Vegetative filter strips for runoff mitigation

On this page

• Overview of pesticide runoff
• Vegetative filter strips for runoff mitigation
• When you need a vegetative filter strip
• When you do not need a vegetative filter strip
• Vegetative filter strips vs. other buffers
• Constructing vegetative filter strips
• Maintaining vegetative filter strips
• Getting help
• Appendix A – Research that supports the 10 metre width of vegetative filter strips

Overview of pesticide runoff

Farmers and growers use pesticides on soil or plant surfaces to protect crops from pests like insects, weeds and fungal diseases. After you apply pesticides, they can land on the soil surface. During rain, irrigation, or when snow melts, water runs down slopes and hills. The water picks up bits of soil. Soil travelling in water is called sediment. This water is called runoff. Runoff water can also pick up pesticides as it flows downhill. Some pesticides dissolve in runoff water, and others attach to sediment in the runoff. Runoff then flows into nearby surface waters. Surface waters are bodies of water that are above ground, like streams, rivers and lakes. When runoff enters surface waters, it can harm the ecosystem. To help maintain healthy ecosystems, and support biodiversity and healthy food chains, the amount of pesticides in surface waters must be kept to a minimum.

Factors that increase pesticides in runoff include:

• runoff that happens soon after pesticide application
• precipitation or irrigation that lasts a long time or is intense
• frequent pesticide application
• soil that does not drain well (like compact or clay soils)
• sloped areas treated with pesticides (steep slopes have more runoff)
• large areas treated with pesticides
• the amount of pesticide used
• higher rates of treatment than listed on the label

Vegetative filter strips for runoff mitigation

There are different ways to lower or mitigate the amount of pesticide that enters surface waters. Mitigation helps protect life forms in water, including many species of plants, algae, invertebrates and fish. Vegetative filter strips are one type of mitigation measure. A vegetative filter strip is a permanent, plant-filled strip of land. It's constructed between the sloped edge of an application area and the water where that area drains. A treatment area or application area is a section of land where you use pesticides, like cropland, fields or orchards. The dense plants in a vegetative filter strip slow the runoff so soil and pesticides settle before they can flow into surface waters.

Additional benefits

In addition to protecting the health of land and water, vegetative filter strips can also:

• reduce other pollutants in runoff (like nutrients and heavy metals)
• reduce soil erosion
• improve soil quality
• increase the stability of slopes
• improve surface water and groundwater quality
• reduce flooding
• improve wildlife habitats
• improve the appearance of land

When you need a vegetative filter strip

You must have a vegetative filter strip when both the following conditions are met:

• your pesticide label lists it as a mandatory requirement
• you apply pesticides near a sensitive aquatic habitat

Pesticide labels

Every pesticide goes through a risk assessment to determine if it is harmful to organisms. If a pesticide poses a risk to organisms in water because of runoff, then a vegetative filter strip may be a mandatory requirement on the product label. You can find this information in the "Environmental precautions" and "Directions for use" sections of your product label. Pesticides that require a mandatory vegetative filter strip will include the label statement "To reduce risk to aquatic organisms from runoff, a vegetative filter strip of at least 10 metres wide between the application area edge and adjacent, downhill aquatic habitats must be observed".

Pesticides that require vegetative filter strips:

• are toxic to organisms in water
• attach easily to soil
• are persistent (don't breakdown quickly in the environment and can realistically end up in surface waters)

Labels on all outdoor commercial pesticides have recommendations to reduce runoff. This includes a vegetative filter strip. It is important to read the entire label carefully. In most cases, a vegetative filter strip is not required, but is recommended as a best practice.

Sensitive aquatic habitats

A vegetative filter strip may be required when a pesticide is applied near a sensitive aquatic habitat. A sensitive aquatic habitat is as permanent body of water (present throughout the year) that is at the bottom of a slope in an area treated with pesticide.

Sensitive aquatic habitats include, but aren't limited to:

• commercial fish farms
• estuaries
• reservoirs
• sloughs
• lakes
• ponds
• rivers
• streams, creeks and brooks
• wetlands (Class III and above, including marshes, prairie potholes, swamps and open wetlands)

Full Glossary of terms for environmental water monitoring for pesticides.

Ditches that have a source of water other than runoff from the application area (such as spring or groundwater-fed ditches) require a vegetative filter strip.

Slope

If your application area has any sloped ground (greater than 0% slope) that causes runoff to flow into an aquatic habitat, you must have a vegetative filter strip. This is true even if there are changes in slope within the pesticide application area.

When you do not need a vegetative filter strip

Vegetative filters strips are not always required, but are recommended as a best management practice. Even narrow strips will remove some of the pesticide in runoff.

Areas that do not require a vegetative filter strip include:

Temporary bodies of water

Temporary water bodies exist for only part of the year. For example, waters caused by flooding or drainage to low areas of the application area. These are not considered sensitive aquatic habitats and do not require a vegetative filter strip.

