Observationson Winter Injury To Apple and Pear Trees In the Hood River Valley Station Bulletin 595 November 1964 Agricultural Experiment StationOregon State University, Corvallis CONTENTS Page SUMMARY 3 INTRODUCTION 4 CHARACTER OF FREEZE DAMAGE 6 WINTER WEAThER IN HOOD RIVER COUNTY 7 CRITICAL WINTERS 7 APPLES 10 Winter Damage Survey 10 Intermediate Trunkstock Studies 11 Some Practical Experiences with Topworked Astrachan 17 Fruit Production of Varieties on Promising Intermediate Trunkstocks 18 PEARS 19 Winter Damage Survey 19 Investigation of Intermediate Trunkstocks 21 1vVinter Injury to Pear Trees on French and Japanese Rootstocks 22 Trunkstocks Rated Unfavorably or Incompletely Evaluated 23 Cornice as an Intermediate Trunkstock 24 Relation of Time of Pruning to Severity of Winter Weather 27 Shading of Tree Trunks: An Effective Means of Reducing Winter Damage 30 CONCLUSIONS AND PRACTICAL CONSIDERATIONS 32 ACKNOWLEDGMENTS 33 LITERATURE CITED 33 AUTHORS: GORDON G. BROWN was Horticulturist at the Mid- Columbia Experiment Station from 1916 to 1952; WALTER M. MEL- LENTHIN is horticulturist and Superintendent of the Mid-Columbia Station; and LERoY CHILDS was Superintendent froni 1914 to 1952. Observations on Winter Injury to Apple And Pear Trees in the Hood River Valley GORDON G. BROWN, WALTER M. MELLENTHIN, and LEROY CHILDS SUMMARY During the 50-year period whichmercial practicability of using nursery ended in 1963, sub-zero winter tem-stock of many apple varieties of known peraturesoccurredduring18 yearsor considered winter hardy character with 79 total days in lower Hood Riveras intermediate trunkstocks on which Valley at 500 feet elevation and dur- Newtown,Spitzenburg,andOrtley ing 28 years with 142 total days in thewere topworked when stocks were two upper valley at 1,600 feet elevation. years old.Sixty-four varieties were Greatest cumulative damage to appleemployed as intermediate trunkstocks. and pear trees was caused by sub-zeroProminent among these were Black temperaturesduringeightdifferentTwig and Astrachan. Although most winters from 1919 to 1930 in four otof those tested were unadapted, Black which extreme lows occurred in De- Twig and Astrachan proved to be very cember. Extensive field surveys weresatisfactoryasintermediatetrunk- conducted in the summer of 1926 to de- stocks. Others showing promise were termine the character and extent ofHibernal, Gold Medal, Minnesota 308, damage to apple and pear trees in rep- and 447. Many crab varieties, notably resentative commercial orchards in theHyslop and Transcendent, were una- district.From inspectionsofmoredapted because of incompatibility of than 16,000 apple trees of differentcion and stock. ages in 219 orchards it was found that Extensive experimental tests were Ortley,Jonathan,Spitzenburg,and also started in 1928 to determine the Newtown showed extensive injury orpracticabilityof using pear nursery death in trunks and ci-otches. Blackstock of known or considered winter Twig (Arkansas) and Astrachan va- hardy character as intermediate trunk- rieties were highly resistant and showedstocks for Bartlett or Anjou. Forty- only slight injury. one pear varieties were used. Those Frominspectionsof9,051peai considered worthy of additional study trees of different ages in 204 orchardsare Cornice, German Sugar, Orel 15, it was found that Bartlett, Anjou, andVicar, and Flemish. Bosc showed extensive injury or death Our most favorable impression of in trunks and crotches. Flemish BeautyCornice as an intermediate trunkstock and Easter varieties showed much lessfor Bartlett or Anjou comes from a injury.Corniceshowedonlyslightstudy of the performance of this vari- injury. ety in some of the older Anjou or Extensive experimentaltests wereBartlett orchards where many trees started by the Hood River Station ii came under our observation after sev- 1926 and 1928 to: determine the corn-eral severe winter frezes. Those trees 3 which are known to be propagated onceeded that on French roots (Pyrus seedlings or hybrids of Py'rus corn-communis) in a ratio of about 2 to 1. niunis of European origin are out- Anjou pear trees pruned in early standing in vigor and freedom fromwinter 1948 and 1949 prior toex- trunk or crotch injury. Younger or-tremely low temperatures werese- chards which appear to be growing onverelyinjured orkilled.Unpruned open pollinated Bartlett pear seedlingtrees showed only minor injury. rootshavenotmadesatisfactory Whitewashing of pear tree trunks growth nor have they been consistentlyand crotches was found effective in re- resistant to winter injury. ducing injury due to direct exposure to The weighted overall average inci- theafternoonsun'sraysfollowing dent of winter injury to nine pear va- lownighttemperatures duringthe rieties used as intermediate stocks