Assessing apple bud damage following an advective freeze
Last week, a series of frost/freeze events caused flower bud mortality across multiple apple production regions in the southeast. Some sites observed up to 6 nights of subfreezing temperatures in a span of 8 days. The bulk of this system was considered as an advective freeze, as a large cold air mass passed through the area and brought high winds.
Frost control strategies (wind machines and overhead irrigation) were not an option during the majority of this event. Wind machines would only mix cold air with more cold air, due to the lack of an inversion layer. Excessive wind speeds (> 5 mph) could result in poor coverage of overhead irrigation systems. Insufficient coverage can promote evaporative cooling of plant tissues and subsequent cold injury. This is not the desired effect. Low temperature data is presented below from select weather stations in the region (Table 1).
To complicate matters, cold nights were preceded by an extended period of warm temperatures in late February / early March. From February 28th to March 16th, high temperatures exceeded 70° F on10 days of 17 days (Mills River, NC). During this same interval, 15 of 17 days exceeded 60° F.
The 26-year average growing degree-day (GDD; Base 50° F) accumulation for March 21 is ~77 GDD in Mills River, NC. As of March 21, 2026, 164 GDD were accumulated. This represents the highest level of GDD accumulation recorded on this date in at least the past 26 years in Mills River, NC (Figure 1; data and figure courtesy of the NC State Climate Office).
Figure1. Growing degree accumulation (base 50) in Mills River, NC is 164 GDD as of March 21st. This is the highest level of GDD accumulation on this date in the past 26+ years. Data and figure courtesy of the NC State Climate Office.
These unseasonably warm temperatures resulted in rapid changes in bud phenology and plant hardiness. For example, Gala went from side green to tight cluster in a ~10-day period. We captured a snapshot of bud phenology across several commercially relevant cultivars on March 14th (Mills River, NC; Figure 2). Growers at lower elevation sites reported that several cultivars were at pink bud stage and some early flowering cultivars had some open bloom at the timing of the event. High elevation sites had delayed bud development relative to lower elevation sites, but observed colder temperatures.
Figure 2. Range of bud phenology of several apple cultivars in Mills River, NC on March 14th, 2026.
We evaluated apple flower bud survival of multiple commercially relevant cultivars at the Mountain Horticultural Crops Research and Extension Center in Mills River, NC. The severity of frost/freeze damage was evaluated using a method for assessing fruit bud survival that was developed by Dr. Jim Schupp (Professor Emeritus, Penn State University). I am grateful for the help and dedication of my excellent team (Chris Clavet, Hannah Lepsch, and Tatiana Zuber). Over 2,900 buds were dissected and evaluated for this update.
Bud mortality ranged from 17 to 63% in the cultivars evaluated. While data from Mills River is generally positive and suggests potential for a full crop, reports from growers and extension professionals across the region have been mixed. While some feel that they still have potential for a full crop, I have heard reports of some locations/cultivars that have observed significant and serious injury. Several factors determine the potential severity of blossom mortality, including: site, location, bud development stage at time of freeze event, lowest temperature observed, the duration of low temperature exposure, cultivar, cropping history, tree health, etc. Given the numerous factors that could influence risk of cold damage in a given block, it is advisable to assess flower bud mortality at your own farm.
