Freeze-damaged Gala flowers and fruitlets at Rock Springs. Photo by Lindsay Brown, Pennsylvania State University.

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Assessing the Damage

Southern Pennsylvania is in for a cool week ahead with temperatures remaining below seasonal norms and highs struggling to reach the upper 50s. These conditions are likely to slow tree development and fruit growth, making it difficult to visually assess whether fruitlets are sizing and progressing normally following the April 21 freeze event, as subtle differences in growth between damaged and healthy buds can be easy to miss.

Growers should consider tagging representative king and lateral bud clusters and checking them at regular intervals over the coming week to more reliably track fruitlet development and distinguish between buds that are recovering and those that sustained freeze damage without yet showing obvious symptoms. As confidence in primary fruit set improves, typically around the 10 mm stage, thinning decisions can be made with greater accuracy and confidence.

Most growers can take this week to assess fruit growth, with thinning decisions likely coming towards the end of the week or early next week as fruit moves into the 10 to 15 mm (roughly ½") size range given current growing conditions. Toward the weekend, if growers are considering a light thinning, applying about a pint to a quart of carbaryl per acre can help loosen clusters slightly.

When both primary and secondary bloom have survived, thinning decisions should focus on optimizing fruit quality while managing uncertainty in crop load. A careful, block-by-block assessment of fruit set is essential, distinguishing between primary fruit and those from secondary bloom.

Primary fruit typically set earlier, have stronger vascular connections, and produce larger, more uniform fruit, so they should be prioritized for retention. Secondary fruit can serve as early insurance if the primary set is questionable, but they often lag in size and maturity and can reduce overall fruit quality if too many are retained.

If assessments this week indicate that enough primary fruit have survived, a lime sulfur application can be used to selectively target secondary bloom (Figure 1), with a recommended rate of 2% lime sulfur combined with 2% stylet oil (1.5% is also fine), providing an effective early thinning option before committing to more aggressive chemical thinning programs.

The photo depicts Honeycrisp secondary bloom at the full pink stage. — **Figure 1.** Secondary bloom on Honeycrisp at Rock Springs in Centre County. Photo by Lindsay Brown, Pennsylvania State University.

Centre County and the Central Susquehanna Region

The freeze on April 20–21 impacted Central Pennsylvania when varieties were transitioning from full bloom to the petal fall stage (Figure 2).

The photo depicts two flower clusters. On the right is a primary cluster than has been killed by frost. On the left is a secondary cluster than may produce a crop. — **Figure 2.** A Honeycrisp secondary cluster at the late pink stage adjacent to a largely non-viable primary cluster, where both the king bloom and lateral flowers were killed. Secondary bloom in such cases may provide some compensatory fruit set; however, these fruit typically lag in development, are more variable in size and maturity, and should be managed carefully during thinning to maintain overall fruit quality and uniformity. Photo by Michael Rocinante Evans, Pennsylvania State University.

Following assessment of the April 21 freeze event, damage across primary bloom has been significant and near total across varieties (Table 1). Honeycrisp has fared the worst, with both primary king and lateral buds confirmed dead and no secondary bloom initiating to offer any recovery potential. Gala, Pink Lady®, and Fuji show a similar pattern of primary king and lateral loss, with a few secondary live blooms at pink. Golden Delicious stands out as the most encouraging, with primary kings lost but at least one live primary lateral confirmed, and importantly, secondary bloom is now beginning to develop, offering some potential for crop recovery. Given that secondary bloom is initiating in Golden Delicious, a streptomycin spray is being planned for today and Friday to protect against fire blight infection through these late-opening secondary flowers.

**Table 1.** Mortality Estimation from the April 21 Freeze (One Week Post-freeze Event.)
Variety	Primary Bloom		Secondary Bloom
	No. of Fruits	%-age Survival	No. of Flowers	%-survival
Cortland	83	31 %	-	-
Evercrisp	67	36 %	72	99 %
Gala	100	15 %	61	90 %
Honeycrisp	123	24 %	100	97 %
Jonagold	92	15 %	-	-
Macintosh	100	19 %	-	-
Pink Lady®	73	45 %	55	91 %

Berks County

Berks County apples have just arrived at the post-bloom / fruitlet stage (Table 2). Crop assessments are being conducted but not ready for publication.

