Observationson Winter Injury To 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 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,,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 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 were: To observe differences in fined to the border lands of a fruitapple and pear tree varietal suscepti- zone but in one way or another makesbility to injury due to low winter tem- itselffeltwellwithintheregionsperatures; and to study the practical adapted to fruit growing. It is not avalue of using the more hardy varieties single matter of uniform, predictableas trunk and framework interstocks reaction to a given temperature but isfor the less hardy commercial sorts. modified, intensified, and palliated byHilborn, et al. (6) reported, "The use varying factors and is itself probablyof hardy trunkformers has long been a group of fatal or damaging reactionsadvocated both in the United States assembled for convenience or for wantand in Europe." For example, they of discriminating classifications understated further that Waugh, working in thesingle name of winter killing."Vermont in 1897, reported that tender

5 varietiesofapplesshouldbetop-order to avoid monotonous repetition. worked on a hardier sort. Each is used to indicate injury to fruit Other factors studied were differ-trees by low winter temperatures. Hood River Valley is a pioneer or- ences in character and extent of freez- ing damage to pear trees propagatedchard area located east of the Cascade on French (Pyrus coinmunis) or Jap-range in north-central Oregon. It is bounded on the north by the Columbia anese(Pyrusserotina)rootstocks. Studies were also made on extensiveRiver at an elevation of 100 feet and freezing damage from early winterfor 40 miles on the south by Mt. Hood pruning of Anjou pear trees and the (elevation 11,225 feet). The topogra- practicalvalueofwhitewashing orphy isessentially aseriesof three using board shields for protection ofbenches of about 500, 1,000, and 1,600 tree trunks. feet elevations, each merging gradually with theother. Orchard sitesvary The terms "winter kill," "freezingfrom flat areas to slightly rolling to damage," and "winterinjury,"aremoderately steep. Exposures to sun- used interchangeably in this bulletin inlight also vary widely.

CHARACTER OFFREEZE DAMAGE Gourley and Howlett (4) reportedwhen dead,drybark was subject on how freezing kills: "There is, even toadditionalcracking andsluffing. yet,no completeagreement among those best qualified to judge as to how freezing kills. It must be understood that a tissue my be frozen and re- cover, a rather frequent occurrence, or it may be frozen to death. Such tissues present a brown, water-soaked appear- ance shortly after they thaw and evap- oration is much more rapid than from living tissue." Damage to fruit trees by critically low temperatures in the hood River section generally includes bark lifting, perpendicular cracking, and permanent separation from the sapwood, and this isthe type of injury rcferred to in this publication unless otherwise indi- cated. This injury, often called "win- ter sun scald" is confined to the trunk and lower framework. It occurs mostly on south or southwest exposures where stresses are induced by rapid warming by sunshine on frozentrunks and branches. The full extent of damage, Typical low winter temperatureiniurytothe although severe, was often notap- lower framework of a Newtown apple treein parent until late spring or midsummer, the Hood River Valley.

6 Overley and Overholsei- (10) reportedthe sapwood. Early detection of this that in the state of Washington split-form of injury was possible only by ting of the bark of tree trunks was aclose inspection and incision. With this common form of winter injuryintype of injury, the dead bark very 1935-1936. of ten adhered closely to sapwood for Another form of killing was charac-long periods; sometimes for more than terized by close adherence of bark toa year.

WINTER WEATHER IN HOOD RIVER COUNTY Hood River County is subjected todreth, et al.(7) found that length of a wide range of winter temperatures.exposure to low temperatures has a The area is influenced to a great ex-marked effect upon the amount and se- tent by the prevailing temperate cli-verity of the injury, the killing being mate of western Oregon, butisoc- more or less in direct proportion to the casionallysubjectedtoextremesofduration of the freezing. During the usually short duration from the east.50 years, 78 days of zero weather or Within a 50-year (1912-1962) period,colder occurred in the lower valley and subzero weather occurred during 18142 days in the upper valley. Because winters in the lower valley (elevationof the topography of the area with its 500 feet) and during 28 winters in thehills and valleys, a noticeable tempera- upper valley(elevation1,600 feet).ture range usually occurs at times of (See Tables 1 and 2.) Prior to thislow recordings. As a result of this sit- time, zero temperatures or lower oc-uationexposure(i.e.,north,south, curred during 6 years in the 20-yeareast, or west) as related to winter sun- period, 1890-1909. Usually during coldshine, air, and soil drainagethe trees weather, lower temperatures are re-in any two orchards were not subjected corded at higher elevations. This con-to exactly the same conditions. There- dition, however, does not always pre-fore, damage was often variable. Or- vail. During the 50-year period, thechards on pronounced south or south- temperature was lower than _200 F.west slopes which were exposed to three times in the lower valley andwidely fluctuating temperatures during four times in the upper valley. Theperiods of extreme cold at night fol- lowesttemperaturerecorded duringlowed by warm sunshine during the thepriorperiod,1889-1910,wasday were most injured. Differences in 10° F. in 1893. The greatest differ- temperatures are reflected in the oc- ence that prevails in the two sectionscurrence of more extensive tree dam- of the Hood River district is the num-age in upper valley orchards than in ber and duration of cold periods. Hil- lower valley orchards.

CRITICAL WINTERS Subzero winter temperatures occurredtrees (Tables 1 and 2). During this 10- during eight years from 1919-1930.year period, destruction of trees was They are classed as "critical" becausegreater than in any other similar length of their continuity, intensity, and cum-of time. In the upper Parkdale Valley ulative overall killing effect upon fruitarea there were 60 total days of sub-

7 Table 1.Periodicity of sub-zero temperatures, Hood River, Oregon, 1915-1916 to 1962-1963' Days Mini- Snowfall below mum Dec., Jan., Years zero temp. Feb. Dates and minimum temperatures No. °F. In. 1915-16 2 -7 117.8 Jan. 17, -5° ;19, -7° 1919-20 6 -27 34.5 Dec. 11, -10° ;12, -25° ;13, -27° ;14, -23° ;15, -9° 16, 0° 1921-22 2 -12 47.5 Jan. 18, -12°; 19, -9° 1922-23 3 -2 80.5 Dec. 12, -2° ; 16, -1° ;17, -1° 1923-24 3 -4 11.8 Jan. 1-4° ; 2, -3° ; 6, 0° 1924-25 9 -12 9.5 Dec. 17, 0° ;18, -6° ;19, -3° ; 21, -5° ; 22, -10° ; 23, -9° 24, -11° ; 25, -12'; 26, -12° 1926-27 3 -11 32.4 Dec. 14, -5° ; Jan. 21, -10° ; 22, -11° 1928-29 7 -11 44.3 Feb. 7, -10° ;8, -11° ;9, -11° ;10, -10°11, -4° 12, -3° ;13, 0° 1929-30 10 -20 33.0 Jan.11,0° ;12, -1° ;13, -2° ;17, -2° ;20, -16° 21, -20° ; 22, -14°; 23, 0°; 25, 0° ; 28, 0° 1932-33 3 -2 44.1 Dec. 10,-i'; 11-2°; Feb. 9, -2° 1935-36 3 -4 32.7 Feb. 14, 0°; 16, 0°; 17, -4° 1936-37 5 -5 56.2 Jan. 7, 0°;8,-5°; 12,-i'; 30,0°;31,-4° 1942-43 1 -5 80.2 Jan. 18, -5° 1948-49 3 -5 68.7 Jan. 10, -2°; 24, -.5°; 25, _3° 1949-50 8 -21 103.0 Jan. 17, -5° ; 29, -5°; 30, -1°; 31, -17°; Feb. 1, -5°; 2, -17°; 3, -21°; 4, -1° 1955-56 2 -2 41.0 Nov. 15, -2° ; Feb. 1,-i'; 2, -2° 1956-57 6 -18 36.6 Jan. 26, -18°; 27, -15°; 28, -12° ;29, -12° ;30, -4° 31, 0° 1961-62 2 -2 14.2 Jan. 21, -2°; 22, -2° of above zero te,nperature are not included. Data are from the U. S. Weather Bureau Coop- erat,ve Station located at the Mid-Columbia Experiment Station, Hood River, Oregon. zero weather with one minimum ofof the country that trees which fruit -22° F. and an average of -14.3° F.heaviest are most likely to be injured In the lower Hood River Valley areaby low temperatures during the winter there were 43 days of subzero weatherimmediately following." McCoun (9), with one minimum of -27° F. and anwho made similarobservations,de- average of -12.3° F. During four win-scribed a row of apple trees ters, minimum temperatures were re-(21 years old) at Ottawa that behaved corded in December in both areas. Thein this way. Of 14 trees, 8 which bore incidence of severe freezes inearlya medium crop in 1917 were killed or winter and the fact that the leadingbadly injured, while 6 bearing either a apple varieties, Newtown and Spitzen-light crop or none at all came through burg, were in heavy production werethe winter in good condition. factorscontributingtowinterkill. The cold winter of 1929-1930 com- Gourley and Howlett (4)stated "Itpleted the 1O-year period of extreme has been observed in various sectionslow temperatures. Following this cycle,

