2025 Capital Region Petal Fall Thinning Meeting Summary
Terence Robinson and Mike Basedow
Below is a review of recommendations from our Petal Fall Meeting that we held virtually on May 12th. The recording of which can also be viewed below:
Bloom quality has generally been very good through the Capital Region in 2025. In Mike’s visits to orchards on Friday:
- Bloom appears very good in most varieties. An occasional Honeycrisp and Fuji block might be looking light, with tree to tree variation
- A few occasional kings were missing in some low lying Honeycrisp blocks. This was less than 10% of flowers observed though, and laterals look healthy across the board.
One caveat that we should consider is that we’ve haven’t had very good pollination weather throughout the bloom period. Before applying your petal fall thinners, look closely at your fruitlets, and look for initial indications that fruitlets are setting. Look for obvious growth within the kings, healthy green stems, and fruitlets starting to hook upwards along the cluster, rather that drooping down.
If you are feeling confident about your initial set, and want to get some thinning done at petal fall, we should have a very good thinning window over the next few days.
Wait until king fruits are 5-6mm before applying your petal fall thinning spray. Spray your petal fall thinners when DD after full bloom are between 100-130 DD base 4C. We expect the main petal fall thinning window in the Clifton Park area to fall around Wednesday May 14 – Friday May 16. This will be a few days later in more northern and western portions of the Capital Region. To double check your window, enter your full bloom dates into the apple carbohydrate model.
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 significant deficit this week to help achieve very good thinning.
This should come with some caution though:
- Check the model the day you plan to thin
- Look at the 6 day average carbohydrate deficit
- If the 6 day deficit is at -60 or more negative, we recommend holding off on thinning until it comes back up
- If the 6 day deficit is above -60, we recommend adjusting your rate according to the model, to prevent any potential for overthinning under this deficit
Rate recommendations for this timing:
- 7.5ppm (3-4oz) NAA per 100 gallons dilute TRV + 1 pt/100 of Sevin on Honeycrisp,
- 7.5ppm (3oz) NAA per 100 gallons dilute TRV with no Sevin for Cortland
- 100ppm (64 oz) Maxcel per 100 gallons dilute TRV + 1pt Sevin/100 for Gala, Snapdragon, and Empire
- 5ppm (2oz) NAA per 100 gallons dilute TRV + 1pt/100 of Sevin on McIntosh
- Do not thin Evercrisp at petal fall. Instead, wait until 10mm to thin this variety.
Surfactants like Regulaid can increase the response of NAA. We are expecting a carbohydrate deficit, so a surfactant will likely not be needed in for the petal fall thinner application in the Capital Region this year.
- 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.