Field Practice BMPs
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Sanitation
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Knock off "mummy fruit" to reduce pest problems in future years. Clean up or disk "mummies" to prevent future infestations.
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Orchard Floor Vegetation During Dormant Season
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Seeded or resident vegetation growing on orchard floors that is later mowed or disked.
Resident Vegetation - existing, unplanted mixture of annual or perennial weeds, crop species and/or native grasses and forbs which has adapted to management methods used in the orchard.
Seeded vegetation - cover crops that include many types of cultivated species including legumes (bell beans, peas, clover, medics and vetches) and grasses such as cereal grains, turf grasses and sudan grass.
Benefits
Orchard floor vegetation can reduce dormant spray pesticide runoff to surface waters in several ways:
- Can be easily encouraged to grow in the fall or early winter by a post harvest irrigation or early rains and requires little to no management to establish.
- Reduction in runoff volume through increased water infiltration.
- Reduction in sheet erosion caused by rainfall impact on bare ground.
- Decrease in pesticide mass carried by sediment.
- Shorter pesticide persistence (faster breakdown) on vegetation than soil.
- Adsorption of pesticides to plant surfaces.
- Anchors soil during winter rains preventing soil, nutrient and pesticide runoff.
- Allows pesticides to break down and be filtered onsite.
Adds organic material to the soil.
Accelerates the biodegradation of pesticides in soil.
Can reduce plant parasitic nematodes by antagonism.
Legume cover crops fix atmospheric nitrogen and release it to the orchard crop during the growing season.
Improves water infiltration, soil aeration and soil texture.
Improves soil fertility.
Assists in weed control (seeded covers).
Improves orchard access during wet weather.
Cover crops provide nectar sources, pollen and prey for beneficial predators.
Drawbacks
Difficult to manage if noxious weeds are present and requires mechanical or herbicide control in late winter or early spring if overgrown.
Increased cover and feed for gophers, ground squirrels and mice (also higher populations from increased habitat and reduced predation).
Increased humidity can potentially create conditions for fungal diseases.
Potentially increased nematode populations with summer-grown cover crop.
Higher water use with perennial cover crops.
Sprinklers can be blocked by climbing vetches.
Blooming cover crops can compete with tree crops for pollinator insects if not mowed.
Increased danger of frost damage. A tall, dense cover crop can reduce nighttime temperatures by up to 5 or 6 degrees, increasing the potential for frost damage. However, orchards with closely mowed cover crops and moist soil may be only about 1 degree colder than bare soil. Alternate row cover cropping can reduce the difference even more. Mowing before frost reduces the risk of frost damage.
Trash (plant residue, particularly grasses) at harvest can hinder almond pick-up. However, growing an annual legume cover crop mix that can be mowed and allowed to decompose over summer causes fewer harvest problems.
In almonds, perennials may interfere with harvest. Perennials are most suited for stone fruit orchards.
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Cover Crop Management
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Cover and Green Manure Crop
Plants are disked to incorporate organic material and improve soil fertility and tilth. Disking (or mowing) is generally done when plants are in full-bloom to post-bloom stage, depending on frost potential and soil moisture conditions.
Mowed Cover Crop
Managed by mowing to maintain at least 60% ground cover where erosion is possible. Mowing to 3-4 inches prior to frost can reduce cold temperature damage potential. Mowing intervals can often allow adequate seed production for following season re-growth. Mowed cover crops reduce dust during harvest operations and improve water infiltration rates.
Disked Cover Crop
Plants typically disked at full-bloom to post-bloom stage, depending on condition of the target crop, weather and soil moisture conditions. Maintain at least 60% ground cover where erosion is possible. Mowing to 3-4 inches prior to frost can reduce potential for cold temperature damage.
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Vegetative Buffers
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Areas or strips of land surrounding an orchard that are maintained in permanent vegetation.
To effectively trap pesticides, buffers must slow water runoff and increase infiltration so that pesticides can be trapped and degraded in buffer soil and vegetation.
Vegetative buffers are a tool to further improve water quality and provide additional benefits such as wildlife habitat and stream bank protection.
For best success, they should be used in conjunction with other mitigation practices.
Benefits
Can be used to manage soil, water, nutrients and pesticides while minimizing environmental impacts.
Effective in trapping eroded sediment, reducing runoff of pesticides that are adsorbed to soil particles.
Note: some pesticides (e.g. OPs) are highly water soluble and don't adsorb to soil particles as readily as others (e.g. pyrethroids).
Drawbacks
California-based research is limited on the potential for orchard filter strips and grassed waterways to reduce OP pesticide loading, although the practices have been shown to be effective in other regions of the U.S.
Uncertainties of buffers include: appropriate dimensions for volume of water flow; appropriate plant species and plant density for the soil types and rainfall zones; considerations for various locations; slope and channel dimensions for grassed waterways; and dimensions for constructed wetlands.
Can require growers to set aside productive acreage.
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Vegetative Filter Strips
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Areas of grass or other permanent vegetation used to reduce sediment, organics, nutrients, pesticides and other contaminants in runoff to maintain or improve water quality.