**Table 2.** Apple phenology observations from Berks County.
Variety	Stage
Fuji	Post-bloom
Gala	Post-bloom
Golden Delicious	Post-bloom
Honeycrisp	Post-bloom
Pink Lady®	Post-bloom
Red Delicious	Post-bloom

Adams County

Apples

Except for Golden Delicious and Pink Lady®, we followed the fruitlets measured last week (Table 3). In the last few days Aztec® Fuji king fruitlets were those that grew the most (0.76 mm/day) while RubyRush™ grew the least (0.23 mm/day). The other varieties had an average daily growth for king fruitlets of 0.54 to 0.63 mm. As expected, the lateral fruitlets randomly selected (and presumed healthy) are growing slower than the kings and they range from 0.23 mm/day for RubyRush™ to 0.51 mm/day for Aztec® Fuji. We need to keep monitoring fruitlets diameters and growth to better assess the damage due to cold snap.

**Table 3.** Phenology data for Adams County apples as measured at the Fruit Research and Extension Center in Biglerville. The selection of the king and laterals was random along the rows just avoiding the yellow-pedicel fruitlets that are about to fall. (*) indicates that it was difficult to find healthy kings to measure. In all measurements, n=20.
Variety	Stage	King Diameter	Lateral Diameter
Evercrisp® (MAIA1)	90% petal fall	6.12 *	4.62
Fuji (Aztec®)	100% petal fall	7.19	5.66
Gala (Buckeye®)	100% petal fall	6.7	5.74
Golden Delicious	100% petal fall	7.35	5.97
Honeycrisp (Premier®)	90% petal fall	6.29	4.76
Honeycrisp (Royal Red®)	100% petal fall	6.77 *	5.72
Pink Lady®	95% petal fall	3.85 *	5.72
RubyRush™ (NJ150 cv.)	95% petal fall	6.33	5.43

Healthy growing fruitlets at this stage (11 days after full bloom (DAFB) for FREC horticultural blocks) could grow even more than 1 mm/day. It is known that slower growing fruitlets (0.25-0.30 mm/day) are more likely to abscise in the next few days (Greene et al., 2013; Hillmann et al., 2025). The loss of healthy kings may lead to a crop set on the best lateral (Figure 3).

The figure depicts a cluster of five fruitlets on a bud of the variety Pink Lady®. The king fruit has clearly been killed by the frost, with the color of the pedicel changing to a light yellow from its normal green coloration. Among the cluster are three later fruitlets that appear healthy, which may be useful for setting a crop. — **Figure 3.** Pink Lady® apple at FREC on April 27^th. The red circle highlights the cluster with the weak, yellow-pedicel king fruit that is about to drop and at least three good laterals actively growing. Photo by Dr. Sara Serra, Pennsylvania State University.

Citations

Greene, D. W., Lakso, A. N., Robinson, T. L., & Schwallier, P. (2013). Development of a Fruitlet Growth Model to Predict Thinner Response on Apples. HortScience, 48(5), 584–587.

Hillmann, L., Gonzalez Nieto, L., Kon, T., Larson, J., Musacchi, S., Robinson, T., Serra, S., & Einhorn, T. C. (2025). An Apple Fruit Set Prediction Model From Distributions of Fruitlet Mass Accurately Estimates Abscission in Four Disparate Regions of the United States. HortScience, 60(11), 2007–2017.

Pears

The April 27^th caliper measurements in the Harrow Sweet block resulted in an 11.7 mm mean diameter (n=20). In that block there was a survival of 57% of the pears after the mortality assessment conducted following the April 21st cold event. In some of those pears, a frost ring is already evident at the calyx base (Figure 4). Yellow-pedicel and cold-damaged fruitlets started dropping on the 27^th.

The cluster of five pear fruitlets appear to be healthy, but the king fruit was hit by the freeze after the fruitlet had set. The result is a ring of russeted tissue on the distal end of the fruit. As the pear matures, the frost ring will have russeted epidermal tissue, easily detected by touch. — **Figure 4.** Harrow Sweet pear at FREC on April 27^th. The red circle highlights the frost ring on the calyx end of the pear. The average pear diameter (n=20) is 11.7 mm as of April 27^th. Photo by Dr. Sara Serra, Pennsylvania State University.

Reference Information

Growing Degree Day Accumulation

Current growing degree days for Adams, Berks, and Centre counties are provided in Table 4.

**Table 4.** Growing degree days for the regions represented in this report. Data was taken from NEWA using the Degree Day Type of "Base 41˚F", "Base 43˚F" and "Base 50˚F" between the dates of 1/1/2026 and 4/27/2026.
County	Weather Station	Base 41°F	Base 43°F	Base 50°F
Adams	Biglerville (Penn State FREC)	729	623	347
Berks	Boyertown	637	542	296
Centre	Rock Springs (Penn State)	573	487	256

Critical Temperatures References

The evaluations above refer to apple bud stages. 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, a chart from Utah State University is included below in Figure 5, which shows photographs of the bud stages in addition to the critical temperatures.