8 Table 2.Periodicity of sub-zero temperatures, Parkdale, Oregon, 1915-1916 to 1962-1963° Days Mini- Snowfall below mum Dcc., Jan., Years zero temp. Feb. Dates and minimum temperatures

No. ° F. J 1915-16 3 -4 181.0 Jan. 12, -1°; 17, -4° ; 27, -1° 1916-17 1 -3 88.5 Jan. 31, -3° 1919-20 7 -22 69.0 Dec. 10, -5°11, -14° ;12, -21° ;13, -22° ;14, -17° 15, -12° ;16, 0° 1921-22 5 -10 53.1 Jan. 18, -9°; 19, _100; 31, -6° ; Feb. 28, -1° ; Mar. 1, -1° 1922-23 6 -15 109.0 Dec. 12, -15° ;13, -15°; 14, _120 ;15, _40; Jan. 30, 0° Feb. 15, -4° 1923-24 3 -9 30.8 Jan. 1, -9° ; 5, -1° ; 6, _20 23, _40 1924-25 8 -8 31.0 Dec. 17, -40;18, -7° ;19, -7° ;22, -3° ; 24, -8°; 25,60 ; 26, -3° 1926-27 4 -16 89.1 Dec. 14, -7° ; 21, -16° ; 22, -16° ; 23, -5° 1928-29 10 -15 122.0 Jan. 20, -3° ;Feb. 6, -8°; 7, -12° ;8, -15° ;9, -15; 10, -14°11, -8° ; Feb. 12, -5° ;13, ; 14, -2° 1929-30 17 -20 74.0 Jan. 10, -1°; 11, -7°; 12, -2°; 13, -5°; 14, -2°; 16, -2°; 17, -4° ;18, 1° ; 19, _40 ; 20, -12° ; 21, -20° ; 22, -17° 23, -1° ; 24, -1° ; 25, -2° ; 27, -1° ; 28, _20 1931-32 1 -1 109.8 Feb. 3, -1° 1932-33 8 -12 104.5 Dcc. 10, -6°; 11, -1°; 12, -6°; 15, -1°; 18, -1°; Feb. 9, -12°; 10, -7°; 13, -12° 1934-35 2 -5 71.5 Jan. 20, -5° 21, 0° 1935-36 4 -11 77.0 Feb. 8, -6° ;15, -8° ; 16, -11° ;17, -10° 1936-37 8 -14 140.0 Jan. 6, -1°; 7, -10° ; 8, -14° ; 12, -6°; 20, -7°; 21, -7°; 31, -5°; Feb. 1, -6° 1941-42 3 -5 42.0 Jan. 1, -1°; 2, -3°; 6,-5° 1942-43 3 -16 141.3 Jan. 18, -16°; 19, 00; 24, -3° 1946-47 1 -1 32.0 Jan. 15, _10 1948-49 9 -9 161.3 Jan. 9, -5°; 10, -9°; 11, _90; 12, -6°; 13, -7°; 23, -3°; 24, -8° ; 25, -9° ; 26, -2° 1949-50 15 -27 199.3 Jan. 3, -1° ;14, -5° ;16, 0° ;17, -13° ;18, -2° ; 25, -3° 26, -4°; 28, -10°; 29, -11° ; 30, -10° ; 31, -23° Feb. 1, -11°; 2, -17°; 3, -27°; 4, -5° 1950-51 1 -2 79.0 Jan. 30, -2° 1953-54 1 -12 93.3 Jan. 20, -12° 1955-56 5 -12 98.6 Nov. 15, -6° ; Feb. 1, -12° ; 2, -7° ; 3, 0°; 4, 0°; 16, -5° 1956-57 10 -23 100.8 Jan. 16, -5° ;17, -10° ;18, -5°;19, -6° ;25, -11° 26, -23° ;27, -20°; 28, -21° ; 29, -16° ;30, -11° 1958-59 2 -7 60.5 Jan. 2, -6°; 3, -7° 1959-60 1 -1 43.5 Jan. 14, -1° 1961-62 3 -7 51.2 Jan. 21, -6° ;7, -7°; 8, -3° 1962-63 1 -4 M Jan. 12, -4° Winters of above zero temperatures are not included. Data are from the U. S. Weather Bureau Coop- erative Station located at Parkdale, Oregon.

9 a continuous period of 20 years elapsedety was usually more severely injured when overall winter temperatures ofti-ian Delicious trees of the same age. the district were much less severe andThis low temperature occurred while periods of sub-zero exposure muchsome Newtown orchards werestill shorter. being harvested.Trees which were Although exact figures are not avail-bearing fruit and those which had been able, the 11,000 acres of apples in thepicked just prior to the freeze were in- Hood River district as of 1910 werejurecl more severely than those which reduced by the beginning of each sub- hadbeenharvestedapproximately sequent10-year periodasfollows:three weeks prior to the freeze. In ad- 10,750, 6,500, 5,400, and 4,500 acres.dition to trunk damage to many young The fall freeze of November 1955trees, a large amount of spur and bud is probably foremost in the minds ofdamage wasevidentthefollowing fruit growers inthe Northwest. Aspring. Damage to fruit trees by low minimum temperature of 2° F. in thetemperatures during the month of No- lower Hood River Valley caused se- vere tree damage to many young Deli-vember are caused largely by incom- cious and Newtown orchards whichplete dormancy. A temperature condi- were in the 5- to 20-year age group.tion such as this occurred only once Injury to trees in this group variedbefore 1955 in the Hood River dis- from complete girdling to slight barktrict, when a temperature of 6° F. lifting or splitting. The Newtown van-was recorded in November 1896.

APPLES Winter Damage Survey Followingthedisastrousfreezesapples,thegreatestemphasis was from 1919 through 1925, an extensiveplaced upon inspections of these two orchard survey was made during thevarieties. There were 6,781 Newtown summer of 1926 in all representativetrees examined and 4,837 Spitzenburg apple sections of the Valley to de-trees. Although fewer trees of other termine the character and extent of in-varieties were inspected, the averages jury and varietal differences in hardi-are considered to be an accurate cross ness. More than16,000appletreesection of the physical condition of the trunks and crotches of 11 yarieties indistrict. The nonhardy character of 219 orchards were critically examined. Newtown is indicated in that 78% of Data are summarized in Table 3. the trees showed injury in variable de- Injury classified during this surveygree, with 18% dead or removed. With and throughout other inspections wasSpitzenburg the proportions were 86% as follows: slight, where injury did notand 24%, respectively. The data also exceed 15% of trunk or trunk and indicatethe nonhardy characterof crotch area; medium, not exceedingJonathan, Winter Banana, and Ortley, 30% of the area;severe, exceedingwhile , Delicious, and Ar- 30% with no complete girdling; andkansas Black were more hardy. Black killed. Twig and Astrachan were remarkably Because of the commercial impor-free from injury and it was concluded tance of Newtown and Spitzenburgthat these two varieties were worthy

10 Table 3.Effect of low winter temperatures occurring from 1919 to 19261 on bear- ing apple trees at Hood River, Oregon2 Injury on trunk and lower framework Variety OrchardsTrees Slight Medium Severe Killed3 Total No. No. % % Newtown 65 6,871 14.2 11.5 35.7 18.4 78.9 Spitzenburg 51 4,837 13.6 12.1 36.1 24.1 86.1 Ortley 13 700 12.5 9.4 43.8 17.3 83.2 Delicious 12 616 20.6 8.4 18.0 5.0 52.2 Jonathan 11 652 16.1 9.2 44.9 17.4 82.6 Winter Banana 8 421 19.2 11.1 44.9 12.1 87.4 6 233 26.2 12.9 23.2 10.7 73.0 31 1,093 27.8 15.4 15.1 8.2 66.5 Black Twig 15 430 3.7 2.8 2.5 .0 9.1 Astrachan 4 45 8.9 2.2 .0 .0 11.2 Ben Davis 3 76 17.1 7.9 5.3 2.6 32.9 See Tables 1 and 2 for character of prevailing weather. 2 Survey conducted in summer of 1926. Throughout this report the termkilled' means trees so badly damaged that they were no longer com- mercially fruitful. of further study for use as intermedi- yearperiod.Observationsindicate, atetrunkstocks.Because oflimited however, that varieties of bearing age plantings, data are lacking on the har-which were rated nonhardy were also diness of young apple trees during thenonhardy at earlier ages. 1919 freeze and the subsequent 10-

Intermediate Trunkstock Studies Because of the very favorable recordseedling roots was planted for use as of Black Twig, one-year-old nurseryintermediatetrunkstocksforNew- stock of this variety on standard seed- town, Spitzenburg or Ortley, to which ling roots was plantedina10-acrethey were top-budded in about equal block at the Experiment Station in theproportion and in the same manner as lower valley in 1926. The trees weredescribed for Black Twig. There were set in the centers of 30 foot by 30 foot1,448 trees, 304 of which were planted squares as interplants in a 35-year-oldin about equal proportion in 18 cooper- Mewtown andSpitzenburgorchardative tracts and the remainder at the characterized by many replants andStation. The purpose of the project winter injured trees. This was knownwastodeterminetheirvigorand as the Black Twig block. The treesstructure, also their resistance toin- were top-budded during their secondjury from cold winter weather and year in about equal proportion to New-adaptabilityasintermediatetrunk- town,Spitzenburg,Delicious,andstocks. Trees of Astrachan, including Ortley. many apple varieties grown in mid- In 1928, one-year-old nursery stockwestern and eastern United States and of 62 other apple varieties on standardalso in eastern Canada, were included.

