Initial fruit set is unsettled for some orchards in the southeastern US. This is largely due to challenging weather conditions for pollinator activity during the bloom period. Despite these issues, some cultivars/locations have strong initial fruit set (see Gala above).

Spring 2025 has been moving fast in western NC. It has been difficult to keep pace with the season for many. Several cultivars are at or past petal fall, while late blooming cultivars (Rome, Honeycrisp, CrimsonCrisp, etc.) still have a lot of open bloom.

Here is a brief summary of some factors that will influence crop load management decisions in NC, SC, and GA:

• Despite a “typical” green tip date for many locations (March 11th in Mills River, NC), the 2025 full bloom date on Gala (April 1st) was the earliest that we observed over the past 8 years (at least).
• Inconsistent return bloom was observed in several blocks / cultivars that are prone to alternate bearing. Red Delicious, Golden Delicious, Honeycrisp, and Fuji are the main offenders….
• The bloom period was relatively short due to warm weather. High winds, rain, and cloud cover during the bloom period limited pollinator activity. Some growers faced logistical challenges in getting hives into their orchards in a timely manner.
• Despite difficult conditions during the bloom period, there were some narrow windows of respectable weather for bee flight.
• We observed at least three events with risk of cold injury. In general, minor damage was observed across most locations. Based on all reports to date, the majority of our production area was not impacted significantly… though I suspect there are some frost-prone sites that have damage. I note that we are still a long way from the frost-free date.

Here is the primary takeaway message: Initial fruit set is variable this season and needs to be monitored in advance of making post bloom thinning decisions. This can only be done by repeated assessments and fruit diameter measures. 

We are entering the post bloom chemical thinning window. Over the next 4 days (April 18th to April 21st) high temperatures will be in the upper 70’s and low 80’s and will be sufficient for chemical thinner activity for all available products (> 68 F). As of today (04.18.25), there is a moderate carbon deficit predicted over the next 4 to 5 days for most sites in the region.

So what should I do?

To me, there are two different approaches for this upcoming thinning window. Both have merit. This is not “one size fits all” and will need to be determined on a case-by-case basis:

A. Drag your feet a bit. If fruit set remains unsettled or if fruit size is too small, then you should defer this decision until you see that fruit are growing and setting.

• What is the risk here? Unsettled weather next week may make successful thinner applications difficult next week, which will likely align with the 8 to 14 mm timing for many cultivars and locations. If thinning cannot occur next week, then it is possible that some fruit will be too large for typical post bloom thinning programs (>15mm fruit diameter). In this scenario, it is possible that some orchards will receive their 1^st thinner application during the rescue thinning window (18 to 24 mm).

B. Thin now while you know you have a window. If fruit set appears to be strong and fruit size is within range for a petal fall or post bloom thinner application (8 to 14 mm), then this may be a good opportunity to try to knock off some fruit. After Monday afternoon (04.21.25), weather patterns look unsettled and sketchy (rain/thunderstorms).

• What is the risk here? The carbon balance model is a useful tool that relies upon forecasted weather data. If forecast data is accurate, the carbon balance model output across most locations in the region suggests that normal thinner rates or a decrease in rates (by 15%) is suggested. This would indicate that trees are sensitive to chemical thinner at this time… which is generally a good thing.
• However, forecast data for cloud cover can be unreliable. If we observe multiple days of heavy cloud cover with warm temperatures, then this situation will change. Work by Ross Byers in the 1980’s (Virginia Tech) suggests that ~3 to 4 days of heavy cloud cover can lead to natural thinning.

Is there a way to predict chemical thinner responses faster than waiting 10 to 14 days after thinners are applied?

Our research team has been very active in this area over the past 5 years. There are several promising tools and technologies that we have evaluated to date. One tool that is ready for commercial use is the Fruitlet Size Distribution (FSD) Model, which was developed by Laura Hillmann and Todd Einhorn at Michigan State University. This model has been tested extensively in MI, NY, WA, and NC and has proven to be a useful in estimating fruit set following chemical thinner applications. Predictions can be made within 8 days of a chemical thinner application. If of interest, we suggest starting with a block or two to get familiar with the process and to determine if this is of benefit to you and your operation.

Below is a link to detailed user guide for the model (authored by Laura and Todd):

THE FRUITLET SIZE DISTRIBUTION (FSD) MODEL: A HOW-TO GUIDE

Here is the link for the XLSM file for the model. Please read HOW-TO-GUIDE above first. Note the XLSM file will need to be downloaded and run locally on your computer. (Click the Download icon in upper right after viewing FS Predict in Dropbox link above.) Macros have to be enabled.

Below is an early report of FSD model performance across 4 locations (pages 4 – 6):

Use Social Media for Positive Information on Fruit Farming

Acknowledgments

This work is supported by the Specialty Crop Research Initiative, project award no. 2020-51181-32197, from the U.S. Department of Agriculture’s National Institute of Food and Agriculture.

Additionally, this work is supported by The NC Specialty Crop Block Grant Program. The NC Specialty Crop Block Grant Program is supported by the NC Department of Agriculture & Consumer Services with funding from the US Department of Agriculture’s Agricultural Marketing Service.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and should not be construed to represent any official USDA or U.S. Government determination or policy.