Vegetative filter strips are located between crop fields and water bodies, i.e. grassed roadways.
Plant material captures rainfall and retains nutrients. Roadways can be grassed or sod planted, as can sprayer mixing pads and wellheads.
Depending upon the site, a full border around an orchard may not be necessary for mitigating impacts to surface water.
Filter strips could be planted at low ends of fields or in other critical zones.
Benefits
Slows runoff allowing sediment to drop out of suspension.
Traps sediment with adsorbed pesticide residues.
Increases water infiltration into the soil profile.
Catches some pesticide drift, preventing it from reaching the soil.
Drawbacks
If water runoff is channeled, a grass strip may not effectively trap the adsorbed pesticides.
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Vegetative Barriers
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Narrow, permanent strips of stiff stemmed, erect, dense, perennial vegetation established in parallel rows and perpendicular to the dominant slope of the field.
Benefits
Effective in dispersing concentrated flow, thus increasing sediment trapping and water infiltration.
Drawbacks
If water runoff is channeled, a vegetative barrier may not effectively trap the adsorbed pesticides.
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Grassed Waterways
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Benefits
Helps slow the flow of water to a non-erosive level.
Provides a means of trapping sediment, nutrients, and pesticides while preventing gully erosion.
Provides habitat and cover for wildlife.
Drawbacks
Overgrown channels causing waterway breaching and flooding can restrict storm flows.
Due to the concentrated flow that normally occurs in waterways, sediment trapping and water infiltration can be minimal with large runoff events, but substantial with smaller events.
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Riparian Buffers
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Trees and shrubs planted adjacent to streams, lakes, ponds and wetlands.
Forest buffers are frequently combined with an understory of perennial grass buffers.
Benefits
Helps lower water temperatures by shading the water body.
Protects stream banks and slows out-of-bank flood flows.
Deep tree roots may intercept nitrate entering streams in shallow subsurface flow and provide soil carbon for microbial energy. Microbes can denitrify nitrate and degrade pesticides.
Woody vegetation provides food and cover for wildlife.
Contributes energy sources to aquatic communities.
Drawbacks
If water runoff is channeled, riparian buffers may not effectively trap pesticides.
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Constructed Wetlands
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Wetlands constructed at tile outlets or as part of riparian buffer systems for degrading pesticides and denitrifying nitrates.
Benefits
Provides confined area for breakdown of pesticides in water.
Drawbacks
Land needed for constructed wetlands is not readily available in high production areas. Available land can be costly.
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Hedgerows
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Fences of shrubs or trees in, across, or around a field.
Hedgerows can include an understory composed of perennial native grasses and forbs, a shrub midstory composed of California native species and occasionally a discontinuous overstory of valley and foothill trees.
Benefits
May reduce erosion by having perennial vegetation on a portion of the field.
If runoff flows across the hedgerow in sheet flow, sediment can be trapped, reducing the amount of sediment and sediment-borne pesticides from entering surface waters.
Can attract beneficial insects and provide competition against invasive weeds.
Windbreaks and hedgerows can provide drift mitigation, potentially reducing off-site movement of pesticides.
Because many of the native species used in hedgerows have deep roots that hold the soil and increase water permeability, there may be a reduction in water runoff and off site movement of sediment. This could reduce runoff of pesticides in the dissolved and sediment-borne phases of field runoff. However, no studies have quantitatively measured the reductions in OP pesticide runoff.
Drawbacks
Certain plant species may attract pests that can attack the crop or neighboring crops. Careful consideration must be given to the species of vegetation selected and the types of insects that may be attracted.
Plant species can provide habitat and attract endangered species. Safe Harbor Agreements are available to protect growers where a practice is implemented that could attract endangered species to their farms, a factor that should be evaluated and addressed before establishing hedgerows.
Some species can grow 10-15 feet wide, so space must be allowed for equipment to pass.
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Reducing or Eliminating the Herbicide-Sprayed Berm
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Berm areas of orchards sprayed with herbicides represent a bare conduit for runoff of rainfall or irrigation water.
By allowing vegetation to grow and reducing the berm width or seasonal spraying of the berm, runoff potential from an orchard could be reduced.
Options:
- Reduce strip spray widths by 25%.
- Apply herbicide in January/February after sprouted grass covers the berm.
- Spray a 5-foot square block around trees to keep the trunk area clean but leave vegetation on the remainder of the row berm.
- Stop spraying herbicides at the next-to-the-last tree in each row, leaving a vegetative barrier surrounding the orchard.
- Eliminate use of pre-emergence herbicides.
Benefits
Cost savings.
Reduction in runoff volume through increased soil infiltration.
Decrease in soil erosion and movement of pesticides with soil borne runoff.
Shorter pesticide persistence on vegetation than soil and better absorption on plant surfaces (faster degradation on plant matter). An orchard floor that is completely vegetated versus 25% bare soil has greater area for these mechanisms to function.
Drawbacks
Vegetation on berms can be difficult to manage in almond orchards.
Vegetation control can be difficult if excessive growth occurs before herbicide is applied.
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