Spraying: race with the calendar is won in pit lane

Timing trumps most things in crop protection.

A great spray applied at the wrong time isn’t nearly as valuable as a mediocre spray at the right time.

So how do we improve our ability to get things done at the right time?

We often try to win races by driving faster, but driving fast can lead to more drift and less uniform deposition.

Driving slower can be viewed as a sort of insurance policy. You may not notice the benefits right away, but on days when that extra bit of performance is required, you’re covered.

It turns out that productivity beats speed. We recently built a model to capture all the elements of a normal spray operation that affect timeliness:

  • travel speed
  • boom width
  • tank size
  • water volume
  • field length
  • number of headlands
  • turning speed
  • fill time

We first identified a reasonable base condition, which for the sprayer was a travel speed of 14 m.p.h., a 90 foot boom, an 800 gallon tank, a 10 gallon per acre water volume and a 20 minute fill time.

We set up a typical field situation, spraying a half-mile run on a quarter section with two sprayed headlands and a turning speed of 8 m.p.h. We changed one factor at a time to determine its relative importance.

Before we discuss the results, let’s make it clear that we’re not recommending certain factors just because changing them improved productivity. For example, adequate water volume remains an important input that improves coverage and permits the use of low-drift sprays. Larger tanks increase compaction and take more power.

For the base condition, the sprayer spent 15 percent of its driving time turning and 37 percent of its on-field-time stationary while it reloaded. Forty-eight percent of every hour on the field was spent spraying for an average productivity of 82 acres per hour.

Increasing to 18 m.p.h. increased average productivity to 93 acres per hour, but that increased the proportion of time spent turning and loading, resulting in 40 percent of the field time spent spraying.

Decreasing the loading time from 20 to 10 minutes reduced the amount of field time spent stationary to 23 percent, covering 100 acres per hour at 14 m.p.h. Sixty-two percent of on-field time was now spent spraying.

Boom width was important. A 33 percent increase in boom width from 90 to 120 feet boosted productivity to 94 acres per hour, close to the same result as increasing the travel speed to 18 m.p.h. Similar side effects occurred: more time turning and a greater proportion of time filling.

Boom width seems to have some room for growth. European countries tend to use wider booms than we do in Canada and with GPS guidance and large fields, we have excellent conditions for their implementation.

Using less water and larger tanks increased productivity by decreasing the fill frequency.

Decreasing water volume to five from 10 gallons per acre increased productivity to 100 acres per hour because it decreased the proportion of time the sprayer was stopped to 23 percent from 37. Increasing from an 800 to a 1,200 gallon tank increased productivity to 94 acres per hour and decreased filling time to 28 percent.

Taken together, a sprayer with a 120 foot boom and a 1,200 gallon tank that applied 10 gallons and filled in 10 minutes had an average productivity of 132 acres per hour at 14 m.p.h.

If you can string two quarters together and drive a whole mile before turning, that number rises to 145 acres per hour.

Other operating efficiencies can be found as well:

  • Prepare for the job by reviewing the product label in advance, noting the correct mixing order.
  • Keep extra nozzles, clamps and nozzle bodies in the cab.
  • Don’t clean plugged nozzles, replace them.
  • Use low-drift nozzles so an increase in wind doesn’t shut you down.
  • Ensure all the products needed are on the tender truck, such as pesticide, adjuvant, tank cleaner and anti-foamer.
  • Consider switching to three inch plumbing, which makes pump rates of 300 to 400 gallons per minute possible.
  • Make sure your inductor won’t be the limiting factor. For example, product pumps can be awfully slow when the product is cold. It might be worthwhile exploring a venturi system.

Speeding up the fill process is a good idea, but be careful with certain products. Dry materials such as the sulfonyl ureas (Refine, Express SG) and some fungicides (Astound) require time to hydrate in water so that they mix properly.

Consider time spent cleaning the sprayer.

So, the quicker we can spray, while ensuring a quality job, the more effective crop protection practices will be. We encourage you to use our productivity calculator to determine your best configuration. You can find it and lots of other sprayer-related resources on www.sprayers101.com.

Got a productivity tips to share? Let us know. And remember: in spraying, the race is won in the pits.

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