11 A uniform block of Newtowns topworked on Black Twig intermediate stocks. Strong, uniform, cion- stock unions are shown.

Our judgment of the factors influ-Hood River, although none of the win- encing the value ofthe intermediateters to which it was exposed were con- trunkstocks planted in 1926 or 1928 assidereci sufficiently severe to afford an shown in Table 4 came about throughexacting test. Rawlings, et al. (12) re- gradual accumulation of informationported "unusual and severe winter in- extending through 1952. Emphasis isjury to trunks of McIntosh apple trees placed on the need for vigor, sturdyin New Hampshire." Since the investi- framework, good unions of stock andgation was continued longer than was cion, and freedom from winter injuryoriginally anticipated, many trees were totrunkandframework.Withoutremovedbecauseofovercrowding. these valuable characteristics, an inter-With nearly all the varieties some rep- stock cannot qualify for favorable con-resentative trees were left in the plant- sideration. Most of those tested wereing, although their records were unfa- not satisfactory, and with many of thevorable. Most of the varieties showed varietiestheir undesirable charactersone or more weaknesses and were were apparent during the first 10 years.eliminated. Those favorably rated are The crab varieties used were unsat-indicated in Table 4 by an asterisk, isfactory because of incompatibility ofand those considered worthy of fur- cion and stock. Pronounced overgrowththertrial are indicated by a double at points of union with stock createdasterisk. weak branches with Hyslop, Trans- Further performance of the varieties cendent,andVirginiacrabs.Withselected from the previous study are heavy cropping, limb breakage was ex-shown in Table 5. These topworked cessive.McIntosh,consideredverytrees were all grown at the Experi- hardy in many eastern apple sections,ment Station in adjacent areas com- did not prove to be uniformly so atparable in exposure and growing con-

12 Severe limb breakage at incompatible unions of Newtown topworkecl on Transcendsnt Crab.

ditions.Black Twig trees,alsotop- worked, were in greatest number and were two years older, as previously noted, than those of the other varieties shown. Newtown was unworked and served as a check. Trees in this plant- ing were subjected to only two critical freezes at an early age. There were 6 days in February1929with 11° F., and 10 days in January1930with 20°F. The subsequentfiveannual freezes through January1949were comparatively mild, of short duration, and in mid-winter when the trees were completely dormant. Although temper- atures of 17° F. and21°F. were re- corded in January-February1950,the trees, then in their twenty-second year, were remarkablyfreeoftrunk or crotch damage. The deep snow cover- ing that year afforded good protection. Apple trees of intermediate to older ages throughout the valley showed very Overgrowth of Newtown donsatbud-unions little damage. with Hyslop Crab.

13 Table 4.Factors influencing the value of intermediate rootstocks

Performance of topworked trees

Varieties Frame- Winter injury Trunk stock worked1 Vigor3 work Cion unions (Range)

Alexander N-U MIoH Good Tjniiorm None 10 severe Anisette N L Poor Slight overgrowth None Anisim N-S-O MtoH Good Uniform None 10 severe Anlonovka N-S-U MtoH Good Slight overgrowlh3 None to severe Astrachan* N-S-U H Good Uniform None to stight Attison N-S-U M Good Uniform None to medium Baxter N M Good Uniform None to medium Black Twig* N-S-U H Good Uniform None to severe3 Ben Davis N M Fair Uniform None to medium Blushed Calvitle N M Fair Unilorm None Canada N-S-O MtoH Good Uniform None 10 severe Charlamofi N M Fair Overgrowth None to severe Coriland N-U H Good Overgrowth5 None to slight Duchess N-S-U H to H Fair Slight overgrowth3 None 10 severe Dudley N-S-U MtoH Good Overgrowth3 None 10 severe Erickson N-U MLoH Fair Uniform None to severe Fall St. Lawrence N-S MfoH Good Uniform None 10 severe Fameuse N-S-O M Fair Slight overgrowth None to severe Folwell N-S MtoH Fair Uniform None to severe Gideon N-S M Poor Overgrowth6 None to severe Gold Medal" N-S-U H Good Uniform None to slight Goodhue N-S-U M Poor Overgrowth None io severe Haas N-S-U MIoH Fair Slight overgrowth3 None 10 severe N-S-U H Good Overgrowth3 None to medium Herschel Cox N-S-U H Good Uniform None to severe Hibernat** N-S-U H Good Uniform None to severe Hyslop Crab N-S-U MIoH Good Large overgrowth None Lady N M Fair Uniform None to severe Liveland N-S MtoH Good Uniform None to medium Longlield N-S M Good Unilorm None 10 severl Malinda N M Good Uniform None to stighi Mann N-S M Fair Uniform None to severe McIntosh N-S H Good Uniform None 10 severe McMahon N-U M Poor Large overgrowth None to severe Milwaukee * * N-O H Good Unilorm Slight to medium Minnehaha N-S-U M Poor Uniform Slight to severe Minnesota 308** N-S-U H Good Uniform None 10 severe Minnesota 447** N-S-U H Good Unitorm None N-S-U M Fair Uniform None Northwest Greening N-S-U M Good Uniform Slight 10 severe Okabena** N-S M Good Uniform None to slight

14 Table 4.Factors influencing the value of intermediate rootstocks (Continued)

Performance of topworked trees Varieties Frame- Winter inj ury Trunk stock worked' Vigor2 work Cion unions (Range) Ostrakoff N-S-O H to H Good Slight overgrowth3 None Paradise Sweet #1 N-S-O H Fair Uniform None to severe Fatten Greening N-S M to H Fair Slight overgrowth None to severe Peerless N M Poor Slighi overgrowlh None to severe Red Siberian N-S-O Tel Fair Slight overgrowth' Slight to medium Red Wing N-S-O H Good Uniform Slight to severe Salome N-S-O lvi Fair Uniform Slight 10 severe Scott Winter** N-S-O H Good ['nilorm None Shields Crab N-S-O lvi to H Fair Slight overgrowth None Sierra Beauly N-S-O .11 to H Good Large overgrowth None to severe Soutard Crab N-S-O L Poor Large overgrowth None Stone N H to H Good Uniform None 10 severe Success Crab N-S-O H Poor Large overgrowth None to severe Sweet Orange #1 N-S-O H to H Good Uniform None to severe Telotaky N H Fair Uniform None 10 severe Tolman N-S-O MtoH Good Uniform None to severe Tolman x 804 M.A N-S-O Silo H Good Unilorm None to severe Transcendent N-O M Good Large overgrowth None Tikraine* N lvi Fair Slight overgrowth None Vermont No. 1 N-U Rio H Good Uniform None to severe Virginia Crab N-S-O H to L Poor Large overgrowth None to severe Wallace Howard N-S-O H Good Uniform None to severe Whitney Crab N-S-U M to H Fair Slight overgrowth3 None to severe \Vinter Banana - H Good None 10 slight Winier Rose N lvi Fair Uniform None to slight

Astrachan and Black Twig arc recommended for commercial use. Vareties recommended for further investigation. Variel,e.s worked: N; Newtown; S Spitr.msburg; 0, Ortley. 2 Vigor: H, high vigor; H, medium vigor; L, low vigor. Overgrowth with Newtown only. Treeswere planted in the orchard in 1928 (except Black Twig, 1926) and topsvorked by budding in the second grosving season. TIse Black Tsvigtrees weresubjected to 5' F. and F. in file svinter of 1926- 1927 (Dec. and Jan.)to which the othertrees werenot exposed; 9.2% of 249 treeswereinjured, 4.8% seve rely. Slight overgrosvth with Newtown. Extensive overgiosvth has been observed with Delicious. 'Large overgrowth with Newtossn; slight with Spitzenburg. Slight overgrosvtli with Ortley.

