The response to hormone-based thinners is a function of the amount of product that is deposited on the tree leaves. So, the more product you apply per acre the stronger the thinning response you will get. Now this gets confusing when we talk about actually amounts of products and concentrations of solution. A spray at a high concentration (e.g., 100 ppm) versus one at a low concentration (e.g., 1 ppm) if applied at the same volume per acre (e.g., 200 gallons) will result in the high concentration spray depositing more actual product in that acre than the low concentration spray. However, if you change the volume you are applying per acre, it is possible that even when you are doing a high concentration spray you could end up applying less actual product per acre than if you apply a high volume at a low concentration. For example, if you apply 1000 gallons per acre at 1% solution this will be more actual product applied per acre than if you apply 50 gallons per acre at 10% solution. The bottom line is that the actual amount of total product you are applying per area is very important.

So, how do we estimate the actual amount of product (e.g., Maxcel, NAA) per acre we need to apply? The first thing we need to determine is how much is the total volume of solution (water plus product) we need to apply. The total water volume needed to spray the tree canopy to the point of runoff is referred to as the Tree Row Volume (TRV) or sometimes you may also see this as dilute TRV. Here’s the formula on how to calculate TRV for your orchard block:

TRV = (Tree height X Tree width X 43,560 X 0.7) / (Between row spacing X 1000).

Example: A mature Honeycrisp Tall Spindle orchard planted at 4’X12’spacing with trees reaching 1’over the 10’ top wire. The calculation for the TRV is (11′ X 8′ X 43560 X 0.7) / (12′ X1000) = 223 gallons/acre (rounded to 200GPA).

Now, this is the part that is critical, the recommendations for thinners are usually based on 100 gallons of TRV (e.g., 48oz of Maxcel per 100 gallons), which means this recommendation is based on a theoretical block that would require 100 gallons of water to get the tree canopy to the point of runoff. However, if you block requires 200 gallons to get the point of runoff, you need to put double the amount of product (in this case 96 oz of Maxcel).

Okay, now you have calculated the total amount of product you need to apply per acre based on the size of the trees, which in our example is 96 oz of Maxcel for a block that requires 200 gallons of water to get to the point of runoff. However, do you need to apply your product to the point of runoff? No, you can choose to apply less volume of water and not get to the runoff point, but you still need to apply the 96 oz of Maxcel per acre.

You are probably asking yourself how do I decide how much volume of water I should apply? My recommendation is to use a total volume of water that will ensure a good coverage which in high density orchards tend to between 75 to 100 gallons per ac.

Here’s a link with other resources that also explain how to calculate TRV (also referred to as dilute TRV or dilute volume):

Tree Row Volume: What it is, why it matters and how to use it.

Rates of NAA and Maxcel based on different TRV (also referred to as dilute gallonage or dilute volume).

Spray Mixing Instructions Considering Tree Row Volume – TRV

Sprayer Calibration Worksheet

This article was posted in Apples and tagged Amaya Atucha, Apples, thinner sprays, Tree Row Volume, TRV.