Restoration of Rare or Declining Natural Communities

Conservation Practice 643 – Beetle Bank Specification

Figure 1. Beetle bank (photo courtesy of Gwendolyn Ellen, Oregon State University, Integrated Plant Protection Center).

Definition

A beetle bank is a mounded berm, densely-planted to grasses that is installed to replace missingresting and overwintering habitat for beetles, spiders and other beneficial insects that attack crop pests in crop fields.

PURPOSE

To provide a relatively dry area of undisturbed and untilled ground within annually tilled crop fields where beneficial insects can be protected from tillage and pesticide applications.

CONDITIONS WHERE PRACTICE APPLIES

This practice applies to all annually tilled fields, where regular disturbance results in the loss of overwintering or resting habitat for beetles, spiders and other beneficial insects.

WHAT IS A BEETLE BANK?

Beetle banks are habitat enhancements that provide shelter for predatory ground beetles and other beneficial insects. Beetle banks consist of long, elevated earthen berms planted with perennial bunch grasses (and sometimes combined with a low density of native wildflowers). The banks provide winter cover for ground beetles and other beneficial insects adjacent to or within cultivated fields, and are intended to promote rapid movement by beneficial insects into crop fields when warm weather returns in the spring.

The beetle bank practice originated in Europe to provide habitat for beetles, spiders, and other beneficial insects that declined because of the loss of hedgerows and other natural habitat adjacent to croplands. British farmers have used the beetle bank concept to successfully control grain crop pests like aphids and wheat blossom midges – in some cases eliminating the need for pesticides. Additional research indicates that various ground beetle species supported by beetle banks may feed extensively on weed seed, and may play an important role in suppressing crop weeds. Despite these promising results, beetle banks remain largely untested in the United States.

DESIGN AND CONSTRUCTION

Beetle banks are usually constructed by plowing two reverse furrows side-by-side to create an embankment that is 2ft to 6ft wide and at least 1ft high. To maximize ease of grass establishment, the embankment is created in the fall (latest in the spring), and germinating weeds are eliminated during the growing season through regular herbicide, flame weeding, or other weed control techniques. The goal is to dramatically reduce cool and warm season weed pressure. In the next fall, the bank is then seeded with native bunchgrasses or transplanted with native bunchgrass plugs. It is important that the chosen grasses produce dense clumpsthat provide overwintering cover for the beneficial insects.See Tables 1 and 2 for cool-season grass species recommendations and planting specifications.We recommend including at least three species to help ensure successful establishment.

If seeding a beetle bank, lightly rake after broadcasting the seed and use a lawn roller, cultipacker, or other tool to press seed into the mound to maximize seed-soil contact.Sow seed between Sep 1 and Oct 15 to have seed in the ground that is able to germinate and establish with first rains. On east side of Cascades, seed can be planted in late August if irrigation is available before fall rain starts. If planting plugs, wait until first rains have started, unless you are able to irrigate. Note that if weed pressure in the field is very low, beetle banks can be planted with plugs and heavily mulched immediately after mounding in the fall.

Native flowering perennials can be added to beetle banks to increase the services provided by the banks, supplying pollen and nectar for native bees and other beneficial insects. It is best to add the flowering species in sections separate from the grasses as their maintenance is different.

Beetle banks are often positioned in the center of crop fields and extend almost to the field edges, allowing enough room on each end for equipment to pass without damaging the berm. In this way, the entire field around the beetle bank can be cultivated and the bank will be positioned such that beetles can disperse into crops in all directions. Large crop fields may require multiple beetle banks positioned at regular intervals to account for the dispersal distance limits of ground beetles and other beneficial insects. Current guidelines in Britain recommend at least one beetle bank per 50 acres, ideally placed in the center of the field. If planning multiple beetle banks, you can consider placing them at approximately 200 ft intervals, a recommendation based on estimated dispersal distance of ground beetles and other beneficial insects.

Table 1. Native cool season grass recommendations for establishing beetle banks in areas of Oregon with precipitation greater than 40 inches per year (typically west side of the Cascades).

