Speed Doesn’t Kill Part 3: Economics

spray rig pictureThere has been a lot of research focusing on spray rig speed and spray coverage. Work by Jack Dibble back in the 70s-90s indicated that the best coverage is achieved at 1.5 MPH, and was the basis of the compromised recommendation of 2.0 MPH. This work has since been repeated by Dr. Joel Siegel (along with several collaborators) and Dr. Ken Giles and colleagues at Arbuckle, CA, and has indicated that at higher speeds, control of navel orangeworm (NOW) is lost in the upper canopy of the tree (>15′ high). This, interestingly enough, is where the majority of the crop is located. A few articles have been posted on this in the past (Speed Doesn’t Kill, Speed Doesn’t Kill, part 2).

In discussions about spray rig speed and hull split times, many people complain about how much time it would take to get across a field at 2 MPH and the cost of the practice. In calculating the numbers, there does appear to be some savings, but probably not as much as one would expect. In the table below, 5 speeds are listed and indicate how much ground they could maximally cover in an hour. This does not include fill up or turn around times. This estimate was used to calculate how long  (hours) it would take to spray 40 acres. The difference between 2 MPH and the other speeds was calculated, and multiplied by $27/hour (salary and benefits). This money “saved” was then divided over the 40 acres to get the amount of $ “saved”/acre.

Speed (MPH) Feet/hour Trees/hour (16’x22′) Time to Spray 40 acres Money “Saved” @$27/hour Money “Saved” /Acre
2 10560 660 7.45
2.25 11880 743 6.62 21.6 0.54
2.5 13200 825 5.96 40.5 1.01
3 15840 990 4.97 67.5 1.69
3.5 18480 1155 4.26 86.4 2.16

When looking at the numbers, the calculations indicate that only $2.16/acre are saved when spraying at 3.5 MPH versus 2.0 MPH. Assuming a 2500 lb/acre crop, this is the equivalent of reducing NOW damage at the lower speed  by 0.04%, or 1 lb/acre. Considering that work by Ken Giles and colleagues has indicated that increasing speed from 1.8 MPH to 2.4 MPH increases NOW survival by 8.7% in the upper canopy, its not too far out of line to think that a 0.04% reduction in NOW damage can be obtained at 2.0 MPH v.s 3.5 MPH.

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4 thoughts on “Speed Doesn’t Kill Part 3: Economics

  1. From Franz Niederholzer:

    “I’ll bet that a big contributor to faster ground speed is shorter time to get across big fields when spray windows are narrow. Still, the answer might be buy another sprayer. If you have 100 acres producing 3000 lbs per acre at $2.5 that’s a gross of $750,000. One percent worm damage = $7500 in lost nuts. More damage = more lost nuts plus, eventually, quality premium losses — depending on your marketer/processor. While, new engine requirements mean more costs in tractors, at today’s prices, quality pays, and it might pay to expand equipment?”


  2. Thanks, Franz. I agree – the time it takes to get across the field is crucial in the short window we have to apply hull split sprays – especially since farmers have to go every row.

    I think it would be nice to know at what speed with what equipment does control break down – in other words, would not spraying have a larger net income than spraying at 3.5 mph with 80 gallons of water using an airblast?

    David


  3. Hi David,
    We have also come to the same conclusion here at the Almond Board of Australia after two years of field evaluations of PTO and engine driven airblasts. Whilst there is more to spraying efficiency than just speed, after testing 3.5kph (2.2mph), 5.5kph (3.4mph) and 7.5kph (4.7mph), the 3.5kph treatments always came out best.
    Keep up the good work!
    Cheers,
    Brett



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