Thirty unworked Newtown trees oferable injury. Astrachan showed minor an original planting of 37 were in-injury only, as was also true of Gold jured during their first 10 years in the Medal, Minnesota 308 and Minnesota orchard (Table 5).Surprisingly, 12447. All were vigorous growers with Black Twig trees in the 1926 plantingstrong branches and framework. The showedseveretrunkdamage;the data, although based on a limited num- planting did, however, develop into aber of trees and severe test winters, in- Fine commercial, very heavy producingdicate that even the more hardy varie- block. Hibernal, rated very hardy inties may be injured at an early age. eastern fruit sections, showed consid-

15 Table 5.Performance of varieties selected for commercial use as intermediate - rootstocksr (from Table 7) Winter injury occurring on trunk and lower framework Trees Me- Se- In- Trunk intest5Slightdium vere jured Periods of zero weather 1928 to 1937 No. No. No. No. No. Days F. Newtownu 37 16 7 7 30i 1928-29 6 Feb. -1 l Astrachan 45 1 0 0 1 1929-30 11 Jan.-20 Black Twig 249 6 5 12 23i Gold Medal 17 1 0 0 1 1932-33 2 Dec.-2 Hibernal 35 5 3 1 9 1 Feb.-2 Minnesota 308 13 1 0 0 1 Minnesota 447 8 0 0 0 0 1935-36 3 Feb.-4 Scott Winter 5 0 0 0 0 1938 to 1947 No. No. No. No. No. Days ° F.

Newtown 34 1 0 0 1 Astrachan 43 0 0 0 0 1936.-37 5 Jan. -5 Black Twig 243 0 0 0 0 Gold Medal 17 0 0 0 0 Hibernal 26 0 0 0 0 1942-43 1 Jan. -5 Minnesota 308 13 1 0 0 1 Minnesota 447 8 0 0 0 0 Scott Winter 5 0 0 0 0 1948 to 1952 No. No. No.\o. No. Days F.

Newtown 29 0 1 1 2 Astrachan 23 0 0 0 0 1948-49 3 Jan. -5 Black Twig 243 0 1 0 1 Gold Medal 9 0 0 0 0 Hibernal 22 0 1) 0 0 1949.-SO 4 Jan.-17 Minnesota 308 8 0 0 1 1 4 Feb. -21 Minnesota 447 4 0 0 0 0 Scott Winter 5 0 0 0 0 Trees lopworked in 1928 to Newtovn, Spitzenburg, and Ortley; Black Twig Iwo years earlier. Decrease in original number of trees, mostly because of required orchard thinning program. Trees 25 years old in 1952. Uriworked Newtown considered as control for observations. Plantings con fined to the lower Hood River Valleyfor the most part at the Station. Trees injured niore than once during this period were given the maximum injury rating only. Minimum temperature recorded for each period. 0 Black Twig was planted in 1926 and exposed to -- U F. in J)eceniber and11 F. in January in the win- ter of 1926.1927. Other varieties riot subjected to these temperatures.

16 Some Practical Experiences with Topworked Astrachan The performance of Astrachan aseven more severetestin February an intermediate stock was observed in1950 when temperatures ofseveral many orchards during a long period.days duration reached a low of 27° F. Experiences in one of these, an upper Because of the low commercial rat- valley orchard located at an elevation ofing of Ortley, the variety was removed 1,600 feet, are of interest. Several hun-during the spring of the previous year dred Ortley trees were planted in 1932,by severe surgery below pointsof spaced 28 feet on the square. At theunion with Astrachan and grafted to same time, the tract was interplantedStarking Delicious inthe large,ex- with Astrachan, which were topworkedposed wood stumps. As a result of this to Ortley by budding in 1933. The areaexposure, growth from many Starking was exposed to an unseasonably lowcions was injured or killed. Although freezein1935 when temperaturessurgery of this character predisposes ranged from 10° F.to 30° F. Octo- trees to winter killing, injury to As- ber 30 to November 3. The trees weretrachan was minor. Inspection in 1952 then only semi-dormant and infull involving 151trees showed the fol- foliage. Unworked Ortley trees werelowing conditionoftrunks and severely injured, principally by partialcrotches :uninjured,85.6% ;slight, or complete girdling due to bark lifting10.5%; medium, 2.6% ;and severe, and exposure of sapwood. Further in- 1.3%. jury occurred during thefollowing Grower experience with Astrachan winter. Inspections in the summer ofas an intermediate trunkstock has been 1936 showed only 18% uninjured andgenerally favorable. Observations indi- 34% killedina247-treeplanting.cate that trees of this character are Trees of intermediate damage were in- vigorous,productive,andgenerally juredin varying degrees, many se- free of winter damage. We have, how- verely, while none of the 228 Astra- ever, noted some trunk damage in one chan trees topworked to Ortley wereupper valley orchard where heavily killed. Only five trees were injuredbearing Starking Delicious trees of in- slightlyinthe trunks and crotches.termediate age were topworked on As- Sonic damage occurred to Ortley topstrachan. Early winter pruning prior to but ended abruptly atthepoint ofsubsequent sub-zero temperaturesis union (Table 6). The Astrachan treesbelieved to be a primary predisposing inthis orchard were exposed to an cause.

Table 6.Performance of Ortley apple trees topworked on Astrachan as compared to the variehy growing on their own trunks1 T'egree and percentage of trunk and crotch injury Block No. of Trunk- no. trees stock None Slight Medium Severe Killed

1 247 Ortley tin- 18.0 10.0 26.0 11.0 34.0 worked 2 228 Astracitan 97.8 2.2 .0 .0 .0 Damaging temperatures ranged between + 10to +3 October 30 to November 3, 1935, when the trees were four years old.

17 Newtown appk variety topworked on an Astrachan intermediate trunkstock. Note the strong, smooth unions between cion and stock.

Fruit Production of Varieties on Promising Intermediate Trunkstocks Yield records based on loose apple Production averages as shown arc boxes were taken at the Experimentbelieved to be about equal to or better Station beginning at early bearing age.than those of unworked trees of similar The large, vigorous, topworiced blockage and growing conditions. A violent of the 1926 interplanted Black Twighailstorm in June 1947 caused severe trees startedlight production intheinjury to new growth and foliage. The seventh growing season. Annual yieldstrees were reduced in vitality for sev- for each of the 10-year periods 1932-eral years thereafter. Average annual .1941 and 1942-1951 were taken. Theyields per tree for the six subsequent annual tree average yields in boxes foryears decreased from the 19-20 bien- the first and second periods, togethernial year average as follows: New- with the 20-year overall average are astown 20%, Spitzenburg 26%, and Red follows: Newtown, 8.3, 156, and 11.9;Delicious 20%. This block oftrees Spitzenburg,10.9,14.3,and12.6; subsequentlyregained normal vigor StarkingDelicious,12.6,19.0,andand heavy production and now is re- 15.8; and Striped Delicious 10.1, 15.9,markably free of winter injury. and13.0. Records of Ortley are lim- Productionrecordsofthe1928 ited because the trees were reworkedplantingofsixintermediatestocks to Starking Delicious. The eight-yeartopworked to Newtown in comparison annualaveragepertree was11.7 to unworked Newtowns are shown in boxes. Table 7. Yields are rather unimpres-

18 Table 7.Average annual Newtown yields from trees grown on selected intermedi- ate trunkstocks as compared with unworked trees' Loose apple boxeshienniums at ages: Avg. acre Trunkstock 7-8yt-s. 10-11 yrs.13-14 yrs.16-17 yrs.19-20 yrs. 22-23 yrs. yield 1934-35 1937-38 1940-41 1943-44 1946-47 1949-50 1949-50

Astrachan 2 6 7 8 5 12 888 Gold Medal 1 3 4 10 8 9 666 Hibernal 0 4 6 8 7 10 740 Minnesota 447 0 4 8 9 7 10 740 Minnesota 308 0 3 8 13 7 .... Scott's Winter 1 5 7 10 6 11 814 Newtown (unworked) 1 6 7 10 9 12 888 Orchard double planted until the tStl, year. Average acre production during the last biennium t951-1952 Record lost. The average production for the 24-25 biennium was 14 boxes or 1,036 boxes per acre. sive, except when converted to an acretrees were also injured by the 1947 basis. In the spring of 1946, the treeshailstorm previously mentioned. The were spaced for the first time to 26 feetdata, although taken from a limited by 26 feet on the hexagonal, providingnumber of trees, indicate that with the 74 trees per acre. Prior to that time,interstock varieties shown, topworked there were 148 trees per acre, includingtreeshaveapproximately thesame interplants.Following theinterplantbearing capacity with Newtown as with removal, the remaining trees becameunworked trees. more vigorous and productive. These

