Written by Greg Peck, Assistant Professor of Horticulture, Cornell University

Gee whiz, 2020, you really have it in for us! In the midst of a global pandemic in mid-May apple growers throughout the Midwest and Eastern US endured several nights of potentially damaging cold temperatures. At our research farms in Ithaca and Lansing, NY we had below freezing temperatures on May 6, 7, 9, 13, and 14 (Figure 1).

Figure 1. Hourly temperatures in Ithaca and Lansing, NY from May 5 to 15, 2020.

However, it’s important to note that because of the solute concentration in the flower bud cells, and the protective layers around the buds, the absolute cold temperatures typically need to be several degrees below freezing to cause damage (Figure 2). You will also notice that as the flowers develop from silver tip to petal fall, they become more susceptible to freeze damage.

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Figure 2. Critical temperatures to cause 10% and 90% damage to apple flowers from silver tip to fruit set. (Image from: Utah State University Extension and Utah Plant Pest Diagnostic Laboratory using data originally published by Washington State University: https://s3.wp.wsu.edu/uploads/sites/2086/2014/05/budctap.jpg)

The amount of damage that occurs is also very much so dependent upon the air movement, humidity, number of hours below the critical temperature, tree health, soil moisture, moisture on the bud surface, and if any frost control methods were used, such as wind machines, helicopters, overhead irrigation, or heat. A thorough discussion of frost control methods written by Michigan State University Extension Educator Amy Irish-Brown can be found at: https://www.canr.msu.edu/uploads/files/2013_NW_orchard_show/OrchardShow13Irish-Brown.pdf

Damage to the apple flowers can also vary. Typically, the king bloom (center flower in the cluster that usually becomes the largest apple at harvest) is several days more mature than the side blooms in the whorl. Thus, the king bloom is more likely to sustain damage. For culinary apple producers who sell wholesale, this can be a major problem since pricing is very much tied to fruit size. For cider producers, individual fruit size is less of an issue than tonnage per acre. Additionally, apples typically produce up to 95% more flowers than can reasonably be carried as fruit (not to mention that over-cropping leads to biennial bearing) some level of frost damage is tolerable. The threshold for how much damage is acceptable depends upon the initial flower bud load and yield expectations.

One other thing for the cider industry to remember is that many of the European cider cultivars tend to bloom later than culinary apple cultivars and crab apples. Local and regional apple industry reports tend to be more focused on culinary apples. So, how the freeze damage might affect your apple selling or purchasing this fall will depend upon the types of apples that are being used for cider.

So, how much damage occurred around the country this spring? I’ll give an update from New York and a few colleagues and growers in other regions have shared what they experienced, as well. (Note: I did some minor copy editing for clarity.)

Figure 3: Frozen water on the surface of the flower helps protect the flower from damage because a small amount of heat is generated as water freezes. (Credit: Greg Peck)

New York (May 27): In the Finger Lakes region of NY, despite temperatures down to 26 ºF in our research farm (23 ºF at my house!) we probably only sustained 10-15% damage to the earlier blooming cultivars and much less to our research cider apple trees. Several growers I’ve spoken with report similar findings. We’re now at late pink to full bloom for most of our apple cultivars with excellent pollination conditions. I suspect we’ll start out the season with the potential for a full crop. The Lake Ontario region of NY has had variable damage from none to greater than 80% of the flowers being damaged. Typically, growers who are closer to the Lake will have less frost damage because the cold water in the Lake delays flowering by several days or more. Reports from the Hudson River Valley are also variable, but more growers in that region appear to have sustained damage than those in the Finger Lakes or Lake Ontario region. Update (June 18): After surviving several frosts and a hail storm, the particularly warm temperatures during bloom have led to several cider apple growers in the Finger Lakes reporting that they have fire blight infections. For our conventionally managed research orchards, we applied streptomycin four times (we use predictive models to determine the need to use this antibiotic), but we were still not able to prevent infections. I think most of the infections were from a late afternoon shower on June 6. We had sprayed strep on June 4 after hail went through the Ithaca research orchard and with just a handful of flowers not open at that application, I thought we would be okay. Big mistake. Most of the infections started in flowers on one-year old wood, including on the central leader. We’re cutting out as much as we can, but I may need to rip out my Dabinett trees and start over. The Medaille d’Or and “Geneva” Tremlet’s Bitter trees also had a large number of fire blight strikes. There was a moderate amount of fire blight on Ellis Bitter, Harry Master’s Jersey, and Yarlington Mill. Porter’s Perfection only had a couple-few strikes, likely due to the fact that it blooms about a week earlier than the other English cider cultivars. Despite all of these issues, if we can stay ahead of the fireblight infections we should have a decent crop overall.

