Pollinator Habitat Conservation Along Roadways, Volume 4: Great Basin (2023) / Chapter Skim
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Pages 97-130
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From page 97... ...
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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From page 98... ...
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 the Great Basin.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-4 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 6-5 2003; Noordijk et al.
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Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-6 plants will be able to bloom and provide pollen and nectar to pollinators uninterrupted throughout the growing season. Furthermore, a mowing event in the fall can help spread wildflower seeds.
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From page 103... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-7 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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From page 104... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-8 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 6-9 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 6-10 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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From page 107... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-11 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 6-12 Table 6-2. Herbicides used on roadsides and what is known of their potential direct toxicity to pollinators.
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From page 109... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-13 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 110... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-14 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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From page 111... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-15 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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From page 112... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-16 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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From page 113... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-17 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.
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From page 114... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-18 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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From page 115... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-19 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 6-20 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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From page 117... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-21 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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From page 118... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-22 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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From page 119... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-23 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 6-24 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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From page 121... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-25 or allow annual haying by adjacent landowners on certain roads throughout the growing 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 122... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-26 nontarget native species, is important in evaluating the potential effects of biocontrol agents. Prescribed Grazing Grazing is used to limit tree and shrub invasion, provide structural diversity, and encourage the growth of nectar-rich plants.
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From page 123... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-27 Prescribed Fire Prescribed fire is used to manage roadside vegetation and rejuvenate plant diversity in some regions of the United States that have a history of natural fires. Prescribed fire can remove old vegetation to create room for new growth, can reduce the spread of some invasive plants, and can stimulate the seed germination of some wildflowers.
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From page 124... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-28 guidance on the general timing of vegetation maintenance practices that best encourage plant diversity in this region. However, it is important to note that the timing can be in direct conflict with the activity of certain imperiled pollinator species.
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From page 125... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-29 Until widespread data are available, DOTs that use road salts frequently in areas with high-traffic levels may consider increasing the width of the mown strip in the recovery area. (Plants are more likely to be toxic when traffic levels exceed 20,000 cars per day.)
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From page 126... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-30 6.4 Case Studies 6.4.1 Adjusting Mowing Practices to Benefit Monarch Butterflies in Illinois The monarch butterfly (Danaus plexippus) is the official state insect of Illinois.
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From page 127... ...
6-31 Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators reduced mowing and targeted herbicide use. Managed succession allows native vegetation to emerge and flourish, with sagebrush (Artemisia tridentata)
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From page 128... ...
Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators 6-32 foreslope had negative impacts on Fender's blue butterfly and Kincaid's lupine. Under these conditions, it became appropriate to reduce the attractiveness of the foreslope to Fender's blue butterfly by managing it so that Kincaid's lupine would not persist.
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From page 129... ...
6-33 Chapter 6. Roadside Maintenance and Vegetation Management for Pollinators Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies: https://www.nap.edu/catalog/25693/evaluating-the-suitability-of-roadway-corridors-for-use-by-monarchbutterflies and http://www.trb.org/Main/Blurbs/180186.aspx.
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