vegetative barriers to spray drift

Vegetative Barriers to Pesticide Drift

Dr. Jason S.T. DeveauApplication 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.


• When pesticide drift warrants legal action, it often has a monetary penalty and can destroy neighborly relations.


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 ZoneC – 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 ZoneC – 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.


• 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.


• 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.


• 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.


• 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.


• 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 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).

Some Take-home Points


• 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 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.


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

vegetative barriers to spray drift

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