PEARS Winter Damage Survey During the summer of 1926, fieldand Flemish Beauty. Cornice perform- inspections of pears similar to thoseance was outstanding. Total damage previously recorded for apples wereto trees of this variety was Only 4.4% made. The objective was to determineas compared to total damage to Anjou varietal differences in winter damageamounting to 60.3%; Bartlett, 50%; from the several severe preceding win-and Bosc 43.5% (Table 8). The rec- ters. Varieties shown in Table 8 wereords of both Easter and Flemish were 18 to 25 years old when inspected; ingood, but these varieties occurred in Table 9, 8 to 17 years; and in Tablefewer orchards and did not have as 10, 3 to 7 years. Because of more lim- good distribution as Cornice. In the in- ited plantings, fewer trees were avail-termediate age group, Cornice also ap- able for inspection than was true ofpeared in a favorable position. Only apples. 8.9% injury was recorded for this va- Total damage to Anjou,Bartlett, riety as compared to 47.7% injury for Bosc, and Winter Nelis pears wasAnjou, 42.7% for Bartlett, and 38% much greater than to Cornice, Easter,for Bosc (Table 9). Trees three to

19 Table 8.Effects of low winter temperatures on bearing pear trees (18 to 25 years old) from 1919 to 1925 (1926 survey)

Injury on trunk and lower framework Variety Orchards Trees Slight Medium Severe Killed Total No. No. % % Anjou 11 703 18.7 13.5 22.6 5.5 60.3 Bartlett 8 353 15.6 12.4 17.5 4.5 50.0 Bosc' 1 23 4.3 21.7 13.1 4.3 43.5 Cornice 25 402 3.0 1.2 1.0 .2 4.4 Easter 23 211 3.8 3.3 1.4 8.5 Flemish 10 94 8.5 5.3 1.1 4.9 Winter Nelis 14 315 15.5 15.5 10.8 1.8 43.6

Prior to 1919, the number of Bosc trees of bearing age in the Hood River Valley was extremely limited.

Table 9.Effects of low winter temperatures on pear trees of intermediate age (8 to 17 years old) from 1919 to 1925 (1926 survey)

Injury on trunk andlower framework \ arieties Orchards Trees Slight Medium Severe Killed Total No. No. % Anjou 34 2,354 15.9 11.9 13.8 6.1 47.7 Bartlett 9 232 22.0 9.1 10.3 1.3 42.7 Bose 4 142 14.1 9.2 6.3 8.5 38.0 Cornice 21 224 4.4 .9 3.1 .4 8.9

Table 10.Effects of low winter temperature on young pear trees (3 to 7 years old) from 1920 to 1925 (1926 survey)

Injury on trunk and lower framework Variety Orchards Trees Slight Medium Severe Killed Total No. No, % % % % .Anj ou 15 1,206 6.8 6.9 11.0 32.4 57.1 Bartlett 10 520 5.4 8.1 20.8 33.2 67.5 Bosc 19 2,272 5.1 8.0 9.2 29.0 51.3

seven years old were not subjected toCornice trees of comparable age. These the 1919 freeze but were damageddata show that Anjou, Bartlett, and subsequently. Total injury was: Anjou,Bose trees are susceptible at all ages 57.1%;Barlett,67.5%; and Boseto a wide range of winter damage from 51.3%(Table 10). There were nolow temperatures.

20 Investigation of Intermediate Trunkstocks The severity and frequency of in-ditions suitable for an extreme long- jury to the important commercial pearrange test. Sub-zero December varieties Bartlett and Anjou were pri-weather, which is the most critical pe- mary reasons why investigations wereriod, occurred only twice at the Station undertaken by the Experiment Stationbetween 1926 and 1952. A temperature to determine what pear varieties areof -5° F. was recorded on December suitableasintermediatetrunkstocks. 14,1927, -2° F: on December11, This project in its main objectives and 1932, and -2° F. on November 15, procedures coincided with those of the1955. Thereafter, until the conclusion similar investigation with applesre- of the study, low temperatures devel- ported in preceding pages. This projectoped only in midwinter and late winter. was started in 1928 and included 41As aresult of these circumstances, varieties of pears. These consisted ofmeasurable damage was confinedto 1,633 one-year-old trees, 801 of whichthe early years of tree growth. were planted at the Experiment Sta- Data in Table 11 indicate the char- tion and the remainder in 30 commer- acter and extent of winter injury to cialorchardsdistributedthroughouttrunks and lower framework of four the entire valley. They were topworkedunworked commercial pearvarieties to Anjou, Bartlett, or Bosc when twoduring the 10 years following planting years old. The trees were propagatedat the Experiment Station in1928. in about equal proportion on JapaneseMost of the damage occurred during roots(Pyrus serotina)and Frenchdormant periods starting in December roots (Pyrus communis). The latter1928, 1929, and 1932. During these were of European origin commonly re- three winters, there was a total of 20 ferred to as "True French" hybrids ofsub-zero days (Table 1). Bosc showed P\rus coniniunis. the highest resistance to injury with Fortunately for the grower, but lessonly 3.2% classed as severe and Anjou so for investigations of winter hardi-least with 12.7% severe. The data con- ness offruittrees, dormant seasonfirm the fact, as shown by the 1926 temperatures that followed the plant-field surveys, that these varieties may ing of these trees did not provide con- be classed as only semi-hardy in this

Table 11.Comparative winter trunk damage to unworked standard year varieties during their first ten years in the orchard, 1928 to 19371

Injury on trunk and framework Variety Slight Medium Severe Killed Total' % % % % % Anjou 4.9 33.6 12.8 3,9 55.2 Bartlett 4.1 43.8 4,2 .0 54.1 Bosc 18.7 15.6 3.2 3.4 40.9 Easter 7.7 31.0 7.7 3.8 50.2

Weighted average -- 7.4 31.1 9.3 3.3 51.1

Trees propagated on French roots. Severe and killed, considered comrnerciad injury.

21 area. The trees in this planting that crotches, mostly on the south or south- survived made normal growth,butwest sides, which persisted for many those which were severely injured de-years. Many of the large open wounds veloped open wounds on trunks andshowed heart-rot infection.

Winter Injury to Pear Trees on French and Japanese Rootstocks The trees from which data in Tablerespectively. Total injury to trees on 12 were taken were planted at the Ex-French roots was 3 1.3% and on Jap- periment Station in 1928. The ninea- anese roots, 62.9%. Keiffer has a bad rieties shown were used as intermedi- record, with 93.5% of the trees injui-ed atetrunkstocksonwhichBartlett, and killed on the oriental roots and Anjou, and Bosc in about equal pro- 42.6% injurcd and killed on French portion were top-buddedin 1929. Inroots. Gourley and Howlett (4)re- one area the trees were growing onported that Bartlett and Anjou pears French roots and in the other on Jap- have been found particularly suscep- anese roots. Attentionisdirected to tible to sunscald, while Comice, Easter, the weighted average incidence of win-and Flemish Beauty are less suscepti- ter injury during the first 10 years inble. The Easter variety on the Station the orchard. in every category of in-planting had a better record than that jury, the average was greater for treesof young trees of this variety in some on Japanese roots than for those onof the colder areas of the Hood River French roots. Only 4.9% of the treesValley. German Sugar, Cornice, and on French roots were killed and 4.6%Orel 15 have favorablerecords -on severely injured. On Japanese roots,French roots, but they need further the proportions were 20.3 and 11.7%,testing. The data show that all of these

Table 12.Comparative winter trunk injury to pear varieties used as intermediate stocks, 1928 to 1937 Trees onFrenchrootstock Trees on Japanese rootstock Variety of - Injuryon trunkandframework Injury on trunk and framework intermediate trunkstockSlight Medium Severe KilledTotalSlight Medium Severe .illedTotal % % % % % % % % % % Comice 15.2 2.1 4.2 2.1 23.6 25.0 5.0 15.0 15.0 50.0 Easter 13.9 .0 .0 .0 13.9 9.3 15.6 9.3 3.1 37.3 Flemish 5.7 14.3 11.4 2.8 34.2 .0 20.0 .0 20.0 40.0 German Sugar 4.7 4.7 4.7 4.7 18.8 12.5 6.2 6.2 25.0 49.9 Keiffer 7.1 7.1 14.2 14.2 42.6 18.7 21.8 21.8 31.2 93.5 Lemon 8.7 43.4 4.3 8.7 65.1 12.0 24.0 16.0 24.0 76.0 Old Home 11.7 20.6 .0 5.8 38.1 17.6 11.7 17.6 23.5 70.4 Orel 15 11.5 .0 .0 7.7 19.2 20.0 26.7 .0 13.3 60.0 Vicar 8.3 16.6 6.2 6.2 37.3 16.6 10.0 13.3 26.6 66.5 Weighted average 10.2 11.6 4.6 4.9 31.3 15.2 15.7 11.7 20.3 62.9

22 interstock varieties were susceptible to The apparent differences in hardi- variable trunk and crotch injury inness of pears on French or Japanese their earlier years when exposed to lowroots were confirmed in part from ob- temperatures in early winter. Anjou,servations made previously,particu- Bartlett, and Bosc pears are compatiblelarly prior to and during the extensive with all of the intermediate trunkstockfield survey in 1926. It was observed varieties listed in Table 12, and theythat many of the newer commercial developed strong uniform unions whenplantings were growing on Japanese budded or grafted. Bartlett, on suchstock, and that some nurseries were vigorous stocks as Vicar and Germanstill using these seedlings as founda- Sugar, made greater growth than thetion material. Such plantings, although same variety unworked. Growth of Un-vigorous and productive, were more worked Anjou, also a very vigoroussubject to winter trunk damage in un- variety, was greater than when top-favorably exposedareasthan were worked on Cornice, especially duringorchards on French stock. The discon- the first ten or more years. tinuance of Japanese stocks was rec- It was notable that only where one-ommended by the Station shortly after year-old,wellrooted,firstgrade1924. This proved to be very worth- Cornice trees were planted did the treeswhile advice. "Black End" and "hard prove to be satisfactory as intermedi-end" of pears was definitely associated ate stocks. with such stocks.