Ditches and basins

Agricultural drainage ditches, catch basins and roadside ditches remove excess water from application areas. These water bodies are normally highly managed. These areas do not have a source of water other than runoff. They are not part of the natural waterways that drain a watershed.

Flat and or upward sloping application areas

If none of your application area slopes down towards an aquatic habitat, or if it is truly flat, then a vegetative filter strip is not required.

If there is a section of your application area that slopes upward just before the aquatic habitat, and there is no possible way for runoff to flow into the habitat, then you do not need a vegetative filter strip. This type of upward slope around an application area is rare because it can increase waterlogging.

Vegetative filter strips vs. other buffers

Spray buffer zones

A vegetative filter strip and a spray buffer zone are not the same. A vegetative filter strip protects aquatic habitats at the bottom of a slope from pesticides carried in runoff. A spray buffer zone protects sensitive habitats that are downwind from pesticide spray drift. A spray buffer zone is temporary while a vegetative filter strip is permanent.

Where you need a spray buffer zone

A spray buffer zone is required downwind from where you apply pesticides to protect aquatic and terrestrial habitats from pesticide spray drift. If you use herbicides, make sure that they don't damage plants in the vegetative filter strip. In most cases, spray buffer zones aren't required to protect a vegetative filter strip. But, they can be useful to prevent damage to the strip.

Where you might need both a vegetative filter strip and a spray buffer zone

In most cases, a vegetative filter strip isn't considered a sensitive habitat and doesn't need to be protected with spray buffer zones. If your vegetative filter strip includes existing sensitive terrestrial habitat (for example, trees along a river bank), only that part of your vegetative filter strip will need to be protected from spray drift.

If the product you're using requires spray buffer zones, they will be listed on the label under "Directions for use". If an aquatic spray buffer zone is required, you may include the width of the vegetative filter strip in the measurement of the spray buffer zone. Figures A and B are examples of how vegetative filter strips and spray buffer zones may overlap. In these examples, the pesticide requires a 15 metre aquatic spray buffer zone and 10 metre vegetative filter strip. Only 5 metres of the crop will need to be left unsprayed as a spray buffer zone. Wind direction changes the location of your spray buffer zones but doesn't change where you build a vegetative filter strip.

Figure A and B - Text description

Figure A

The application area slopes down to the east (right). There are aquatic habitats on the east and west (left) sides of the application area. The wind is blowing to the west. The aquatic spray buffer zone is at the top of the slope and protects the aquatic habitat west of the application area when a pesticide is applied. A spray buffer zone isn't required to protect the aquatic habitat to the east of the application area because the wind is blowing to the west. Any pesticide drift is blown west. A 10 metre wide vegetative filter strip is required at the bottom of the slope next to the water to protect it from runoff. The water west of the application area doesn't need a vegetative filter strip because it isn't at the bottom of a slope.

Figure B

The application area slopes down to the east (right). There are aquatic habitats on the east and west (left) sides of the application area. The wind is blowing to the east. A 15 metre aquatic spray buffer zone is on the east side of the application area. The buffer zone protects the water east of the application area when the pesticide is applied. A 10 metre-wide vegetative filter strip is required at the bottom of the slope next to the water to protect it from runoff. The 10 metre vegetative filter strip is in the 15 metre aquatic spray buffer zone. The spray buffer zone is 5 metres wider than the vegetative filter strip. The water west of the application area doesn't need a vegetative filter strip because water isn't at the bottom of a slope.

Vegetative filter strips vs. riparian buffers

Riparian buffers are similar to vegetative filter strips but they are not the same thing. Riparian buffers are strips of vegetation along surface waters that help stop soil erosion. They are much larger than vegetated filter strips and contain more complex plant communities. Riparian buffers also increase and connect habitats for biodiversity. They usually have three stages of plants: grass by the application area edge, followed by a band of shrubs, and finally a band of trees up to the bank of the water. Both riparian buffers and vegetative filter strips are vegetated areas of land along surface waters. They are both effective at removing soil and pesticides from runoff waters.

Constructing vegetative filter strips

Choosing plants

The plants in a vegetative filter strip should consist of mostly dense grasses. Grasses trap sediment and pesticides better than shrubs or trees. Grasses are also less expensive and time-consuming to establish.

You should choose grasses that work with your local growing conditions. When you choose grasses for a vegetative filter strip, look for ones that:

• adapt to the location
• compete with surrounding plants
• have deep roots
• are perennial (grow back every year)
• are native to the area (if possible)
• form sod
• are sturdy
• grow tall

Vegetative filter strips may also include shrubs, trees and other perennials. Annual plants are not appropriate for a vegetative filter strip since they do not provide protection outside their growing period. Shrubs and trees can also benefit wildlife and add to the look of your property.

