Vegetative Barriers to Pesticide Drift Dr. Jason S.T. Deveau Application Technology Specialist February, 2012
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Vegetative Barriers to Pesticide Drift
Dr. Jason S.T. Deveau Application Technology Specialist
February, 2012
About Me
• Too many years in university as a student of plant cell physiology
• Five years as a consultant for companies that designed colleges and universities
• OMAFRA’s Application Tech Specialist (aka Spray Guy) since
2008 A Common Horticultural Pest – Spray on Sight
How Pesticide Drifts
• Before we can discuss how vegetative barriers can mitigate pesticide drift, we have to understand a little more about what drift is and how it happens.
• Luckily, OMAFRA and Croplife Canada just completed two videos explaining all about it.
• We’ll watch the first one in a minute…
• Pesticide drift can have adverse affects on wildlife and bystanders.
• Riparian Zones
• Open Water
• Tree Lines
• Rivers and Streams
• Recreational Areas
• Home Gardens
• Public Areas
• Residences
What can Pesticide Drift do?
• Pesticide drift can damage nearby crops, like this newly planted tomato field damaged by glyphosate from soybean. For multiyear crops, like grapes, the damage can last for years.
What can Pesticide Drift do?
• When pesticide drift warrants legal action, it often has a monetary penalty and can destroy neighborly relations.
What can Pesticide Drift do?
Let’s Watch “What is Pesticide Drift”
www.ontario.ca/spraydrift
How Wind Behaves
• Wind is slowed near the ground due to boundary-
layers that cause drag because of friction.
• Wind distorts and slows as it passes through porous barriers, then mixes and returns to
normal a little further on.
A – Wind Flow D – “Dead” Area in lee of tree
B – Displaced Flow E – Mixing Zone
C – Filtered Flow F – Re-Equilibrated Flow
How Wind Behaves
• Wind is deflected and speeds up over non-porous
barriers, and returns to normal much further on.
A – Wind Flow D – “Dead” Area in lee of tree
B – Displaced Flow E – Mixing Zone
C – Filtered Flow
How Wind Behaves
How Vegetative Barriers Affect Pesticide Drift
• Here is a narrow row vegetative barrier with about 50% optical porosity (you can see through
it easily).
• Narrow row vegetative barriers should be as close to the point of pesticide release as possible in order to intercept the spray.
• Studies have shown the height of the barrier should be a minimum of 2x the release height of
the pesticide.
How Vegetative Barriers Affect Pesticide Drift
• Spray-laden air passes through and over the barrier.
• The pesticide concentration doesn’t change above the barrier, but is filtered as it passes through.
• In the re-equilibrated zone, (a distance of 3-10 x the height of the barrier) pesticide-laden air
returns, but at a lower concentration.
How Vegetative Barriers Affect Pesticide Drift
• The lee of the barrier is well protected. This scrubbed layer provides LOCAL PROTECTION.
• A good use for narrow row vegetative barriers would be downwind of an agricultural operation,
adjacent to a stream.
How Vegetative Barriers Affect Pesticide Drift
• Here is a wide row vegetative barrier comprised of shrubs, grass, riparian plants, etc.
• Unlike a narrow row, it relies on natural surfaces to catch pesticide droplets as they pass through
over a longer distance.
How Vegetative Barriers Affect Pesticide Drift
• Some laden air passes through, and some over.
• The concentration of pesticide doesn’t change above the barrier, but is filtered out as it passes through.
• The re-equilibrated zone is much further away and pesticide-laden air returns at a much lower concentration due to dilution over a long distance.
How Vegetative Barriers Affect Pesticide Drift
• The downwind area well beyond the barrier received considerably less pesticide. This provides REGIONAL PROTECTION.
• A good use would be downwind of any agricultural area where there is room for the
strip.
How Vegetative Barriers Affect Pesticide Drift
How Artificial Barriers Affect Pesticide Drift
• In 2008, the University of Guelph published a study on the effect of windbreaks and buffer zones on spray drift deposition.
• They used combinations of 10 metre wide vegetative buffer strips and an “artificial”
windbreak made of snow fence.
• The fence was either 50% optical porosity, or when two layers were used perpendicular to each other (like a checker
board) it was 25%.
How Artificial Barriers Affect Pesticide Drift
• They found that the wide vegetative buffer strip alone provided sufficient drift protection from a field sprayer for up to 100 metres downwind from the buffer at winds of ~14 kph.
• Under wind conditions >14 kph, adequate protection was afforded by the same 10 metre wide vegetative buffer strip plus the dense (25% optical porosity) artificial windbreak.
• Alternately, the same protection was provided under wind conditions > 14 kph when a 10 metre wide vegetative buffer strip was used following a
20 metre wide buffer (aka no spray) zone.
• Thin, rough foliage should extend from base to crown (Miscanthus grass does very well: Van de Zande, ‘00).
• Trees with small and/or hairy leaves maximize droplet interception (needles beat leaves: Makarov et al., ‘96.).
• Row barriers should have about 50% optical porosity.
• Mixed plantings, or multiple bands of highly porous trees, ensure there are no gaps in the lower canopy.
• Barrier height should be 2x the pesticide release height , minimally.
• Barrier should be as close as practicable to the spray zone.
• A combination of wide followed by narrow row vegetative barrier would likely be best.
• A windbreak is not necessarily a vegetative barrier to pesticide drift, depending on what needs to be protected and where it is in relation to the barrier.
Some Take-home Points
Thank You
“Spray Drift Management – Principles, Strategies and Supporting Information – 2002” -PISC Report 82, Australia
‘
“Buffer Zone & Windbreak Effects on Spray Drift Deposition in a Simulated Wetland – 2004” -Brown, Carter and Stephenson, Pest Manag Sci 60:1085-1090
“Mathematical Models for Dispersal of Aerosol Droplets in an Agricultural Setting – 2008” -Harper, PhD Thesis, Massey U, Albany, New Zealand
“Drift Filtration by Natural and Artificial Collectors: A Literature Review” -Hewitt, 2001
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