Trunkstocks Rated Unfavorably or Incompletely Evaluated Regardless of the fact that winterthis group ofvarieties was discon- temperatures were not frequent or ex-tinued. Many of these oriental species tremely severe following the planting werereportedasbeingextremely of the experimental trees, several vari- hardy in areas of their origin, includ- eties or species were found unsuited asing northern Manchuria, Korea, and intermediatetrunkstocks,principallyeastern Siberia. It is notable, however, because they as a group lacked winterthat although winter temperatures in hardiness. Injury varied from slight tothose areas are consistently and se- severeto killed during the first tenverely lower than those of the Pacific years on the Station or cooperativeNorthwest, climatic conditions are es- grower plantings. These stocks, propa-sentially different. The former are dis- gated principally on French roots, were tinguished by wet summers and dry planted mostly in 1928. With many of winters and the latter by dry summers the varieties there was repeated injuryand wet winters. The disappointing to the same trees dtiring several win- performance of these sorts may in ters within the period indicated. Thesemany respects be attributable to these were Bali Hsiang No. 1, Bali Seedlingconditions. No. 1, 2, and 3, Chieh Li, Chien Pa, Seventeen other varieties were tested Guar Li Seedling No. 2, Hung Guarastrunkstocksfor Anjou, Bartlett, Li Seedling No.1, Hung Guar Li,and Bosc. These were propagated on Huang Hsiang Sui, Hsiang Sui Li,both French and Japanese rootstocks, and Ma T. Huang. Further study ofand, except where otherwise noted,

23 were planted in 1928. Some have verythrough1943;theremainingtrees unfavorable records; others were too were severely damaged. limited in number or tested during too Certainotherintermediatetrunk- short a period to permit complete eval-stock varieties were tested but insuffi- uation of their respective merits. cient information is available for rec- Trees of the oriental species, Van- ommendations. These include Mendel, olosa, growing on French roots wereHansen, Warner, Douglas, Tait No. 1 planted in 1931 in an upper valley or-and 2, Farmingdale, Longworth, and chard. They were topworked to AnjouMinnesota No. 1, which showed vari when two years old and made splendidable injury during the first 10 years growth. The trees were uninjured untilfollowing planting. Small plantings of January 1942 when a temperature ofSerrulata were killed and Lincoln and 5° F. was recorded. Thirty-five trees, or 87% of the entire planting, wereBurkett were injured. killed. The trees,for the most part, Another trunkstockvarietytested were completely girdled by extensivewas Sicamous, a large tree of desir- bark splitting and separation from theable framework. The variety Patten sapwood, extendinginmany casesmay also have merit as an understock, from the ground to crotches. since itis rated as very hardy in the A planting of the Surprise varietyMidwest andnone ofthe 24 trees consisting of1,263 trees on Frenchplanted atthe Station were injured. roots was planted in this same upperHowever, the trees are only moderate valley orchard in 1919 and topworkedgrowers. Old Home, although very to Anjou, Bartlett, and Bosc. Exten-vigorous, is not considered meritorious sive damage occurred to trunks in Oc-as a hardy stock. Thirty-eight percent tober of the year they were planted,of the trees were injured during their when the temperature reached a low offirst 10 years in the Station orchard. 17° F. Twenty-four percent of theEarlier experience with this variety in trees were injured or killed by barkan upper valley orchard was unfa- lifting near the ground. During De-vorable. Forty trees were planted in cember 1919 with 20° F., and Janu-1923 and top-budded to Bartlett when ary 1922 with 10° F., extensive trunktwo years old. During four subsequent and framework injury occurred. More winters,sub-zerotemperatures oc- than 75% of the trees were removedcurred. Inspections made in midsum- in 1922. The remaining trees continuedmer 1927 showed 10% of the trees toexhibitnonhardycharacteristicsdead and 22% injured in variable de- during thefollowing10 years andgrees. By midsummer 1938, 12 addi- were removed. tional trees were dead with an equal Thirteen Estella trees growing onnumber showing injury,mostlyse- Ussuriensis roots were also planted invere. In 1943, only 19 trees, 47% of this orchard in 1923. Seven were killed the original stand, were alive.

Cornice as an Intermediate Trunkstock The very favorable record of Co-suits of subsequent experimental stud- niice resistance to winter damage as ies(Table 12) prompted further in- shown by the extensive field survey ofspections of three upper valley com- 1926 (Tables 8, 9, and 10) and as re-mercial tracts (Orchards 1, 2, and 3,

24 Table13)wherethisvariety was In a five-acre block planted in 1930 planted. A fourth planting of 105 trees (Table 13, Orchard 2), 100 represen- was made in Orchard 4 (Table 13).tative trees were inspected in the sum- Full-bearing Bartletttrees hadbeenmer of 1943 and again in 1949. Injury winter-killed and were gradually beingduring the 10-year period after plant- replaced by Cornice. The Cornice trees ing was inconsequential. The Bartlett in all of the four orchards were oncionswere vigorous and produced French seedling stock and topworkedheavily. This planting was inspected when two years old to Bartlett. again in 1951. The inspection included The trees in Orchard I were planted35 additional trees which were of sim- in a tract where winter tempeiaturesilar age and variety but not included in averaged somewhat lower than in otherpreviousinspections.Ofthethree areas of the upper valley. The plant-trees reported as dead, only one was ing consisted of 78 trees made in 1926.located in the original 100-tree tract. Air and soil drainage was poor. ThisAll of these are believed to have died was the same tract where Surpi-ise,froniexcessivepoorsoildrainage Old Home, Estella, and Variolosa va-rather than winter injury. The data rieties sustained excessive winter in-from Orchards 3 and 4 show that Co- jury as previously reported.Inthe rnice trunkstocks are remarkably ie- winter of 1927, eight trees were killedsistant to winter sunscald, bark split- by low temperatures. By 1934 two ad- ting, or bark lifting, any of which ditional trees were dead. Thereafter,alone orincombination cause sap- inspections in 1938 and 1943 showedwood exposure and induce attendant no further injury. This was the most decay. unfavorable record we have observed In contrast to the above results with for Cornice. Bartlett on Cornice understock,full-

Table 13.The extent of winter trunk damage to Bartlett pear topworked on Comice' as compared with standard stocks2

Trunk and framework injury Orchard Year Dates Trees 110. planted examined examinedSlightMediumSevere Dead Total No. No. AT0. No. No. No. 1927 78 17 7 0 8 32

1934 70 9 1 0 2 12 1' 1926 1938 68 0 0 0 0 0 1943 68 0 0 0 0 0 1943 100 12 0 0 0 12 2' 1930 1949 100 1 2 2 0 5

1951 135 1 1 1 3 6

1944 115 0 5 1 0 6 31 1927 1952 115 2 6 3 0 11 41 1937 1951 105 1 0 1 0 2

5-9 1925-1933 1944 580 93 101 106 83 383

Cornice. Standard stocks.