onwinter. Board shields were also effec- Japanese roots (Pyrus serotina)ex- tive. INTRODUCTION Temperature, with its variables, con-sented stresses the significance of long- stitutes one of the dominant factorsrange weather patterns and indicates associated with successful commercialpractical means of reducing losses to a fruit production.Fruit varieties,in minimum. Conclusions are based upon order to survive and produce abundantextensivefieldsurveys and experi- crops of high quality, demand certainmental work conducted during a major limits insofar as extremes in tempera- portion of the period indicated. ture are concerned. Man in his attempt Although apple trees as a class ap- to expand or develop new producingpear to be more tolerant of cold than areas to a large extent has demon-pear trees, no rigid rule can be applied stratedtheselimitswithpresentlyat a given temperature. The extent of known varieties. At one end of thedamage depends to a large degree upon scale, low winter temperatures are thethe date of the freeze and the condi- limiting factors, and at the other thetion of the trees at the time of its oc- absence of sufficient cold weather tocurrence. Usually, the greatest damage prevent satisfactory production. follows early winter exposure and is Extremely low, prolonged, andrelated to lack of complete dormancy. widely fluctuating temperatures, espe-Trees of low vitality, induced by poor cially in early winter, are primary fac-culturalpractices,inadequateinsect torswhich causesevereinjuryorpest and disease control, or heavy crop- death to many apple and pear trees inping exhibit reduced resistance to crit- Hood River Valley. Table 1 on pageically low temperatures. Experience in 8 summarizes official minimum tem-the flood River Valley indicates that a perature records for December throughminimum of _300 F. is about the lower February each year from 1915 to 1963limit most commercial varieties of ap- and other tables present data showingples and pears will withstand with only the character and extent of damage.occasionalexposure.The United These studies record variety response States Department of Agriculture (13) to variable climatic conditions duringin summarizing limits of cold resist- criticalyears. The information pre-ance of deciduous orchard crops mdi- 4 cated that in midwinter when trees areThis definition of winter damage per- fully dormant, the minimum tempera-formance is applicable to the Hood tures that most varieties may be ex-River Valley. Levitt (8) reported that pected to tolerate in northern areas are"so called 'winter injury' takes a tre- about asfollows: Apples, _200tomendous toll of plant life in all but the 30° F. and pears, 10° to 15° F. Thetropical climates. Consequently, inves- degree of inherent winter hardiness oftigators have long looked for some a variety is very important and is themethod to combat it. It is evident that basis of much of the data and recom-by far the most destructive factor is mendations presented. the actual freezing of the plant." Havis, In a study of winter temperatureset al.(5) stated, "During the period and their effects in Michigan orchards1779 to 1936 (160 years) 19 test win- covering a period of 80 years, Brad-ters were recorded in northern United ford and Cardinell (1) found that aStates. These were exceedingly cold winters or what have been called 'test freezeoccurringinOctober1906 caused the greatest injury to fruit treeswinters'. The average was one such even though the temperatures werewinter in 9 years." above zero. A parallel experience was The problems of winter hardiness recorded in the Hood River area infor tree fruits are not ones which con- 1935 when apple and pear trees stillcern only fruit growers in Hood River in full foliage were exposed at an ele-Valley. They also apply to complex re- vation of 1,600 feet to temperatures oflationships and cultural practicesas 10° to 30° F. in late October and earlythey affect other fruit sections of the November. Severe trunk and crotchPacific Northwest. Serious losses else- damage, principally bark lifting,oc- where were caused by low winter tem- curredinseveralyoungorchards.peratures which often occurred during Gardner, Bradford, and I-looker (3) the same periods. Low \rjnter tempera- have well expressed the vagaries oftures which frequently occur in eastern winter temperatures in connection withfruit sections have caused extensive fruit growing by stating: "Damagedamage and death to trees and continue from freezing is not confined to anyto be a serious threat to the industry. one region; it is definitely as injurious in California and Florida for tender The primary objectives of our in- species as in Montana and Wisconsinvestigational studies in the Hood River for more hardy fruits. It is not con-Valley