seven annual, biennial, and perennial forbs that are tolerant to imazapic herbicide (mix IT); or nine perennial forbs (mix P). Mixes AP and P were grown with and without application of the graminicide herbicide sethoxydim and mix IT was grown with application of the herbicide imazapic. Seedbed preparation methodology had a strong impact on pollinator refuge establishment. A no-till approach generated greater wildflower and lower weed cover relative to tillage, leading to a greater number of blooms. In particular, there were more Indian blanket, purple coneflower, slender mountain mint, and wild bergamot blooms following a no-till seedbed preparation, indicating that certain species are more vulnerable to the effects of tillage than others. The AP and IT treatments displayed more wildflower and less weed percent cover than the P treatments during the first year, but in the second year wildflower and weed cover were similar across all mixes grown with and without herbicide. Overall pollinator abundance, which was dominated by native bees, correlated positively with wildflower bloom counts, suggesting that habitat establishment methods that increase wildflower blooms can positively affect the pollinator conservation value of the habitats. This research indicates that establishing on-farm wildflower habitats can be most successful with no-till seedbed preparation, a mixture of annual, biennial, and perennial forb species, and that herbicides applied after planting wildflowers may not be worth the costs of application.