Common name / Species name / Seeding rate* (single species rate) / Seeding rate (1 of 3 species in a mix)** / Plug planting density*** / Notes
Blue wild rye / Elymusglaucus / 5.5 to 11 oz / 1000 ft2 / 1.8 to 3.7 oz / 1000 ft2 / 1/ ft2 / Grows to 6’ tall. Establishes quickly. Shade tolerant.
Slender Wild Rye/
Slender Wheatgrass / Elymus
trachycaulus / 5.5 to 11 oz / 1000 ft2 / 1.8 to 3.7 oz / 1000 ft2 / 1/ ft2 / Needs full sun.
California Oatgrass / Danthoniacalifornica / 3.7 to 6 oz / 1000 ft2 / 1.25 to 2 oz / 1000 ft2 / 1/ft2 / Tolerates wet and dry soils and shade. Slow-growing, but very long lived.
Roemer's Fescue / Festucaroemerii / 1.5 to 3 oz / 1000 ft2 / 0.5 to 1 oz / 1000 ft2 / 1/ft2 / For very well drained soils, such as sandy loams. Tolerates some shade.

Table 2. Native cool season grass recommendations for establishing beetle banks in areas of Oregon with precipitation less than 40 inches per year (typically east side of the Cascades).

Common name / Species name / Seeding rate* (single species rate, lbs/ac) / Seeding rate (1 of 3 species in a mix)** / Plug planting density** / Notes
Basin Wild Rye / Elymuscinereus / 5 to 10 oz / 1000 ft2 / 1.7 to 3.3 oz / 1000 ft2 / 0.3/ft2 / Large grass for areas with more than 14-inch precip. Commonly used in beetle banks.
Prairie Junegrass / Koeleriamacrantha / 0.75 to 1.5 oz / 1000 ft2 / 0.25 to 0.5 oz / 1000 ft2 / 1/ft2 / Best as a 3rd species in a mix in areas with more than 14 inch precip.
Big bluegrass / PoaSecundasspjuncifolia / 1.5 to 3 oz / 1000 ft2 / 0.5 to 1oz / 1000 ft2 / 1/ft2 / Good drought tolerant grass.
Bluebunch Wheatgrass / Pseudoroegneriaspicata ssp. spicata / 5 to 10 oz / 1000 ft2 / 1.7 to 3.3 oz / 1000 ft2 / 1/ft2 / Good for most situations and commonly used in beetle banks.
Snake River Wheatgrass / Elymuswawawaiensis / 5 to 10 oz / 1000 ft2 / 1.7 to 3.3 oz / 1000 ft2 / 1/ft2 / Best for less than 14-inch precipitation situations.
Idaho Fescue / Festucaidahoensis / 3 to 6 oz / 1000 ft2 / 1 to 2 oz / 1000 ft2 / 1/ft2 / For areas with more than 14 inch precip. Commonly used in beetle banks.

* If you have completed a full year of weed abatement, including eliminating cool and warm season weeds, and weed pressure is very low, sow seed at the lower seeding rate. If weed pressure is expected to be higher, then sow seed at the higher seeding rate.

** These rates are one third of the full rate and should be used in a mix of three grass species.

*** You may want to plant at higher rate to compensate for expected mortality. Plugs

Figure 2 (left to right): Predaceous ground beetle (genus Agonum) photo by Jesse Christopherson); Predaceous ground beetle (Pterostichusalgidus) photo by Charlene Wood;Wolf spider by Ian Marsman. All photos courtesy of photographers via flckr creative commons.

ESTABLISHMENT AND MAINTENANCE

New beetle banks will often require mowing or string-trimming at 8 inches or higher during the first year after planting to suppress annual weeds that may shade and compete with the newly established bunch grasses. Ongoing management in future years will require control of woody plants and spot-spraying, burning, or pulling weeds. Over time, as the grasses mature, weed encroachment should be reduced. To help with reseeding banks, mowing at 8 inches high after the bunch grasses have dropped seed will allow sunlight to reach the understory to help new seeds to germinate.

CONSIDERATIONS

As with all beneficial insect habitat, it is important to protect beetle banks from insecticide spraying.

ACKNOWLEDGEMENTS

These specifications were developed by Mace Vaughan (Xerces Society for Invertebrate Conservation) and Chris Hamilton (Oregon NRCS), with input from Gwendolyn Ellen (Oregon State University, Integrated Plant Protection Center), Annie Young-Matthews and Amy Bartow (NRCS Corvallis Plant Materials Center), Kathy Pendergrass (Oregon NRCS), Richard Fleenor (Washington NRCS), and Eric Mader, Thelma Heidel-Baker and Jarrod Fowler (Xerces Society). Original text developed by the Xerces Society, in their publication Habitat Planning for Beneficial Insects: Guidelines for Conservation Biological Control (

RESOURCES

For more information about beetle banks, explore the following resources.

