Spray mixing adjustments for apple thinning – May 25, 2021

How to adjust between parts per million, ounces, tree row volume and more.

Apple orchard
Photo by Anna Wallis, MSU Extension

When it comes to apple thinning, it can be a challenge to determine the actual volume of a product to include in a tank mix. Rates are typically recommended in parts per million (ppm), but there are many factors that influence how much product is delivered to the tree. Products usually also have a recommended rate in “ounces (oz) per 100 gallons,” which is easy to measure based on a 100-gallon dilute application. However, it doesn’t account for changes you may need to make based on tree canopy size, tank volume, spray concentration or adjusting nozzle pattern. Below are a few recommendations for how to adjust for these factors.

Recommended ppm and oz equivalents for NAA (PoMaxa)


Oz per 100 gallons dilute tree row volume (TRV)







The adjustments given below are based on a desired 7.5 ppm application of NAA, starting with a 3 ounce application per 100 gallons.

Adjusting concentration

Plant growth regulators (PGRs) should be applied at 1X dilute tree row volume (TRV). If applying at a greater concentration, still put the same amount of product in less water.


Water volume

Amount of NAA


100 gallons

3 oz


50 gallons

3 oz

Adjusting TRV

If tree canopy is greater than 100 gallons dilute, amount of water must be adjusted. The amount of product should also be adjusted proportionately to apply the same rate to cover the canopy. Below are adjustments starting with the 4 ounce rate of NAA for 100 gallons dilute TRV (equivalent to 10 ppm recommendation).


Amount of NAA

100 gallons

4 oz

150 gallons

6 oz

200 gallons

8 oz

Adjusting nozzle pattern

PGRs should typically be applied using a spray pattern in which two-thirds of the product is directed to the top half of the canopy, one-third to the bottom. However, in some cases, all the spray should be directed to the top of the canopy, such as when there is frost damage and a much heavier bloom in the tops of trees.

When you turn off the bottom nozzles to direct all the spray to the top of the canopy, you are also applying less water. Therefore, less product is also being applied. In this case, you should adjust the amount of product added to the tank mix to compensate.

Nozzle pattern

Amount of product

Amount of NAA

All nozzles on

100% recommended

3 oz

Bottom 1/3 off

130% recommended

4 oz

Bottom 1/2 off

150% recommended

4.5 oz

More guidance on calculating TRV and tank-mixing can be found in the 2021 MSU Tree Fruit Management Guide E-154 from Michigan State University Extension, and in these articles on Spray Mixing Instructions Considering Tree Row Volume from Cornell University and Spray Mixing Instructions from the University of Massachusetts.

Thanks to Jon Clements, Extension educator in commercial tree fruit production for UMass Amherst, for initiating this conversation and providing guidance.

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