Table 1: Examples of grass species that can be effective in a vegetative filter strip (adapted from Haan et al. 1994 and Muñoz-Carpena & Parsons 2020).

Species	DensityFootnote 1 (stems/m2)	Grass spacing (cm)	Maximum height (cm)
Tall fescue	3900	1.63	28
Blue gamma	3750	1.65	25
Ryegrass (perennial)	3900	1.63	18
Weeping lovegrass	3750	1.65	30
Bermudagrass	5400	1.35	25
Bahiagrass	N/R	N/R	20
Centipedegrass	5400	1.35	15
Kentucky bluegrass	3750	1.65	20
Grass mixtureFootnote 2	2150	2.15	18
Buffalograss	4300	1.50	13
cm centimetres m metres N/R not reported Footnote 1 The given densities are for a good stand; to convert to poor, fair, very good, and excellent stands, multiply by 1/3, 2/3, 4/3, and 5/3, respectively. Return to footnote 1 referrer Footnote 2 Values depend on the exact mixture; if a given species predominates, values for that species should be used. Return to footnote 2 referrer

Existing vegetation

You don't need to remove existing shrubs and trees. That may have a negative impact on the habitat the vegetative filter strip is trying to protect. If you need to add grasses to the existing vegetation, then the grass should be planted on the side of the vegetative filter strip closest to/within the application area.

Choosing the construction area

If your application area has any sloped ground (greater than 0% slope) that has pesticide runoff flowing into an aquatic habitat, you must have a vegetative filter strip. The vegetative filter strip must be constructed between the application area and surface waters at the bottom of the application area.

Defining the edge of the water and flooding

The edge of an aquatic habitat is the typical high-water mark. The typical high-water mark is the highest point the water rises during a year without extreme weather events or flooding. When a vegetative filter strip floods, it is less efficient at trapping runoff and pesticides. Periodic, temporary flooding is inevitable. For example, in spring after snow melts. A vegetative filter strip should not be in an area where it will flood repeatedly throughout a typical growing season.

Construction requirements

The vegetative filter strip should slope gently down towards the water. It should be as uniform and even in width as possible along the bank of the water. You should prepare the soil for seeding by roughening it with disking, harrowing or raking. You may need to amend the soil to improve growing conditions for your grasses or plants. You may also need to put down mulch to protect seedlings.

Height

There is no set rule for how tall the grasses in a vegetative filter strip must be. The vegetation should be tall enough that large amounts of runoff don't flow over the plants. But, vegetation should not be so tall that it's flattened by runoff. The grass in a vegetative filter strip should be mowed to a minimum height of ~ 15 centimetres (6 inches). But, this depends on the species of grasses that you plant. If you mow grass shorter than 15 centimetres, the vegetative filter strip may not slow the runoff enough to be effective.

Width

Vegetative filter strips should:

• be at least 10 metres (30 feet) wide from the typical high-water mark to the edge of the application area (Figure 3)
• Learn more about research that supports the 10 m width.
• be along the entire edge of surface waters that are in the pesticide application area

Figure C - Text description

The pesticide application area is at the top. The surface water is at the bottom. Arrows point down along the application area to represent the direction of runoff. A vegetative filter strip is between the pesticide application area and the surface water. The edge of the water is not a straight horizontal line from left to right. The vegetative filter strip is 10 metres in width along the entire edge of the water.

Troubleshooting

Growing in extreme weather

You should choose grass species that grow well in your local climate. For example, hot, dry areas should have drought-resistant grasses. You might need gentle irrigation to establish and maintain your plants. If you need to irrigate your vegetative filter strip, then do it well before or well after pesticide application.

Concentrated flow and channeling

Concentrated flow and channeling happen when runoff from different areas of a application area come together. This creates large amounts of fast flowing water that can wear paths through plants and soil. The speed and amount of water means the strip is less effective at filtering soil and pesticides. Runoff must enter the vegetative filter strip evenly along the edge of the application area. You may minimize water flow using:

• berms – a ridge that breaks the angle of a slope
• terraces – constructed embankments across a slope that divert or store surface runoff
• conservation tillage – reducing the number of tilling passes and leaving crop residue like roots and stems
• seed sowing – sow seeds perpendicular to the water

Maintaining vegetative filter strips

You need to maintain your vegetative filter strips so they are effective. Maintenance should include the following:

• Look for bare spots and signs of erosion (such as rills or gullies), especially after periods of intense runoff. For example, during and shortly after heavy rainfall, irrigation or snowmelt.
• Repair and reseed any bare spots or areas with signs of erosion.
• Remove built-up soil piles in the vegetative filter strip at the end of the growing season. Soil piles can be shoveled manually or with machinery. This soil can be spread back on your application area or growing areas. Any areas damaged by removing soil should be repaired and reseeded.
• Depending on the type of grass, mow occasionally to maintain a height of about 15 centimetres (6 inches). Grass should not be so long that it falls over or so short that runoff flows over it.
• Limit disturbances like machinery and livestock traffic in the vegetative filter strip. Frequent disturbances can compact and damage the soil so it erodes easier.
• Irrigate plants occasionally as needed to maintain growth.
• Condition or amend the soil as needed.