  • Xerces Society Conservation Biological Control resources
  • Oregon State University, Integrated Plant Protection Center Farmscaping for Beneficials project.

Client: / Date:
Location: / County/SWCD:
Contract #: / Tract/Field:
Planner:
Description
Beetle banks provide shelter for predatory ground beetles, spiders and other beneficial insects. The banks consist of long, elevated earthen berms planted with perennial bunchgrasses. They may occasionally be combined with native wildflowers, but dense stands of bunch grasses are critical. The grass crown structure provides overwintering cover for beneficial insects, especially beetles and spiders, which attack crop pests.Bare space between bunch grasses may also provide nesting sites for ground-nesting bees. Banks should be located adjacent to, or within, cultivated fields and are intended to promote rapid movement by beetles into crop fields when the growing season returns.
Management Objective(s) and Narrative Summary:Describe why the structure is needed, any risks identified, and details on how risks are being mitigated.
(Planner describe additional information on project. Is this part of an IPM plan? Describe any moderate or high risks to beneficial insects and provide detail on how the risk(s) are being mitigated or addressed.)
As with all beneficial insect habitat, it is important to protect beetle banks from insecticide spraying.
GeneralSpecifications
Beetle banks are often positioned in the center of crop fields and extend almost to the field edges, leaving enough room on each end for equipment turns. The size of crop fields may necessitate multiple beetle banks positioned at regular intervals to account for the dispersal distance of ground beetles and other beneficial insects.Current guidelines recommend at least one beetle bank per 50 acres.In order to maximize success, the mound formation and site preparation step benefits from a full growing season of weed abatement. In this case, mounding occurs in the fall of year 1, followed by multiple rounds of weed control on the mound in the spring and summer,prior toseeding or plugging grasses in the fall of year 2. If mounding occurs in spring, a higher seed rate is required to increase competition with cool season weeds. For organic operations, the site preparation will typically include hand-pulling, mowing, solarization, and/or flame-weeding after the berm is created. Note that minimizing ground disturbance after mounding is critical to prevent bringing additional weed seed to the surface, where it may germinate. For conventional farms, site preparation will typically include 3 applications of labeled broad-spectrum herbicide targeting cool and warm season weeds through the growing season. The exception would be where weed pressure is expected to be very low. In this case, the landowner also could consider mounding, planting plugs, and heavily mulching in the fall.
Specifications
Component / Example / Specification for this farm
Beetle bank dimensions (average) / 1.5’ high x 3’ wide x 250’ long
Number of beetle banks / Three (see plan map)
Total area / 6,750 sqft (3 x 2,250sqft)
Mound construction / Use moldboard plow to build mounds in Sep-Nov
Site preparation / Spray non-persistent labeled herbicide or flame-weed as banks green up (e.g. March, May, late-June). Do not allow weeds to go to flower!
Seeding date / Sept. 1 – Oct. 15
Seeding method and seed mix / Evenly broadcast and roll:
  • 12.2ozBlue wild rye (1.8 oz per 1,000 ft2)
  • 3.4oz Roemer’s fescue (0.5 oz per 1,000 ft2)
  • 12.2 oz California brome (1.8 oz per 1,000 ft2)

Seeding other / Rake lightly, then apply 80 lbs clean weed-free straw per 1,000 sq. ft.
Post-seeding weed control / Spray labeled broad-leaf herbicide or high mow if needed
Other / Optional: Irrigate if possible until rains start.
Additional specifications
Operation, Maintenance, and Monitoring:
Beetle banks are intended to be permanent structures that will provide permanent cover for beneficial insects within annually tilled lands. Weed encroachment should be minimal once the grasses mature and the bank is established, usually within 1 to 3 years. The banks will require intermittent maintenance into the future, including the control of woody plants and spot-spraying or pulling weeds.
As with all beneficial insect habitat, it is important to protect beetle banks from insecticide spraying or drift.
Practice Code
No. /
Practice
/
Lead
Discipline /
Controlling
Factor / Units / Job Class
I / II / III / IV / V
643 /
Restoration of Rare or Declining Natural Communities
/
BCSD-Bio
/ Area / ac / 10 / 40 / 160 / 400 / All
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The Client acknowledges that:

a.They have received a copy of the specification and understand the contents and requirements.

  1. It shall be the responsibility of the client to obtain all necessary permits and/or rights, and to comply with all ordinances and laws pertaining to the application of this practice.

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I have completed a review of the information provided by the client or have conducted a site visit and certify this practice has been applied according to NRCS standards and specifications.

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