Spraying Asparagus in Fern

Jason DeveauOMAFRA, Simcoe

@spray_ guy

To improve a spray job, applicators require a holistic understanding of the factors that affect a spray job.

To improve a spray job, applicators require a holistic understanding of the factors that affect a spray job.

And it turns out there are quite a few factors…

We don’t have enough time to discuss all these factors.

We don’t have enough time to discuss all these factors.

We’ll focus on droplet behavior.

We don’t have enough time to discuss all these factors.

We’ll focus on droplet behavior.

Then, we’ll put it into practice in an experiment we ran in asparagus.

A nozzle produces a range of droplet sizes from Finer to Coarser.

A nozzle produces a range of droplet sizes from Finer to Coarser.

DV 0.5(VMD)

The median droplet size (DV 0.5) changes with pressure (lower = coarser).

The Finer the spray quality, the more droplets.

The Finer the spray quality, the more droplets.

The Coarser the spray quality, the fewer droplets.

The Finer the spray quality, the more droplets.

The Coarser the spray quality, the fewer droplets.

More sounds better, but the spray has to get to the target before it can provide coverage…

Droplets slow as they get further from the nozzle.

Droplets slow as they get further from the nozzle.

1 cm away:All droplets: 70 km/h

Droplets slow as they get further from the nozzle.

1 cm away:All droplets: 70 km/h

50 cm away: Coarser Drops: 28 km/hFiner Drops: 7 km/h Dr. Tom Wolf, Agrimetrix

Droplets slow as they get further from the nozzle.

1 cm away:All droplets: 70 km/h

Droplet speed and size

affects how they move in a

canopy.

50 cm away: Coarser Drops: 28 km/hFiner Drops: 7 km/h Dr. Tom Wolf, Agrimetrix

Imagine dividing a crop canopy into top, middle and ground (bottom).

Look straight down from the nozzle – how deep can you see?

Look straight down from the nozzle – how deep can you see?

Targets in line-of-sight are most easily hit.

Actually, because the sprayer is moving, spray behaves more like this…

Sprayer Direction

The droplets in the spray fall at different rates, and behave differently.

Coarser move in straight lines.

Coarser move in straight lines.

They move down and with the direction of travel.

Finer move with wind, and are influenced by everything.

When a droplet reaches the target, droplet size affects how they interact with one another.

≤Fine dropletspenetrate and

cover moresurfaces, but

drift

≤150 µm

150-300 µm

Medium dropletsprovide good coverage withmoderate drift

≤Fine dropletspenetrate and

cover moresurfaces, but

drift

≤150 µm

150-300 µm

Medium dropletsprovide good coverage withmoderate drift

≤Fine dropletspenetrate and

cover moresurfaces, but

drift

≤150 µm

≥Coarse dropletsrun off, bounce or miss small targets. Poor penetration,

but low drift

≥300 µm

150-300 µm

Medium dropletsprovide good coverage withmoderate drift

≤Fine dropletspenetrate and

cover moresurfaces, but

drift

≤150 µm

≥Coarse dropletsrun off, bounce or miss small targets. Poor penetration,

but low drift

≥300 µm

Same as ≥Coarsebut may also shatter and

improve coverage

≥300 µm (AI)

So, we need the Goldilocks Droplet:

So, we need the Goldilocks Droplet:

Too big: Bounce/run off or miss target Too small: Evaporate or drift away

So, we need the Goldilocks Droplet:

Too big: Bounce/run off or miss target Too small: Evaporate or drift away“They have to be

juuuuuuustright”

Diseases such as purple spot can have major economic impacts.

Diseases such as purple spot can have major economic impacts.

The best line of defence is spraying the appropriate control products.

But we’re spraying through the perfect

filter…

But we’re spraying through the perfect

filter…

But we’re spraying through the perfect

filter…

Needle-shaped leaves are excellent at intercepting spray.

In 2012 we tested five popular nozzle types, at two ground speeds using three carrier volumes to answer these questions:

In 2012 we tested five popular nozzle types, at two ground speeds using three carrier volumes to answer these questions:

Q1 - Does spray volume impact spray coverage?

In 2012 we tested five popular nozzle types, at two ground speeds using three carrier volumes to answer these questions:

Q1 - Does spray volume impact spray coverage?