Getting help

Vegetative filter strips are a recommended best management practice for farmers. Provincial extension officers can give you resources to help with runoff mitigation.

If you need more information about vegetative filter strips, please contact the Pest Management Information Service.

Appendix A – Research that supports the 10 metre width of vegetative filter strips

Health Canada did a detailed analysis of scientific literature. Studies support that a 10 metre vegetative filter strip mitigates risks from pesticide runoff for aquatic organisms. This 10 metre width is a requirement across Canada. Here is a summary of the key studies:

Robinson et al. (1996) studied 13 different periods of rain that had varying intensities, from light to very heavy rain. During heavy rain, more pesticides are expected to flow into water bodies. The study defined heavy rain as rainfall between 18 millimetres to 72 millimetres, with no specific time limit. The results showed that on a 7% slope, vegetative filter strips that were 3 metres, 6 metres, and 9 metres wide could hold back around 50%, 75%, and more than 95% of soil carried by the runoff, respectively. If we assume that both soil and pesticides are lost in the same amount, then using 3 metres and 6 metres wide vegetative filter strips could reduce 50% and 75% of pesticides in runoff that reach surface waters. Even with a 50% to 75% reduction, the pesticides in runoff water could still be above what's safe for aquatic organisms. A 9 metres wide vegetative filter strip could reduce more than 95% of pesticides. Runoff from a 9 metres strip is less likely to be unsafe for aquatic organisms. It's important to note that real-world conditions in Canada (like different rainfall intensity and duration, soil types and steeper slopes) could lead to less soil being held back.

Abu-Zreig et al. (2004) did a study in Guelph, Ontario. They looked at different widths of vegetative filter strips (2 metres, 5 metres, 10 metres, and 15 metres) and different slopes of land (2.3% and 5.0%). The researchers found that the width of the vegetative filter strip was the most important factor in how much soil was deposited by runoff water. Syversen (2005) did a study in southern Norway. They looked at vegetative filter strips that were 5 metres and 10 metres wide to check how much soil was deposited from runoff. The results showed that the 10 metre strip held more soil compared to the 5 metre strip. Both studies agreed that a 10-metre-wide vegetative filter strip is better at trapping soil than a narrower strip.

In Prince Edward Island, researchers Dunn et al. (2011) ran a study to check how well vegetative filter strips could remove seven commonly used pesticides. They tested vegetated filters strips in widths ranging from 10 metres to 30 metres. A 10 metre vegetative filter strip was highly effective at removing pesticides that strongly attach to soil. Vegetative filter strips must be wide enough to slow down the water so pesticides that are bound to soil particles drop out of the flowing water.

Based on the current evidence, Health Canada determined that a 10 metre vegetative filter strip is necessary to lower the levels of pesticides in runoff. This helps decrease the risk to aquatic organisms. Constructing and maintaining vegetative filter strips helps reduce runoff from pesticides that share similar characteristics to pesticides in the studies (like easily attaching to soil, not easily dissolvable, long-lasting and harmful to aquatic organisms). Work is underway to determine if we can refine vegetative filter strip widths for specific locations and pesticides.

References

• Abu-Zreig, M., R.P. Rudra, M.N. Lalonde, H.R. Whiteley, and N.K. Kaushik. 2004. Experimental investigation of runoff reduction and sediment removal by vegetated filter strips. Hydrological Processes, 18: 2029-2037.
• Dunn, A.M., G. Julien, W.R. Ernst, A. Cook, K.G. Doe, and P.M. Jackman. 2011. Evaluation of buffer zone effectiveness in mitigating risks associated with agricultural runoff in Prince Edward Island. Science of the Total Environment, 409: 868-882.
• Haan, C.T., B.J. Barfield, and J.C. Hayes. 1994. Design hydrology and sedimentology for small catchments. Academic Press, San Diego.
• Muñoz-Carpena, R. and J.E. Parsons. 2020. VFSMOD-W Vegetative Filter Strip Modelling System: Model documentation & user manual. Version 6. University of Florida.
• Robinson, C.A., M. Ghaffarzadeh, and R.M. Cruse. 1996. Vegetative filter strip effects on sediment concentration in cropland runoff. Journal of Soil and Water Conservation, 51: 227-230.
• Syversen, N. 2005. Effect and design of buffer zones in the Nordic climate: the influence of width, amount of surface runoff, seasonal variation and vegetation type on retention efficiency for nutrient and particle runoff. Ecological Engineering, 24: 483-490.