Chemical Thinning Assessments for Apples Made Easy
(From Joe Costante's files)

Finally, we have reached the stage, following four years of research trial and error, to reduce our fruit thinning assessment form for NAA use to one sheet of paper.  The system works fine and has proven very effective according to the feedback received.  Along with a reduction in paper work, we have also been able to cut the assessment process in half.  In fact, after completing a few orchard exercises, you should have the confidence to assess comparable orchards by completing only the five (A-E) form procedures.  Keep one important fact in mind when working the assessment - the suggested NAA rate arrived at is considered the mid-range point which you can either add ppms to or subtract from, depending upon crop potential and orchard tree vigor prior to application.

We urge you to keep a very close eye on fruitlet growth and development following Bloom, especially if ideal weather is experienced.  Following Bloom, check fruit diameter development frequently.  Remember that the thinning program should be initiated before lateral fruit diameters average 10 mm.
**More recent research has shown that the sooner after petal fall the thinning is done, the better the results and also it gives you a better opportunity to come back with a second application.
     It is our hope that you will make good use of the chemical thinning assessment packet.  If you need additional forms or have questions concerning thinning, please give us a call.

A Walk Through the Thinning Assessment Format for NAA

• Fill out the initial orchard information in the top section and be sure to record Days After Full Bloom (DAFB) - when the assessment actually takes place.
  
• The first order of business is to select and collect data from 5 typical, healthy trees within the orchard or block.  Procedure A says to estimate over each tree's canopy, the number of fruit (1 to 5) growing within the clusters.  Determine an average for each tree, than an overall average for the 5 trees and record it on the line provided.  Fill in the remaining 4 lines (B to E) with the overall averages requested.
  
• Procedure B has you determine the percentage of active clusters (those with growing fruit) over each tree's canopy and then determine and record an overall average for the 5 trees.
  
• Next, Procedure C says to select two typical fruit clusters from each data tree and measure the diameter of a lateral or side fruit  (the larger King fruit usually sits in the center of the cluster) in each cluster and, after repeating this process on the remaining 4 trees, determine and record the overall average fruit size based on the 10 measured apples.
  
• Procedure D has you cut the 10 measured apples in-half and assess their seed development.  Rate each apple as to whether it has 5 or more white creamy seeds and score 1.0 for each apple having this status.  Follow this procedure for each apple and if less than 5 seeds are found score 0.65 or a 0.25 for each apple without any seeds.  Then record the overall seeding average for the 10 apples.
  
• Last, Procedure E has you rate and average overall tree vigor in terms of canopy size and condition - leaf area, sizes, depth of green color, and health status.  Assess wood development, especially fruiting wood.  Tree vigor is usually easy to determine and it doesn't take long to get into a rhythm.
  
• The third section of the form deals with crunching some numbers to determine the final recommended rate for NAA application.  First (#1) you record the fruits/cluster average from A (from here on we will use example data throughout the form) 3.2 and multiply this by the percentage of overall active (growing) fruit clusters B .65 = 2.08 as the crop potential factor.
  
• Number 2 says to take the seeding factor recorded in D 1.0 multiply this by the crop potential derived in #1 2.08 which in turn is multiplied by 100 = 208 which is divided by 50 = 4.16 and represents the ppm factor.
  
• Now moving to Number 3, let's say our orchard is 20 years old so we then inject the factor 1.5 (note the age/factor groups on the form) and multiply it by the ppm factor derived in #2 4.16.  Then this answer is multiplied by the tree vigor average in E 90 = 5.62 which represents the suggested NAA (ppm) mid-range rate.  If you feel this is on the low side for your orchard conditions, than we suggest that you could increase the rate by 1.0 to 1.5 ppm (6.62 to 7.12) or conversely, if you feel it's too strong then reduce the rate by 1.0 to 1.5 (4.62 to 4.12).
  
• Now if you have encountered a problem(s) with the orchard as noted in the reduction section, it must be included in determining the final rate of NAA to be applied.  For example, if you had a light frost, we're suggesting that a 20% reduction adjustment be subtracted from the suggested mid-range rate derived in #3 (the same procedure should be followed for all reductions listed).  If any rate, after a downward adjustment, falls below 2.5 ppm then NAA is not worth applying.  Back to our example, now multiply the suggested rate of 5.62 by .20 = 1.13 which in turn is subtracted from 5.62 = 4.49 or (or 4.5) ppm of NAA which represents the final recommended rate to be applied.  Numbers should be rounded off to represent wholes and halves.  For example, 5.62 would become 5.5 and 5.83 would become 6.0 or 4.13 would be 4.0 and 4.4 would become 4.5 - just a matter of using common sense.
  
• The last section on the form deals with the number of days left to thin effectively or before fruit size has reached 14.0 mm.  To determine this date you merely record the fruit size average from C 9.3 mm and divide it by the number of Days After Full Bloom (recorded in the top section of the form) 12 = 0.78 mm which represents the average rate of fruit growth per day.  Now take the last effective fruit size for a thinner response 14.0 mm and divide it by the average growth rate per day 0.78 mm = 18 days to reach an average size of 14.0 mm.  The orchard is already 12 days into the growth process therefore, subtracting 12 from 18 leaves 6 more days remaining for effectively thinning with NAA.