Renae Moran, University of Maine (May 14): “We are at the beginning of pink on Macs, and still at tight cluster for Honeycrisp.  I have not checked apple buds yet, but I don’t think it got colder than 30 ºF in most places. Peaches that survived the winter are mostly still alive, but most orchards had 50% or more bud death by April. Peaches are just starting to bloom. Sweet cherries in a frost pocket are dead. The ocean effect delays bloom in Maine, and most growers have orchards at high elevation which also delays bloom. Poor soils are the compromise for escaping frost in most years.” Update (June 16): “I have not checked statewide, but in southern Maine, we had freezing temperatures around June 1, at the petal fall stage. Obvious injury to fruitlets was reported by two growers in the Newport area. In my orchard, I am seeing heavy fruit drop which is probably due to this freeze, and some due to normal thinning. I am also seeing about 10% of the apples with frost rings. Other growers are reporting the heavy fruit drop, as well.”

Terry Bradshaw, University of Vermont, Burlington, VT (May 14): “We’re actually looking pretty good here on the freeze front, although I need to check on a few folks in the southern part of the state. I’m still at early pink on most stuff, tight cluster on some. On cider varieties, a bit of half-inch-green, even. Lows haven’t been that low: 31.8 ºF on May 9th in Shoreham, 28.4 ºF in Essex where buds are tighter than ours.”

Liz Garofalo, UMass Extension Fruit Program, Belchertown, MA (May 27): “There were a few sites in MA where we dipped (on May 10, at 3am one site hit 30.7 ºF, warmed and then dropped back down to 31.7 ºF from 5-6am) below freezing for an hour or two. But, with cider varieties being largely behind others in terms of bud development, they have escaped bloom damage, and the worst that we are seeing are some crinkly leaves from prolonged cool temperatures. Of course, we are now knee deep in fireblight weather with varieties like Stoke Red just barely at pink in one location. For reference, the pink date for that particular variety and location was May 19. All of our apples look like they are setting a good crop, weather has improved, and bees are buzzing.” Update (June 16): “Nearly 75% of Massachusetts is currently experiencing “abnormally dry” weather conditions. In Belchertown at the UMass Cold Spring Research Orchard, we are down 5.38 inches from the yearly average precipitation accumulation. Tree stress caused by water deficits increases the likelihood of opportunistic pathogens and insects that would not normally pose a problem in the orchard- things like black stem borer and phomopsis. High density plantings, especially new and newly established plantings, should be receiving regular irrigation to ensure healthy trees and a healthy crop. We are not yet seeing fireblight strikes. Given the late blooming nature of some of our cider varieties, however, there is still time for strikes to show up in MA.”

