2024 Capital Region Petal Fall Thinning Recommendations

Posted on by mrb254

2024 Capital Region Petal Fall Thinning Recommendations

Dr. Terence Robinson and Mike Basedow

Below is a review of recommendations from our Petal Fall Meeting that we held virtually on May 13th. The recording of which can also be viewed below:

Assess each block for flower damage.

We found variable damage throughout Saratoga county when evaluating orchards on Monday May 13th.  While there is much variability, and your mileage will vary, Honeycrisp and NY-1 had less damage than Gala, and Mac types like Mac, Cortland, and Macoun had the most.  Honeycrisp and NY-1 were missing a few kings, Gala were missing a few more kings, and the Mac types were sometimes missing many kings and some laterals.  While we think there are still many laterals and thinning to be done at petal fall, the best way to know is to assess your own blocks carefully, and adjust your thinning accordingly:

  • If most king flowers are present, use full rates and follow the carbohydrate model.
  • If king flowers are damaged, then thin with lower rates.
  • If kings and laterals are damaged then don’t thin until 10-12mm.

Wait until king fruits are 5-6mm before applying your petal fall thinning spray. You can also use the NEWA  carbohydrate model degree day calculator to target the best time for thinning. Spray your petal fall thinners when DD after full bloom are between 100-125 DD.  

At Clifton Park the petal fall thinning window will likely be Sunday May 12-Wednesday May 15. At locations further north, or at higher elevation, this will likely be a few days later, likely nearer to the end of the week.

At petal fall, all thinners have a moderate effect and are thus very safe. (There is little risk of over-thinning). The caveat would be to not spray when carbohydrate deficits are -60 or less. With the weather forecast we currently have, the carbohydrate model indicates there will be a moderate deficit this week to help achieve good thinning.

Use full rates where set is good:

  • 7.5ppm (3-4oz) NAA + 1 pt/100 of Sevin on Honeycrisp,
  • 7.5ppm (3oz) NAA with no Sevin for Cortland
  • 64 oz Maxcel/100 + 1pt Sevin/100 for Gala and Snapdragon and Empire
  • 5ppm (2oz) NAA + 1pt/100 of Sevin on Evercrisp and McIntosh

Surfactants like Regulaid can increase the response of NAA.

  • If there is no carbohydrate deficit, include a surfactant
  • If there is a carbohydrate deficit do not include a surfactant.

Suggested rates are dilute TRV rates. Calculate TRV for each orchard and then a concentration factor:

  • TRV/Volume of spray per acre=Concentration factor
  • Example: TRV=200 and spray volume is 100 then concentration factor=2

Multiply suggested rates by concentration factor to get rate/acre.

  • Example 3oz NAA X Conc factor of 2=6oz NAA/100 gal X 5 for a 500 gallon sprayer=30 oz/sprayer tank

If you use concentration factor for adjusting rate of Sevin then rains will increase the effect of the Sevin. Do not use concentration factor adjustment for surfactants.

Nozzle the sprayer for the petal fall spray with 1/3 of output to the bottom half of tree and 2/3 of the output to the top half of the tree.

Questions? Please feel free to reach out to Mike at mrb254@cornell.edu or 518 410 6823.