Pennsylvania Tree Fruit Phenology Report: May 19, 2026

This will be the final phenology update for 2026. These have certainly been "interesting times" as the old proverb goes.

As we move through the season, Penn State Extension will keep you informed of any critical developments through the Fruit Times news/alert system. These are distributed using the same channels as this report, so should arrive automatically.

Normally, this is where a promotional blurb for the seasonal Apple Maturity Reports would go, reminding people to look for them to begin in late August. This is still the plan, though what those reports will look like cannot be known at this time. It may be a struggle to obtain sufficient fruit to test, particularly when every piece may be particularly valuable!

Before moving on to this week's report and recommendations, a note about the public roundtables being hosted by the Pennsylvania Department of Agriculture (PDA) in collaboration with the PennAg Industries Association. The first two roundtables were fact-finding in nature, giving growers the chance to discuss the condition of their fruit or lack thereof. Pennsylvania Secretary of Agriculture Russell C. Redding's office has confirmed that the date and time of the third roundtable has not been set at this time.

When details of this Zoom/call-in meeting become available, look for an announcement on the PDA website, where a red callout box has been placed to draw attention to these meeting. Furthermore, look for announcements from Penn State via any of the following: a Fruit Times Alert, the Dr. Tree Fruit and Don podcast, a message on the 1-800 PENN IPM system under the Tree Fruit > Events section, or direct email from The State Horticultural Association of Pennsylvania, the Young Growers Alliance, or the Adams County Fruit Growers association.

Phenology Report and Management Recommendations

Temperatures in Pennsylvania this week are expected to be quite warm to start, with highs in the low-to-mid 90s °F on Monday and Tuesday, before a significant cool-down midweek. Wednesday will see highs near 89 with an increasing chance of rain at around 40%, followed by a sharp drop Thursday and Friday into the mid-to-upper 50s with rain chances of 70 to 75%.

Looking back, the warm temperatures last Saturday were ideal conditions for thinning chemical applications, and many growers took advantage of that window. Given the heat early this week following those sprays, the effects of thinning should become visible by mid-week or by the end of the week at the latest. Fruitlets from the primary set in Adams County are greater than 20-25mm, depending on the variety. Any remaining crop load adjustment will likely be accomplished through hand thinning in the coming weeks.

Phenology in Central Pennsylvania

Even in blocks with very little primary set (Figure 1), the secondary and lateral bloom did not compensate as hoped. Fruit set from these secondary flowers remained poor (Table 1), and the hot weather experienced over the past week accelerated fruitlet drop from these positions. As smaller, weaker fruitlets from lateral buds are inherently less competitive and more vulnerable to abscission under heat stress, an early drop in this case is a favorable outcome, resolving crop load uncertainty sooner rather than later.

If additional thinning of secondary set fruitlets is desired, next week provides an opportunity to make those adjustments, as secondary fruitlets will be approaching 12 to 15 mm and can be readily removed at that size.

Managing Honeycrisp with a Low Crop Load

For Honeycrisp, especially on rootstocks such as G.11 or G.41, a low crop load increases the risk of bitter pit. When carbohydrate and nutrient competition is reduced, excess calcium is preferentially partitioned to vegetative growth rather than to fruit, further compounding this risk.

Given the low fruit set this season, return bloom NAA sprays, typically applied to encourage cropping in the following year, are likely unnecessary, as a light crop load itself promotes strong return bloom by reducing the carbohydrate and hormonal competition that drives biennial bearing. However, NAA should not be abandoned entirely, as early-season applications remain highly valuable for improving vascular connectivity within the fruit and reducing bitter pit risk.

Because calcium is transported exclusively via the xylem, maintaining xylem integrity through the critical cell division window is essential. Xylem within Honeycrisp fruit begins to rupture and lose functionality as early as 30 days after full bloom, and once broken down, those vascular connections cannot be repaired.

Griffith and Einhorn (2023) demonstrated that successive applications of auxins, including NAA, at 30, 45, and 60 days after full bloom significantly prolonged xylem function and vascular integrity, markedly reducing bitter pit incidence by approximately 65% in 2021 and 40% in 2022 by sustaining the vascular connections necessary for continued calcium delivery through the season.

On the irrigation side, with fruit set actively occurring in mid-May, maintaining consistent soil moisture is critical. Honeycrisp is particularly sensitive to water stress during cell division, and any deficit at this stage can compromise final fruit size and exacerbate calcium-related disorders by further limiting xylem-mediated transport. Irrigation should be run proactively on hot days (above 85 to 90°F) to prevent even transient water stress. Beginning in June, however, the strategy should shift: restrict irrigation to maintenance only, as over-irrigating promotes excessive shoot growth and dilutes calcium concentration in the fruit.

In Pennsylvania, many blocks will have reached 30 days after full bloom this week, making this the time to apply the first NAA spray at 2 to 3 oz per acre. The second and third applications should follow at two-week intervals thereafter.

Reference Information

References

Griffith, C., & Einhorn, T.C. (2023). The effect of plant growth regulators on xylem differentiation, water and nutrient transport, and bitter pit susceptibility of apple. Scientia Horticulturae, 310.

Growing Degree Day Accumulation

Current growing degree days for Adams, Berks, and Centre counties are provided in Table 2.

Acknowledgements

The Penn State Extension Tree Fruit Team wishes to thank our gracious collaborators who provided access to their orchards and fruit to sacrifice. These include:

• Adams County: The Penn State Fruit Research and Extension Center
• Berks County: Rick and Ben Keim, Keim Orchard, Boyertown
• Centre County: Penn State Russell E. Larson Agricultural Research Center
• Northumberland County: Bobby and Sara Hricko, Green’s Fruit Farm

Without their assistance, these reports would not have been possible.