Megan Muehlbauer, Rutgers University, Pittstown, NJ (May 26): “New Jersey growers have seen vast differences in frost damage to culinary apples across the state this spring, with crop losses ranging from 0 to 100%.  In some instances, several feet of difference in elevation at single farms resulted in complete crop loss. At the Snyder Research Farm in Pittstown, NJ the lowest temperature recorded over the past 30 days was 31 °F.  Thus, it seems the late blooming hard cider apple varieties have been spared (a few of which were still in full bloom/petal fall) as of May 25.” Update (June 18): “As of mid-June the hard cider apple crop in New Jersey is looking beautiful.  It seems that they have all bloomed just late enough to avoid the most brutal of the spring frosts (Mid-April was particularly disastrous for many other crops).  The fruit set looks excellent, thus far there looks to be barely any damage.  I haven’t seen or heard of any particularly bad fire blight incidents either, although we have been vigilant with preventative sprays at both our research site and in discussion with growers.”

Figure 4: The flower on the top right is undamaged and still has the potential to become a fruit. The flower on the bottom left has damage to the pistil and ovaries, thus it will not become a fruit. (Credit: Greg Peck)

Diane Flynt, Foggy Ridge Cider, Dugspur, VA (May 13): “Spring was mostly kind here in Southwest VA—cool, with little frost damage in last weekend’s sub 28 ºF temperatures for two nights running. Wind was a big issue during bloom, with 18 to 20 mph wind most days (and nights) so spraying was a challenge. But it looks like we have decent fruit set and I hope for a good harvest. Last year I had 40 cidermakers ask to purchase our fruit, and was able to sell to only 4. All my current customers say they want to purchase again—I pass this along as a counter to anxiety growers may be facing about selling cider fruit this year. We are TINY but I do think this demand is an indication of continued interest in high quality cider apples. I hope we don’t see contraction in planting cider apples in response to the challenges cidermakers are facing in selling. Virginia Wine has done an outstanding job in communicating with the industry since isolation began in VA, and I think most of the cidermakers that were doing a decent job before the virus will come out OK.”

Tom Kon, North Carolina State University, Mills River, NC (May 26): “Southeastern apple growers (NC, SC, and GA) observed at least four frost/freeze events during spring of 2020. The polar vortex occurred when fruit was ~18 mm in diameter, but temperatures dropped slightly below freezing at most sites. While most growers avoided catastrophic losses, some blocks/sites are exhibiting sub-lethal cold injury (frost rings, russet, seed damage etc.).”

Nikki Rothwell, Michigan State University, Traverse City, MI (May 26): “We do have some damage in apples in Michigan. I think the areas in the south have more than us here in the north. It has also been pretty variety dependent. Red Delicious, which I know is not used for cider, has more damage than other varieties. However, we had great pollination weather, so I think many growers will have a decent crop. We just need to get through this fire blight weather. We are in bloom with Epiphytic Infection Potential (EIPs) in the 200-300!”

Chris Gottschalk, Michigan State University, East Lansing, MI (May 26): “On May 9th, mid-Michigan sustained temperatures of 25 ºF for two to three hours overnight. As a result, many of our early flowering cider cultivars in the Great Lakes Cider Apple Collection sustained freeze damage. Estimates ranged from 0% loss to >50% loss. For example, Chestnut crab (early blooming) was at first pink and lost >50% of its flowers to the cold. Whereas Cimitiere, a very late blooming cultivar, was at 1/2 inch green and did not suffer any damage. In general, most of our cultivars lost the king blossom but will still produce a sizable crop load this year.” Update (June 17): “The frost that Michigan experienced in early May has decreased crop load levels, for both cider and fresh market types. At the Great Lakes Cider Apple Collection, our Chestnut Crab (an early-blooming cultivar) was severely affected by the frost and has an extremely small crop load. In contrast, Vista Bella (another early-blooming cultivar) was unaffected by the frost and is supporting a high crop load. Our fresh-market industry is reporting similar results with crop load levels being very cultivar dependent. Our late-blooming cultivars, Dabinett and Cimitiere, both were unaffected by the frost and will produce a large crop this year. Many of our other accessions, that bloom at similar times to the fresh-market types, such as Sweet Alford, Yellow Newtown, Esopus Spitzenburg, Gravenstein, and Winesap all have light crop loads.”