25 bearing standard Bartlett trees in fiveinjury in the following low propor- other upper valley orchards showed se-tions: slight injury, 8 trees; medium verecumulativedamage whenin- injury, 12 trees; severe injury, 2 trees. spected in 1944 (Orchards 5to9, None were killed. Table 13). All of the 580 trees in- During theperiod subsequent to spected were on French rootstocks.about 1950, a limited number of small The trees showed a total of 66.1%Cornice plantings were made through- trunk and crotch damage. out the Valley and topworked to Anjou The conclusions drawn from totalor Bartlett varieties. Some of these inspections made from 1926 to 1944plantings have made poor growth and are that the Barlettisat best onlyexhibit some trunk damage caused by semi-hardyinthe trunk and lowerlow temperatures. The exact causes framework. fortheseundesirablecharacteristics are not fully understood, but it is the There are still several old commer-authors' belief that the basic cause is a cial Cornice plantings in both the upperstock-cion incompatibility. It is highly and lower valleys where the trees wereprobable that these trees were propa- topworked at an early age to Anjou.gated on open-pollinated Bartlett seed- One is a 1927 planting in the upperlings. valley. Inspections were made in 1943 and again in 1951. During that period, only one tree showed slight trunk in- jury; three, medium injury; and one, severe. In a similar orchard in the same area, 81 trees were inspected in 1943 and 1952. The record indicates almost complete freedom from trunk injury. The first inspection showed nine trees with slight injury, and the last inspec- tion showed no additional injury. The largest remaining old planting of Cornice trees on French roots is a 20-acre tract located in the lower val- 1ev. The trees were planted in 1926 and top-budded the following year to Anjou. The tract is moderately rolling with a north to northwest slope. The trees made vigorous growth and at- tained large size. During the 25-year period following planting, the orchard was notably free of trunk damage, al- though adjacent unworked Anjou and Bartlett orchards of comparable age and growing conditions sustained much A close-up view of Anjou don topworked on injury. A final inspection made of 448 Cornice showing good unions of cion and stock trees in this orchard in 1950 showed and freedom from winter damage.

26 Relation of Time of Pruning to Severity of Winter Weather Heavy pruning prior to or duringthe understock was three years old severelycold,early winter weather (Table14).Intermittentsub-zero caused extensive damage or death toweather occurred throughout Januaiy. full-bearing Anjou and Bartlett pearEight days of this weather were re- trees in the Hood River area, particu-corded between January 6 and Febru- larly in 1948-1949 and 1949-1950 whenary 2. A minimum of 14° F. occurred prolonged and extremely low tempera-on January 8. Extensive injury was tures occurred. Several hundred acresobserved on thetrees shortlyafter were killed or so badly damaged as togrowth started in the spring of 1937, be reduced to a marginal status. Earlyfollowing a survey of pruned and un- pruning was prompted by the compar-pruned trees. Most of the injury was atively long period of mild wintersconfined to the trunk and lower frame- subsequent to 1933; also, by economicwork of the trees and was classified as reasons in the full utilization of thefollows:uninjured,14.6%;slight, orchardist's time and hired labor. Early10.9% ; medium, 17.1%; severe, winter pruning may be termed a calcu-54.8%; and killed, 2.4%. None of the lated risk when done with knowledgeunpruned adjacent trees which were of of the area's previous weather. Thosesimilar age and character and subject who guessed wrong paid a heavy tollto the same cultural management were asrecordedinthefollowing para-killed. Only two trees of the 102 in- graphs.Gourley and Howlett(4) specteclshowed severe damage and stated, "After the past two or three88.3% were uninjured. 'test' winters it has been observed that Another example of ill-advised early trees pruned just prior to the low tem-winter pruning applies to a block of 59 perature were more severely injuredtwelve-year-old Anjou pear trees, lo- than unpruned ones, and the heaviercated in a lower valley orchard, that the pruning, the greater the injury."were rather severely pruned in early The first example of severe winterJanuary1950. Theorchard was damage to Anjou pear trees dates backplanted on land sloping slightly to the to December 1936 when a block of 82east, and the air and soil drainage were ten-year-old trees was given a moder-considered fair to good. Two periods ate to severe pruning. The variety wasof sub-zero temperatures occurred fol- topworked by budding on Easter whenlowing the pruning. The temperature

Table 14.Effects of winter pruning prior to sub-zero temperatures of 1° F. to 14° F. in January-February 1936 on 10-year-old Anjou pear trees'

Injury on trunk and framework Plot no. Trees Treatment Slight Medium Severe' Dead Total

No. % % 82 Pruned 10.9 17.1 54.8 2.4 85.2 2 102 Unpruned 6.8 2.9 1.9 .0 11.7 Trees were pruned in early December 1936; they were inspected in the summer of 1937. Severe injury, considered commercial damage.

27 The effect of early winter pruning on 12-year-old Anjou pear trees. The trees on the right were heavily pruned prior to the low winter temperatures of 1949-1950, while those on the left were lightly pruned during the following spring. dropped to 5° F. on January 17, afterpruned trees were uninjured, only 2 which it remained above zero until ashowed severe injury, and none were second cold period of sub-zero weather killed. occurred beginning with January 29 A clear-cut demonstration ofthe and extending through February 4.risks involved in early winter pruning During this seven-day period, the tem-was observed in a 35-year-old Anjou perature ranged from zero to 21° F.orchard in an upper valley area fol- On two days during this period, read-lowing the winters of 1948-1949 and ings of 17° F. were recorded. It was1949-1950. This orchard was adjacent obvious from poor growth responsesto another Anjou planting, 25 years of during the following spring that theage, which was consistently pruned in trees were extensively and seriously[ate winter or early spring (Orchards 1 injured. By early summer, 1950, die-and 2, Table 16). Soil and air drain- back of the main limbs was generalage is excellent in both tracts. Each and was accompanied by prematureslopes to the east, a condition that fa- reddish discoloration ofthefoliage. vors a minimum of winter injury of Most of the adjacent unpruned treesthe sun-scald type. The only outstand- made normal, vigorous growth. As ing difference was that of time and se- shown in Table 15, only one tree in 59verityof pruning. Orchard 1 was of these early pruned trees was unin-pruned severely during several winters jured, while 49 were so badly damagedprior to and including 1949 and 1950, they were removed. In contrast, 31 un-whereas the trees in Orchard 2 were

28 Table 15.Effects of winter pruning prior to sub-zero temperatures of -17° F. to -21° F. in January-February 1950 on 12-year-old Anjou pear trees Block Trees no. Treatment examined Injury on trunk and framework Slight Medium Severe Dead Total No. % Pruned in 59 .0 3.5 11.8 83.0° 98.3 December 2 Unpruned 31 22.5 16.1 6.4 .0 45.1 Effects recorded in the fall of 1950. 2 Dead or removed as a resuit of very serious damage. Severe injury, considered commercial damage.

Table 16.Effects of winter pruning prior to sub-zero temperatures in the winters of 1948-1949 and 1949-1950 on mature Anjou pear trees1 Injury on trunk and framework Age Orchard of Block Time of Me- Se- no. trees no. pruningTrees Slight dium vere1 Dead Total2 Years No. % Prior to freezes 35 1 of 50 4.0 6.0 38.0 52.0 100.0 1949 and 1950 Prior to freeze 2 of 136 2.1 19.1 69.1 8.1 99.0 1949 After freezes 2 25 1 of 116 24.1 17.2 3.4 .0 44.8 1949 and 1950 'Temperature of -9° F. occurred in January of the winter of 1948-1949; -27° F. in January of the win- ter of 1949-1950. ° Data based upon inspection of orchard in September 1950. Severe injury, considered commercial damage. moderately pruned by light thinningment occurred a few days prior to and heading. A few large cuts weresub-zero weather of _10 F. on January made from time to time in the tops of3. During the following month, there the trees in order to keep height underwere 15 days when zero or colder was control. recorded with a minimum of -27° F. Effects of the pruning practices inon February 3. The cumulative dam- these two orchards were measured.age resulting from the 1948-1949 and The trees in Orchard 1, Block 1, were1949-1950 pruning was devastating in pruned in December 1948 and againcharacter. Evaluations made in the fall in December 1949. The latter treat-of 1950 indicated that 52% of the

29 trees were dead or subject to removalBlock 1 where the trees were pruned and 38% severely injured. No treesboth years in early winter. were found to be uninjured. In Or- In contrast to these conditions, the chard 1, the condition of the trees inperformance of the trees in Orchard 2 Block 2, adjacent to Block 1, whichis of interest. None of the trees were were pruned severely prior tosub-killed and only 3.4% were rated as se- zero weather in the winter of 1948-verely damaged. Where slight and me- 1949 but left unpruned until after colddium injury developed, the trees recov- weather of the 1949-1950 winter, wasered with no permanent impairment. likewise determined. The cumulative injury following these two winters, al- There were many other examples of though not as destructive as found insimilar experiences scattered through- Block 1, reduced the value of the treesout the Hood River Valley upon which to a marginal status. In this block, 8%specific information was not obtained. of the trees were classified as killedBased upon many observations, it can and 69% severely injured. We werebe stated that most of the severe win- unable to determine the extent of in-ter damage to pear trees resulting from juryattributabletothe1948-1949 theextremelylow temperaturesof freeze because inspections were madeJanuary and February in the winters only in1950.It appeared, however,of 1948-1949 and 1949-1950 was con- that extensive damage occurred duringfined to trees that were pruned prior the 1948-1949 freeze which was notto the occurrence of sub-zero weather apparentduringthe1949 growingin one or both of these years. The de- season. Many trees so injured in eachgree of damage was associated with the block made vigorous growth that year.severity of pruning. The trees which Repeat injury during the 1949-1950were pruned extensively and in early winter took a heavy toll, particularly inwinter suffered most.

