Ginseng Sprayer Workshop – Lessons Learned

By: Dr. Jason S.T. Deveau, Application Technology Specialist, OMAF and MRA

If you missed the ginseng spray workshop this June, you missed out on some valuable information. Ginseng is notoriously difficult to spray: it is highly susceptible to pathogens given the high humidity and still conditions generally found under the shade structure. Further, it forms a solid ceiling of leaves that resist spray penetrating to the stem and crown below, and makes under-leaf coverage very difficult to achieve.

July 3 ARAG 1

Figure 1 – ARAG Microjet® nozzles

Many growers have (wisely) walked away from the Casotti® sprayers, which have been shown to give erratic coverage at best, and they have adopted the ARAG Microjet® system (see Figure 1). The ~$80.00 price tag for each nozzle is because of the brass mixing valve and swivel joint, as well as the fact that it is imported from Italy. Contrary to popular belief, it does not use air-assist, or air-induction – it is strictly hydraulic, with the possible exception of creating a ‘wake’ at high pressures which can create a little air movement. This phenomenon is called air inclusion, and it can be emulated by any droplet that is large enough and is travelling fast enough.

This nozzle is essentailly the business-end of a spray gun, and the way it is used in ginseng it works more-or-less like a hollow cone disc-core assembly. This raises the question of why not use the cheaper and more readily available ceramic disc-core? We set out to compare the two nozzles using water sensitive paper set within the canopy (see figure 2). These yellow, paper targets turn blue when sprayed, clearly showing spray coverage.

The first step was to determine the output rate for each nozzle. Generally, nozzle manufacturers provide rate tables showing how much volume a nozzle emits (e.g. US gallons per minute) at a given pressure. Finding these tables for the 1.5 millimetre ARAG Microjet® proved dfficult, and when one was finally obtained, it was discovered the rates were established for 200 to 850 pounds per square inch. This is excessively high pressure for a typical boom sprayer, so tables had to be developed for lower pressures. Further, given the odd design of the mixing valve, it was determined that moving the handle 10 degrees left of centre, or 10 degrees right of centre, gave a difference of as much as 60%. Table 1 shows the outputs for a 1.5 millimetre nozzle with the handle in both positions and Figures 3 and 4 express the rates graphically. Outputs were determined using the Innoquest Spot-On® SC-4, but the frothing effect created by the nozzles may have created minor errors. Each rate is the average of a minimum of three samples.

 July 3 water sensitive paper locations

Figure 2 – Location of water-sensitive papers in canopy

Table 1 – Average 1.5 mm ARAG Microjet® output at a range of pressures and three valve settings in US imperial and metric units

Valve Setting

Pressure (psi)

Avg Output (gpm)

Pressure (bar)

Avg Output (L/min)

10 degrees left

40

1.02

2.76

3.86

10 degrees left

50

1.1

3.45

4.16

10 degrees left

60

1.25

4.14

4.73

10 degrees left

70

1.25

4.83

4.73

10 degrees left

80

1.38

5.52

5.22

10 degrees left

90

1.4

6.21

5.3

10 degrees left

100

1.45

6.89

5.49

10 degrees left

110

1.6

7.58

6.06

10 degrees left

120

1.75

8.27

6.62

10 degrees left

150

1.87

10.34

7.08

10 degrees left

200

2.2

13.79

8.33

10 degrees right

40

0.65

2.76

2.46

10 degrees right

50

0.7

3.45

2.65

10 degrees right

60

0.8

4.14

3.03

10 degrees right

70

0.85

4.83

3.22

10 degrees right

80

0.9

5.52

3.41

10 degrees right

90

0.9

6.21

3.41

10 degrees right

100

1

6.89

3.79

10 degrees right

110

1.07

7.58

4.05

10 degrees right

120

1.1

8.27

4.16

10 degrees right

150

1.25

10.34

4.73

10 degrees right

200

1.37

13.79

5.19

July 3 Figure 3

Figure 3 – Average 1.5 mm ARAG Microjet® output at a range of pressures and two valve settings in US Imperial units

July 3 Figure 4

Figure 4 – Average 1.5 mm ARAG Microjet® output at a range of pressures and two valve settings in Metric units

Using the grower’s typical ground speed of 5 km/hr (~3 mph) and operating pressure of 6.9 bar (100 psi), we found four TeeJet® disc-core combinations that emitted a hollow cone pattern and approximately the same output as the ARAG Microjets®. The five nozzles sets tested were:

1)      ARAG Microjet 1.5 mm = ~0.95 US g/min avg at 100 psi

2)      D8-DC25=      0.97 US g/min at 100 psi=      ~97° cone

3)      D7-DC45=      0.97 US g/min at 100 psi=      ~81° cone

4)      D4-DC46=      0.88 US g/min at 100 psi=      ~33° cone

5)      D6-DC45=      0.93 US g/min at 100 psi=      ~81° cone

We did not use nozzle drop hoses (aka drop arms or hose drops) because it has been firmly established that they are absolutely required to achieve under leaf coverage (see OMAF and MRA factsheet 10-079 at http://www.omafra.gov.on.ca/english/crops/facts/10-079.htm ).

While there were some complications with setting up the papers for the demo, we observed the following:

1)      The output of each Microjet® nozzle can be as much as 50% more or less than expected without being visually detectable and output for each nozzle must be confirmed before spraying. Therefore, outputs should be confirmed before every application.

2)      Microjets® at 100 psi emitting ~890 litres per hectare (~95 US gallons per acre) gave satisfactory coverage on all upward facing targets, but unsatisfactory under-leaf coverage. This has been demonstrated many times before.

3)      The D7-DC45 combination emitting a similar rate gave satisfactory coverage on all upward facing targets, but unsatisfactory under-leaf coverage. They may be a viable alternative to the Microjets®.

4)      Nozzle drops are advised to achieve under-leaf coverage.

The demo also raised some questions:

1)      Did the disc-core push the canopy apart as much as the Microjet®? The audience noticed there was some leaf-shadowing where the cards did not get complete coverage using disc-core. This might have been coincidence, or it may not have. This question will be addressed in a research trial next season, but for now, the D7-DC45 appeared to give similar coverage to the Microjet®.

2)      Can nozzle drops be avoided if pressure is raised to 27.5 bar (400 psi)? Thanks to one grower trying this experiment in his garden after the demo, we saw some underleaf coverage is possible at such high pressures, but this occurred at the cost of a lot of noise, diesel fuel and considerable wear on the ceramic Microjet® discs. The grower tested these tips and discovered they needed replacement after only two years of use. Nozzle drops are cheaper, easier and result in considerably more spray in the under leaf positions.

3)      We saw what minimal and excessive foliar coverage looked like, and determined how much variability there was from one nozzle to another. A significant question was “How much spray can be saved when using a more accurate application?” and the answer is yet to be determined, but could be well in excess of 10% of the typical spray volume. Given that this crop can be sprayed more than 100 times before harvest, this represents significant savings in pesticides and refill time.

Special thanks to Syngenta Canada for providing lunch, to C&R Atkinson Farms Ltd. for hosting, and to Dr. Sean Westerveld, Dr. Melanie Filotas and Megan Leedham for contributing to the workshop.

About Sean Westerveld

Ginseng and Medicinal Herbs Specialist, OMAFRA
This entry was posted in Ginseng, Ginseng Meetings, Ginseng Other, Ginseng Pest Management, Ginseng Production and tagged , , . Bookmark the permalink.

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