Pollinator Habitat Conservation Along Roadways, Volume 2: California (2023) / Chapter Skim
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6-1 Chapter 6 Roadside Maintenance and Vegetation Management for Pollinators 6.1 Introduction Roadside vegetation management provides a safe driving environment, preserves infrastructure, and maintains a resilient plant community. Many Departments of Transportation (DOTs)
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-2 butterfly or other needed habitat is present at a roadside site within the known range of an imperiled pollinator species, there is a chance that the pollinator is also there and that management actions could result in direct mortality. It is useful, although difficult, to survey host plants for immature stages of butterflies prior to mowing or using herbicides (or proceeding with other management actions, such as prescribed grazing)
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-3 Table 6-1. Periods of imperiled pollinator activity to avoid when conducting maintenance activities in California.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-4 Pollinator Jan Feb Mar April May June July Aug Sept Oct Nov Dec Monarch butterfly (Danaus plexippus) Overwintering habitat Valley elderberry longhorn beetle (Desmocerus californicus dimorphus)
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-5 Pollinator Jan Feb Mar April May June July Aug Sept Oct Nov Dec Hermes copper (Lycaena hermes) Wandering skipper (Panoquina errans)
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-6 Pollinator Jan Feb Mar April May June July Aug Sept Oct Nov Dec Oregon silverspot (Speyeria zerene hippolyta) Myrtle's silverspot butterfly (Speyeria zerene myrtleae)
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-7 6.3 Adjusting Maintenance Practices to Benefit Imperiled Pollinators 6.3.1 Common Roadside Vegetation Management Practices Mowing How Mowing Affects Pollinators Mowing is frequently used to maintain roadside vegetation, reduce occurrences of invasive weeds and woody plants, improve drivers' sight lines, allow vehicles to pull off, and reduce the risk of wildfires. Typically, vegetation in the recovery area (also known as the clear zone -- the band of vegetation directly adjacent to the pavement or shoulder where vehicles that have left the roadway can recover)
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-8 2003; Noordijk et al.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-9 throughout the growing season. Furthermore, a mowing event in the fall can help spread wildflower seeds.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-10 See Chapter 3 for natural history information for imperiled species and Table 6-1 for adult flight times and breeding seasons of imperiled species in the region. Adjust mowing height to a minimum height of 8 to 10 inches in areas with target butterfly host plants or bumble bee colonies in grass thatch, if mowing during the growing season.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-11 postponing mowing until after first frost in the fall would allow flowering plants to bloom and provide the bees with pollen and nectar throughout their flight season (i.e., late spring until early fall)
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-12 Box 6-3. How Do Other Wildlife Respond to Maintenance Practices Designed to Help Pollinators?
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-13 Box 6-4. Communicating Mowing Guidelines to the Staff One challenge when implementing changes to maintenance practices such as mowing schedules is communicating those changes to the staff.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-14 The indirect effects of herbicide use that reduces or eliminates host plants or flowering plants that provide pollen and nectar are more likely to have greater adverse impacts on imperiled pollinators than direct toxicity. Herbicides are designed to kill plants; they are not intended to kill insects.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-15 Table 6-2. Herbicides used on roadsides and what is known of their potential direct toxicity to pollinators.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-16 Herbicide Ratinga Precautions for Use within Roadside Pollinator Habitatb Source Dicamba Moderately toxic to adult honey bees Do not apply to or allow to drift onto flowers in bloom (including weeds) AERU 2022 Dichlobenil Moderately toxic to adult honey bees Do not apply to or allow to drift onto flowers in bloom (including weeds)
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From page 161... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-17 Herbicide Ratinga Precautions for Use within Roadside Pollinator Habitatb Source Fosamine Practically non‐toxic to honey bees No bee precaution, except when required by the label or regulations AERU 2022 Glyphosate Moderately toxic to honey bee adults and their brood, with impacts on gut biota, navigation, and survival Do not apply to or allow to drift onto flowers in bloom (including weeds) University of California Statewide Integrated Pest Management Program 2022 Motta et al. 2018, 2020 Battisti et al. 2021 Halosulfuron‐methyl Practically non‐toxic to honey bees No bee precaution, except when required by the label or regulations AERU 2022 Imazapic Practically non‐toxic to honey bees No bee precaution, except when required by the label or regulations AERU 2022 Imazapyr Moderately toxic to honey bees upon ingestion Practically non‐toxic upon contact Toxic to butterflies exposed as larvae, including some imperiled species Do not apply to or allow to drift onto flowers in bloom (including weeds)
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-18 Herbicide Ratinga Precautions for Use within Roadside Pollinator Habitatb Source Metsulfuron‐Methyl Moderately toxic to honey bees Do not apply to or allow to drift onto flowers in bloom (including weeds) AERU 2022 Norflurazon Practically non‐toxic to honey bees No bee precaution, except when required by the label or regulations University of California Statewide Integrated Pest Management Program 2022 AERU 2022 Oryzalin Moderately toxic to honey bees Do not apply to or allow to drift onto flowers in bloom (including weeds)
