On behalf of Chris Doll (University of Illinois Extension, retired)
Most fruit growers in the Midwest realize that the recent winters have been pretty favorable to their crops, and that the big crop loss in 2012 was from spring frosts.Â During my career, which dates back to 1941 when I remember picking Black Twig apples on November 11 just ahead of a blizzard and zero temps.Â I followed this by studying cold hardy stocks for apples at Kansas State U. a decade later, and being involved in fruit research on varietal hardiness and cold resistance for Iowa State U. for 14 years.Â At Council Bluffs, IA. I saw effects of -25 degrees F. on most of the common tree and small fruits, including early trials with the French hybrid grapes.Â Loss of vegetative growth was most common on hybrid grapes and red raspberries, (black raspberry in one year), while flower bud loss was common on peach, apricot and Asian plums.
That and years of observations since then have included many years of loss of tender flower buds in the mid-1970’s through the mid-1980’s, and a near duplication of the 1941 Armistice Day freeze in early December of 1990.Â The Illinois peach crop the following year was less than 10000Â bushels, with some tree kill also.Â Some loss of apples, primarily Jonagold, in northern Illinois has been seen after test winters since then.
It is known that resistance AND acclimation are two factors that affect freezing injury. To me, the classic resistance is that of labrusca grapes, and other hardy species, when compared with vinifera and some of its hybrids.Â For that reason, I have concerns about the Midwest grape and wine industry that has not seen the damaging minimum temperatures in recent years. And, for all of the new Prunus inter species and varieties that have been touted as cold hardy, this might be the test, and I hope that my pessimism is for naught. Acclimation has been discussed by specialists primarily on what might be expected based on pre- and post-freeze temperatures.Â It is why late season fertilization of peach trees is not advocated.Â The example ofÂ December pruning of apples ahead ofÂ a dynamic freeze has been mentioned, and observed by Mitch Lynd,(Ohio), myself and others.Â Site and soil selection also can play an important part or prevention too.
After all of the above, I hope that this is just another of theÂ worrisome cold spells that growers must go through, and that the remainder of the 2013-14 winter if less stressful.Â Chris
Dr. Elizabeth Wahle, Ph.D.
Extension Educator, ANR (Horticulture)
University of Illinois Extension