Pennsylvania Tree Fruit Phenology Report: April 14, 2026

Peach Phenology and Late Freeze Damage on April 8^th 2026.

Peach flowers across Pennsylvania experienced significant injury following a spring freeze event that coincided with a wide range of developmental stages (Table 1). In southern regions of Pennsylvania, many blocks had already reached petal fall, while in central parts of the state, orchards were closer to first pink.

Within individual farms, variability in damage was also evident. Blocks situated at different elevations showed contrasting levels of injury, likely due to cold air drainage and temperature inversions during the freeze event. Lower-lying areas would have experienced colder conditions, resulting in higher levels of bud or flower mortality, while higher elevations may have escaped the most severe damage. In addition to these site-specific factors, inherent genetic differences among varieties likely played a role in determining survival rates.

The cumulative effect of winter injury followed by spring freeze damage further compounded losses in many orchards. Winter conditions had already reduced viable bud numbers (Figure 1), and the subsequent frost event added another layer of stress, leading to substantial flower kill in some locations.

Despite this, not all blocks experienced complete crop loss. In situations where flower survival exceeds 50-60%, growers should still consider implementing thinning programs. Even after significant environmental stress, surviving fruitlets can set heavily enough to warrant thinning to ensure adequate fruit size and quality.

Blossom Thinning Peaches with Accede

Following the freeze event, orchards across the state show a wide range of injury levels depending on both phenological stage and site conditions at the time of exposure. Careful assessment is essential before making thinning decisions.

Evaluate flowers by cutting buds or blossoms longitudinally and checking for browning or blackening of the pistils or ovules, which indicates tissue death (Figure 2). Avoid forcing shoots in water, as damaged flowers may still open but often fail to set fruit.

After estimating viable flower survival, adjust Accede™ rates accordingly. The labeled rate is 300–600 ppm (10–20 oz per 100 gallons per acre), with ~15 oz (≈450 ppm) per 100 gallons per acre as a standard reference under typical conditions. In blocks with reduced crop potential, lower rates should be considered, particularly in young trees, sensitive varieties, or where bloom density is already limited.

Accede™ can be applied from pink through petal fall, allowing flexibility after damage assessment. In blocks with moderate survival, some level of thinning may still be required, while severely affected blocks may not need any thinning. Please refer to the Penn State Extension article on Accede use for thinning in peaches including variety susceptibility and other considerations.

Weekly Summary Peach Bloom Phenology Data

Table 2 provides the complete observations for peach bloom phenology in the three counties where data was collected.

Apple Phenology and Late Freeze Damage on April 8^th 2026.

During the April 8^th freeze event, temperatures at many locations dropped lower than both forecasted values and readings from nearby weather stations. For example, the Rock Springs weather station recorded a low of 17°F, whereas on-site sensors placed within apple blocks measured temperatures as low as 12°F — a difference of about 5°F. This highlights the substantial within-orchard and between-orchard variability that can occur during radiation freeze events, largely driven by differences in elevation, cold air drainage, and site-specific characteristics.

As with peaches, apple bud survival varied depending upon location, variety, and phenological stage (Table 3).

Upcoming Weather and Blossom Thinning Recommendations

Across Pennsylvania, the upcoming week is expected to bring a rapid transition to very warm conditions, with daytime highs climbing into the low to mid-80s °F through midweek, followed by a sharp cool-down early next week, with temperatures dropping back into the 50s and even the mid-30s °F at night. There is also potential for intermittent thunderstorms and cloud cover midweek, before cooler and more stable conditions return.

Following the recent freeze event, apple orchards across Pennsylvania are likely to show variable flower survival depending on the stage at the time of the freeze, site elevation, and cultivar. Careful assessment of king and lateral bloom viability is essential before initiating any thinning program, as frost-damaged flowers may already reduce crop load. Where sufficient bloom remains, blossom thinning can be used to manage crop load early, especially in varieties such as Gala.

A key strategy this season is to delay applications until lateral flowers have had sufficient opportunity for pollination, particularly in blocks where king bloom may have been compromised by the freeze. This approach helps preserve remaining viable fruit set and reduces the risk of unnecessary crop loss. Targeting caustic thinners at approximately 60–80% bloom provides a practical balance, ensuring that lateral flowers are largely pollinated even if king blooms have been damaged or lost, while still allowing effective thinning of excess set. Caustic thinner option recommendations include:

1. Lime sulfur + oil: Apply ~2% lime sulfur + 2% oil at 60–80% full bloom.
2. Ammonium thiosulfate (ATS): Apply at 2.5–3% around ~60% full bloom.

Plant growth regulators (PGRs) can be used at full bloom:

1. NAA (naphthaleneacetic acid): ~10 ppm (~2–4 oz per 100 gallons) at full bloom
2. NAD (Amid-Thin W): ~35–50 ppm (~4–8 oz per 100 gallons) at full bloom

These PGRs are generally less aggressive, making them better suited for fast, compressed bloom periods where precise timing of caustic thinners is challenging.

Weekly Summary Apple Bloom Phenology Data

Table 4 provides the complete observations for apple bloom phenology in the three counties where data was collected.

Reference Information

Growing Degree Day Accumulation

Critical Temperatures References

The evaluations above reference bud stages for peaches and apples. The Penn State Extension article "Orchard Frost - Critical Temperatures for Various Fruits" lists in tabular format the temperatures at which 10% and 90% bud kill is to be expected after 30-minute exposure at each stage of development, and discusses a few of the reasons for deviations from the averages. To be concise, charts from Utah State University are included below in two figures that include photographs of the bud stages in addition to the critical temperatures.