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-19 Herbicide Ratinga Precautions for Use within Roadside Pollinator Habitatb Source Pyraflufen Practically non‐toxic to moderately toxic to honey bees Do not apply to or allow to drift onto flowers in bloom (including weeds) University of California Statewide Integrated Pest Management Program 2022 EFSA 2015 Rimsulfuron Moderately toxic to honey bees upon ingestion Practically non‐toxic upon contact Do not apply to or allow to drift onto flowers in bloom (including weeds)
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-20 Herbicide Ratinga Precautions for Use within Roadside Pollinator Habitatb Source Triclopyr Practically non‐toxic to honey bees Toxic to butterflies exposed as larvae, including some imperiled species Avoid regular/repeated use on flowering plants Make applications outside season when caterpillars are active (see Chapter 3 for adult and larval active periods by species) EPA 2017 Stark et al. 2012 a. The data are incomplete because of limitations on herbicide testing on terrestrial insects. Toxicity ratings are based primarily on acute contact toxicity testing conducted on adult honey bees as part of the EPA pesticide registration process. Adult honey bees (Apis mellifera)
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-21 Adjusting Herbicides to Support Imperiled Pollinators Best herbicide practices for imperiled pollinators include reducing herbicide exposure as much as possible when working in their habitat. Employ a variety of vegetation management techniques, including cultural and mechanical control.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-22 reduce unnecessary effects on desirable plants. Use broadcast treatments or pellet dispersal only for dense infestations of weeds, the safety zone, and guardrail treatments.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-23 Butterfly and moth caterpillars consume host plant vegetation over days to weeks; residues in host plant vegetation could account for the bulk of exposure over the life cycle of these species. Larval butterflies and moths could be chronically exposed to systemic herbicides that are taken up by host plants or the residues of persistent herbicides, which take weeks to dissipate in the environment and have detrimental sublethal effects (Olaya-Arenas et al.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-24 and larvae are active in this region and Table 6-2 for a list of herbicides with high toxicity to pollinators. If treatment cannot be scheduled outside the window when pollinators are present, consider a mechanical control strategy when feasible if in an area where herbicide use might affect imperiled species.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-25 Box 6‐7. Adjusting Herbicide Practices to Support Monarch Butterflies One of the most iconic pollinator species, the monarch butterfly (Danaus plexippus) , is recognized and celebrated by people throughout North America.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-26 Conservation actions that support pollinators generally include: Feather or soften forest edges adjacent to the recovery area to create a transitional area between forests and grass (e.g., thin portions of the forest canopy along the edge next to grassy areas, removing undesirable or unhealthy trees)
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-27 Box 6-8. Current Brush Removal Practices by DOTs Most respondents reported using practices that minimize soil disturbance during brush removal.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-28 season. Haying is not a tool that is typically used by a roadside maintenance staff, although there may be advantages to haying for vegetation management for DOTs to consider for future usage.
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From page 173... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-29 Prescribed Grazing Grazing is used to limit tree and shrub invasion, provide structural diversity, and encourage the growth of nectar-rich plants. However, livestock grazing is beneficial to plant diversity, and, in turn, pollinators, at only low to moderate levels during short periods, which are separated by long periods of recovery (Hopwood et al.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-30 but it can have long-term effects on the populations of some species when refuges from burns are not available (Ne'eman et al.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-31 Prescribed grazing: Graze during peak growth of target weeds; if grazing for diversity, keep stocking rate low and rotate 6.3.4 Road Salts and Heavy Metals Routine vehicle use and road maintenance contribute to roadside vegetation contamination by depositing pollutants, including vehicle exhaust and de-icing materials. Vehicle-derived heavy metal contamination in roadside soils and vegetation is proportional to traffic levels (Leharne et al.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-32 6.3.5 Signage Signage can be used to help the maintenance staff identify areas that need particular management techniques or understand the timing of management that is unique to a particular site. The use of signs during maintenance may help the staff recognize sites with known populations of listed or imperiled pollinators, which may require specialized maintenance.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-33 adjacent to the roadway, the goal was to leave more vegetation that could be used by monarchs. Mowing is still used when needed beyond the 15-foot zone to control the spread of invasive species and maintain sight lines for driver safety.
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From page 178... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-34 Mapping and planning are key elements of WSDOT's approach to roadside revegetation and maintenance. Vegetation inventories help identify areas with weed infestations as well as areas that are conducive to managed succession.
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From page 179... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-35 County is also working to restore upland prairie at a mitigation site to provide habitat for these protected species. Yamhill County's Habitat Conservation Plan is found here: https://www.fws.gov/oregonfwo/documents/hcp/YamhillHCP_Final.pdf.
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