Doug Hill, Deep Roots Orchard, Watervliet, MI (June 17): “Early bloom varieties in our orchard Redfield, Granniwinkle and Grimes Golden were negatively effected by the freeze in May. Temps dropped into the low 20’s (22-25) for several hours. Below freezing for 5-6 hours. I am happy to report that other varieties of later bloom were less affected.  Browns Apple, Cox Orange Pippin, Spitzenburg, Dabinet, Harrison, Kingston Black (spotty), porters perfection. I noticed some spotty dead blooms on some of the trees but overall we feel lucky about our outcome. Trees were planted in 2017.”

Katie Nash Suding, University of Colorado, Boulder, CO (June 16): “In the Front Range of Colorado we had a late April snow storm which damaged many flowers and so we are expecting generally low fruit set.”

Brant Clark, 63rd Street Farm Orchards, Boulder County, CO (June 18): “The late cold weather, which coincided with the bulk of blossom season, more or less wiped out production for this year. We have one tree with one apple, a Golder Russet on Antonovka rootstock. Our guess is that the tree is not well (leaves more yellow than green) and so bloomed late, thereby missing the freezing event.  Additionally, an earlier cold snap and major snow, measured 51cm/20″+, damaged the new leaves on early trees. Leaves which were below the snow survived with little or no damage, leaves above the snow were killed. Most of our trees are on mid and late season rootstock, so suffered little, if any, damage.”

Brady Jacobson, Mt. Hood Organic Farms, Hood River, OR (June 16): “I know the Midwest and East had severe cold weather that might have reduced the crop. We, on the other hand had great weather for bloom and set a big crop in Hood River, OR. Problem is it hailed a few nights ago, so we will have a lot more processing apples for sale this year.”

Carol Miles, Northwestern Washington Research and Extension Center, Mt. Vernon, WA (June 16): “Here in western WA we have not been negatively impacted by temperature. We have had a bit of rain though this past month, and this has led to slightly cooler temperatures, thus fruit development may be a little slow at this time in this region.”

Karen Lewis, Washington State University, Moses Lake, WA (June 17): “The apple crop looks fine in Eastern WA – we have a few pockets of frost damage but overall, if it all sticks and we manage our crop load, then we are on track. It has been a cool, wet and windy spring. Only a few warm days in May. Temperatures are on the way up this week and into next week ( 90’s). Somewhat steep increase but trees /fruit aren’t stressed.”

Jake Mann, Five Mile Orchards, Watsonville, CA (June 18): “We had two amazing seasons here in 2018 and 2019 with excellent growing conditions across the year: sufficient chilling hours and good rains, a gorgeous bloom with no frost or major precipitation during pollination, followed by a mellow summer growing season into harvest with enough folks around to pick the fruit when it was ready. 2020’s crop is looking promising, even considering this should be an alternate bearing year. Precipitation was lower this winter, but chilling hours were once again sufficient. Weather was clear and warm during bloom. Nice fruit set. Intermittent spring rains necessitated some scab control sprays, and we’ve seen outbreaks of aphis and skin worm (moths) in May and June, but have been able to keep them under control. If you wanted to say there was a pattern developing over the past three years, it’s that we’re seeing dryer winters, later accumulation of chilling, with more precipitation in spring rather than winter. The Newtown Pippin crop (our main cider apple here) looks solid, not as bountiful as last year for some blocks, but still feeling optimistic. It’s looking like a big year for our Red Delicious (not the most sought after cider fruit, true) and a worthwhile crop is growing in our other dessert fruit sections. The test blocks and grafts we have for Kingston Black, Wickson, Nehou, and some other cider-specific varieties show promise for adapting these in greater quantity to our region. The orchards didn’t get the memo about Covid… our small crew remained busy though the spring and have been able to work at a safe social distance from each other. We remain optimistic that our fruit will find it’s home in the markets this fall.”

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