Shading of Tree Trunks: An Effective Means of Reducing Winter Damage Whitewashing oftree trunks andfrom the trunk on the southwest. The use of board shields was found effec-shields were placed in the orchard in tive in reducing winter damage. TheNovember 1926 and the condition of purpose is to reduce rapid absorptionthe trunks was determined in late sum- of heat from bright sunshine in ex-mer of 1927. The following observa- posed orchard areas on days followingtions were made: extremely cold nights when tree tissue is frozen. Reference is made to results Damage of experiments of this character re- TreatmentSlight Medium Severe Total ported in Oregon Experiment Station Circular 103 (2). Board shields 3.3 .0 .0 3.3 Original tests were conducted in a No treat- 10-year-old Anjou orchard located on ment 21.4 7.1 57.1 85.6 a pronounced western slope.Board troughs, made from 1 foot by 12 foot The experiment was repeated in the material was placed about 6 incheswinter of1929-1930. Low tempera-

30 Board shields placed on the southwest side of Anjou pear trees provide an effective means of reducing winter damage. tures occurred in January. Fifty-two degrees F., the maximum temperature recorded, was followed by a minimum of 19.5° F. Zero or sub-zero temper- atures occurred at different times over a period of more than two weeks, dur- ing which time many of the days were clear and bright. Snow in the orchard varied in depth from 2 to 15 inches. The practical value of white tree paint and board shieldsindeflectingthe sun's rays was clearly shown. The per- centageoftreesshowing damage, which varied from slight outer bark injurytocomplete girdlingofthe trunks, was as follows: Unprotected trees,40.0%;withboardshields, 19.2% ;and with whitetreepaint, 10.0%. Practical experience indicatesthat orchards on northern slopes are less subject to seriously damaging winter trunk injury than plantings on south or southwest exposures. Following the Whitewashing of the lower areas of apple and pear trees is an effective means of reducing in- 1926 freeze, Newtown apple trees in jurycaused by wide extremes of low winter the Experiment Station orchard, pro- temperatures.

31 tected from the direct rays of the win-degree. On the other hand, 75% of the ter sun by timber and windbreaks,unprotectedtreessuffereddamage, showed only 18% injury of varyingmostly severe.

CONCLUSIONS AND PRACTICAL CONSIDERATIONS The primary concern of the averagedamaged at earlier ages appear to be apple and pear grower in the Hoodmoreresistanttoinjury,although River Valley is for the protection ofthere have been fewer severe expo- his treeshis capital investment. De-sures. The continued commercial use preciation, if gradual, may be absorbedof Astrachan and Black Twig (Arkan- in annual costs, but if abrupt and ex-sas) as intermediate stocks for New- cessivethe impactisoftensevere.town has been highly satisfactory. Sev- With many of the pioneer apple grow-eral other stocks have merit. ers, the savings and efforts of many The preservation of our principal years were greatlyreduced orde- pear varieties, Anjou and Bartlett, is stroyed by the low temperatures inalso a primary grower concern. They December1919and the seven othermay be classed as only semi-hardy in sub-zero winters to1930.The 40% ap-the Hood River Valley. Each was ex- proximate reductioninappletreestensively damaged during critical win- from about 10,750 acres in1920to ters. Several varieties appear to have 6,500 acres in1930was caused pri-merit as understocks, but further test- marily by winter injury in that decade. ing for their full value is needed. The Probably no fruit grower who has hadsplendid long-range merit which was experience with losses of this charac- established by Cornice as a hardy, mer- ter and is aware of the cyclical charac- itoriousunderstockisatpresent ter of the winter weather pattern inclouded because of uncertainty as to Hood River fails to appreciate the haz-the character of rootstocks now being ards involved. Hood River is not alone used. with experiences of this kind. Other Determination of the value of inter- northwest fruit districts have had lowmediate trunkstocks needs additional winter temperatures during the sameand revised study in relation to recent years as those in this area and severebasic changesinhorticulturalprac- losses also. tices. These include variety changes, Many of the apple varieties whichintroductionofdwarfing rootstocks, had prime commercial status when ourand modification of cultural practices. first observations were made have beenWinter hardiness problems, will, how- mostly eliminatedin new plantings. ever, remain. Among these are Spitzenburg, Ortley, Itis common knowledge that cul- Arkansas Black, and Winter Banana.tural practices greatly influence winter Newtown, however, will probably con-hardiness of fruit trees. Gourley and tinue to be one of our leading varieties. Howlett (4) indicated, "In a soil man- Our observations and experiments in-agement program which results in high dicate that this variety is subject to var-moisture and nitrates throughout the iable trunk and lower framework win-middle and latter part of the season, ter kill. Many of the older(30yearswinter injury to the above-ground por- and older)Newtowns which weretions might be more serious than in

32 other systems of culture." Overcrop-pruning should be delayed until the ping and reduced vitality from manydanger of sub-zero temperature has causes, such as failure of insect pestpassed. and disease control, may be predis- Topworking of fruit trees, especially posed factors to winter kill. On theduring their formative years is a pains- other hand over-irrigation and exces-taking and exacting job, and it should sive nitrogen fertilization may also bebe undertaken only by one familiar in error. We believe that the hazardswith the skills and principles involved. which are involved in early-winter se-The location, number, and placement vere pruning cannot be overstressed.of buds or grafts is a determining fac- Although all of the causes of plant in- tor on how young trees are to be jury by freezing are not fully known,trained. Many young trees are ruined for our purpose it is sufficient to sayat the start by unskilled and indifferent that pruning by exposing wet, woodywork. The transition in the tree from tissue reduces the insulating effect ofone variety (the understock) to an- the bark which covers and protects theother is channeled through a few buds most susceptible portion of the tree,and too often severe surgery predis- the cambium area. For the good of theposes the tree to late growth and possi- fruit trees, the welfare of the orchard- ble winter injury and also to temporary ist, and the fruit industry as a whole, dwarfing which delays bearing.

ACKNOWLEDGMENTS We are indebted to the following state ex- Agriculture; and many Hood River orchard- periniental stations for assistance in supply- ists who planted varieties under cooperative ing eithertrees or cion wood atvarious tests. times: Minnesota; Southern Oregon; Iowa; We also are indebted to Dr. Elmer Han- Illinois; Michigan; Wisconsin; also the Do- sen, Professor of Horticulture, Oregon State minion Experimental Farms, Horticultural University,for reviewingthismanuscript Branch, Ottawa, Canada; the Bureau of and offering suggestions relative to the pres- Plant Industry, United States Department ofentation of the subject matter.

LITERATURE CITED

Bradford, F. C., and H. A. Cardinell, Eighty Winters in Michigan Orchards. Mich. Sta. Bull. 149, 1926. Childs, Leroy, and Gordon G. Brown, A Study of Tree Stocks in Relation to Winter Injury and Its Prevention. Oreg. Sta. Cir. 103, 1931. Gardner, V. R., F. C. Bradford, and H. D. Hooker, The Fundamental of Fruit Produc- tion, 1939. Gourley, H. G., and F. S. Howlett, Modern Fruit Production. New York, The Macmillan Co., 1941. Havis, Leon, and J. P. Lewis, Winter Injury of Fruit Trees in Ohio. Ohio Agr. Expt. Sta. Bull. 596, 1938.

33 Hilborn, M. T., and J. H. Waring, "A Summary of Investigations on the Use of Hardy- Trunk Stocks in Maine." Proc. Am. Soc. Hoyt. Sci., VoL 48, 1946. Hildreth, Aubrey Clair, Determination of Hardiness tn Apple Varieties and Relation of Some Factors in Cold Resistance. Minn. Agr. Expt. Sta. Tech. Bull. 42. 1926. Levitt, f.Frost Killing and Hardiness of Plants: A Criticol Review. Burgess Pub. Co., 1948. McCoun, W. T., 'Winter Injury in Canada." Proc. Amer. Soc. Hart. Sci., 15: 13-17, 1919. Overley, F. L., and F. L. Overholser, "Low Temperature Injury of Fruit Trees in Cen- tral Washington during 1935 and 1936." Proc. H/ash. Hort. Assoc., 32 :147-152, 1936. Potter, G. F., Experiments on Resistance of Apple Roots To Law Temperatures. N. H. Agr. Expt. Sta. Tech. Bull. 27, 1924. Rawlings, C. D., and G. F. Potter, "Unusual and Severe Winter Injury to Trunks of McIntosh Apple Trees in New Hampshire." Proc. Amer. Soc. Hart. Sci., 34: 44 48, 1937. IT. S. Dept. of Agr. ARS. Special Rpt., Damage and Recovery n Deciduous Orchard Trees From Major Freeses, 1959, pp. 22-49.

34