2024 Champlain Valley 10-13mm Thinning Recommendations

Dr. Terence Robinson and Mike Basedow

Below is a review of recommendations from our virtual Fruit Set Meeting that we held on May 28th.  The recording of which can also be viewed below:

Assess each block for flower damage, set, and thinning achieved so far.

Depending on how your orchard was impacted by the cold, and your bloom and petal fall thinner applications, some blocks are more in need of a 12mm application than others. We think blocks that received ATS at bloom are probably closer to their targeted crop load, and may not need additional thinners.  Other blocks, such as Gala, still have plenty of healthy laterals, and will need to be hit hard at 12mm.  Assess each variety closely to come up with your best strategy.

Apply your thinners when king fruits are 10-13mm. You can also use the NEWA  carbohydrate model degree day calculator to target the best time for thinning. The 10-13mm thinner spray timing generally falls to when DD accumulations after full bloom are between 200-250 DD.  

In Peru, the 10-13mm thinning window is likely Sunday May 26-Thursday May 30 for Macs, and Honeycrisp the 28th through the 3st. Below is the current output from Peru with a Mac Full Bloom date of 5/13. Given the variability of bloom dates by variety and farm, we strongly encourage you to look at the carbohydrate model for your area with your bloom dates.

At 10-13mm, all thinners have a strong effect and are thus effective but also risky. Use the carbohydrate model to adjust your timing and rates.  We believe the heat last week likely will give us some natural thinning, in addition to whatever thinning we got from our petal fall applications last week.  This week things are turning in the other direction, and we are expecting a strong carbohydrate surplus during the 12mm thinning window.  We expect this will give very mild thinning conditions, and full rates, along with surfactants, will be necessary in blocks where we know we need a lot of additional thinning.  

Here are our full rate recommendations for select varieties. 

• Honeycrisp – use NAA at 3 oz TRVD basis + 1 pt Sevin XLR
• McIntosh – use NAA at 2 oz TRVD basis + 1 pt Sevin XLR
• Empire – use Maxcel at 64 oz TRVD basis + 1 pt Sevin XLR
• Macoun – use NAA at 4 oz TRVD basis + 1 pt Sevin XLR
• NY-1 and Gala – Maxcel at 64 oz TRVD basis + 1 pt Sevin XLR
• Cortland – use NAA at 2 oz TRVD basis

This is a year where you might want to add in a surfactant to increase your thinners’ efficacy.

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 3 oz NAA X Conc factor of 2=6oz NAA/100 gal X 5 for a 500 gallon sprayer=30 oz/sprayer tank
• Example 64 oz Maxcel X Conc factor of 2=128oz Maxcel/100 gal X 5=5 gallons Maxcel/sprayer tank

This might be year to concentrate your Sevin where you would like to achieve additional thinning when trees receive additional rewetting. Do not use concentration factor adjustment for surfactants.

Nozzle the sprayer differently for the next sprays

1.For the 12mm spray, nozzle so that 75% of the spray is directed to the top half of the tree.

2.For 18mm (if needed) only spray the top of the tree.

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