Q2 - Which nozzle style gives the best coverage?

In 2012 we tested five popular nozzle types, at two ground speeds using three carrier volumes to answer these questions:

Q1 - Does spray volume impact spray coverage?

Q2 - Which nozzle style gives the best coverage?

Q3 - Does travel speed impact spray coverage?

This was repeated three times and target coverage was determined both as droplet deposits per cm2 and total percent covered.

Easy to hit

Hard to hit

VERY Hard to hit

125 L/ha 85 L/ha 45 L/ha

Fine

Medium

Coarse

VeryCoarse

ExtremelyCoarse

Water-sensitive paper: Fast, easy and effective feedback.

Dr. Tom Wolf, Agrimetrix

125 L/ha 85 L/ha 45 L/ha

Fine

Medium

Coarse

VeryCoarse

ExtremelyCoarse

Water-sensitive paper: Fast, easy and effective feedback.

Dr. Tom Wolf, Agrimetrix

Appropriate

Coverage

Q1 – Does spray volume impact spray coverage?

• 187 L/ha (20 US g/ac)• 234 L/ha (25 US g/ac)• 280 L/ha (30 US g/ha)

Q1 – Does spray volume impact spray coverage?

• 187 L/ha (20 US g/ac)• 234 L/ha (25 US g/ac)• 280 L/ha (30 US g/ha)

Combined results from

5 different nozzles at 16 km/h (10 mph).

Q1 – Does spray volume impact spray coverage?

Results: All cards received a significantly higher average deposit per cm2 and significantly higher average percent coverage at higher spray volumes.

Q1 – Does spray volume impact spray coverage?

Q2 – Which nozzle style gives the best coverage?

• Hollow cone (F)• XR Flat fan (F)• Dual flat fan (M)• Guardian Air (C)• Air-induced hollow cone

(C)

Q2 – Which nozzle style gives the best coverage?

• Hollow cone (F)• XR Flat fan (F)• Dual flat fan (M)• Guardian Air (C)• Air-induced hollow cone

(C)

We used 280 L/ha (30 US g/ac) at 16 kph (10 mph).

Q2 – Which nozzle style gives the best coverage?

Results: Tough to interpret.If we ignore the top target (excessive coverage from all tips) then it’s the XR Flat Fan and the Hollow Cone in the lead.

Finer droplets penetrate better.

Q2 – Which nozzle style gives the best coverage?

Q3 – Does travel speed impact spray coverage?

• 8 k/hr (5 mph)• 16 k/hr (10 mph)

Q3 – Does travel speed impact spray coverage?

• 8 k/hr (5 mph)• 16 k/hr (10 mph)

Since the hollow cone and XR flat fan did best at 280 L/ha (30 US g/ac) we used those

variables.

Q3 – Does travel speed impact spray coverage?

Results: While variability was high, the trend suggested a higher speed improved canopy penetration.

Sprayer wake and low boom may have helped.

Q3 – Does travel speed impact spray coverage?

If you use Finer droplets at high travel speeds in large volumes you may have improved results.

If you use Finer droplets at high travel speeds in large volumes you may have improved results.

This is not a good message…

Hollow cones in gusting wind.The photo doesn’t do it justice…

It is irresponsible to use med-fine spray quality without some form of drift mitigation (e.g. shrouds, air-assist or even drift-mitigating adjuvants)

Air Assist in Soybean (2015)

This is the best of both worlds: Finer droplets AND reduced

drift!

• Be systematic when trying to improve spray coverage. One change at a time.

• Be systematic when trying to improve spray coverage. One change at a time.

• Take direction from water-sensitive paper (multiple locations).

• Be systematic when trying to improve spray coverage. One change at a time.

• Take direction from water-sensitive paper (multiple locations).

• Higher volume (and usually slower travel speed) improve coverage.

• Finer spray improves penetration / coverage, BUT so much drift.

• Finer spray improves penetration / coverage, BUT so much drift.

• Consider Medium spray quality with air assist.

• Finer spray improves penetration / coverage, BUT so much drift.

• Consider Medium spray quality with air assist.

• Be aware of the impact of weather and crop staging.

Tom Wolf@nozzle_guy

Jason Deveau@spray_guy

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