Speed Doesn't Kill Part 3: Economics

There 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.