Pruning plus Calibration equals Coverage

So, a non-farmer buys a mature, highbush blueberry operation. The seller (a 30-year veteran) advises spraying as much, as often and as hard as possible. The nouveau farmer does so, albeit with reservations about wielding chemistry like a sledgehammer rather than as a surgical part of integrated pest management. The result? Spotted-wing drosophila (SWD) makes a mess of the operation and no one is comfortable with the aggressive pesticide use in a U-Pick operation.

The nice part about working with someone like this is that they have no preconceived ideas and they are willing to make big changes 🙂

The first thing they did was perform an aggressive pruning (see image below). This has many benefits:

  • Allows air to circulate and humidity to escape, reducing potential for disease.
  • Improves light penetration, which improves berry quality.
  • Clears alleys of overhang, allowing the tractor to pass without damaging berries or blocking spray nozzles.
  • Exposes the lower-middle portion of the canopy, where SWD is known to reside when it is hot and dry.

If you can see a little light through a post petal-fall canopy at high noon, you have done a good job of pruning.

Yes, this has an economic impact. There’s less production per acre, and trellising the bushes may become necessary as berries weigh the bush down. However, the owner noted that the quality of the remaining berries was greatly improved, and this meant fewer hours culling berries during packing. He felt he came out ahead.

But what about the sprayer? As further incentive to purchase the operation, the exiting farmer included his ancient Kinkelder air shear sprayer (see below). This old monster might have been ideal when trying to reach the top of standard fruit trees, but the >100 mph air and Extremely Fine spray quality it produced was beyond excessive for a berry operation. We’ll say it was “dramatic”.

The new owner toyed with purchasing a cannon-style sprayer in the hopes of spraying multiple rows in a single pass, but given his desire for improved coverage and reduced waste, he elected to go with an axial sprayer and spray every row more economically. It then remained for us to calibrate the air volume, air direction and travel speed before settling on a nozzling solution. This process is covered in many articles found here and in the Airblast101 book.

In April, May and June we used water-sensitive paper confirm coverage. Regular scouting has been ongoing, and we will post the results in this article after harvest. By matching the sprayer calibration to a well-managed canopy, the operator has gone from 1,000 L/ha to ~400 L/ha, representing considerable savings in water and pesticide. Chemistry is rotated and applications are made according to IPM in early morning (as long as there are no pollinators) to avoid potential drift due to thermal inversions. The following image shows what those papers looked like in June.

The following video shows very little spray escaping the target rows. Bear in mind the wind was very high, but given that this was just water we saw it as an opportunity to test in a worst-case scenario (please don’t spray in such high winds). We used air-induction hollow cones in the top nozzle position so droplets were large enough to fall back to ground when they vectored over the top of the canopy, or between the bushes. Further, the air produced by the sprayer was moderate enough that we anticipate reduced “sand blasting” of the berries, or fruit blown off the bushes.

The grower is very happy with the reduction in noise and the greatly improved accuracy of the spray applications. By early July, berries looked great (see image below) and spray coverage continued to meet threshold without excess. Note in the following image from a July 1st application that spray coverage is highly variable; Occasionally there are drenches and misses. This is why it is important to assess coverage in multiple locations an not rely on a single target canopy.

This article will continue to grow as the season progresses. Stay tuned.