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Volume 10 Oregon State University , May 1966 Number 1

Resistant Rootstocks Control Pear Root AphidEffect of Storage Temperature

On Ace Lily Bulbs TestedThe problem of flowering Easter lilies on time becomes

acute when Easter is as early as it will be next year,March 26. Poinsettias commonl y occupy the greenhousebenches until Christmas, making it difficult to pot andhandle the lily bulbs until after the benches have beencleared. Yet, if the bulbs are not potted and benched untilafter Christmas, a maximum of onl y 91 clays is availablefor forcing in 1967. Furthermore, with the major shiftby the industry from the relativel y fast-forcing Croft tothe relatively slow-forcing Ace, timing becomes even moreacute.

It is especiall y important with a very earl y Easterthat the bulbs be sufficiently precooled if they are to flowerin the shortest possible time without the greenhouse opera-tor having to resort to excessivel y high forcing tempera-tures which blast flower buds and lower plant quality.On the other hand, excessive precooling can drasticallyreduce the bud count, shorten the basal leaves, lengthenthe internodes, and reduce the leaf count. The leaf count,however, must be reduced because the days to flower aredirectly proportional to the leaf count.'

Avoid problemsMany west coast greenhoUse operators avoid the prob-

lems that follow precooling storage by potting the bulbsin the autumn and placing them outdoors in coldframesor other protected places where the y are subjected to thecool temperatures of autumn and early winter. The bulbs

' L. T. Blaney, D. E. Hartle y, and A. N. Roberts, Preheatingbefore precooling benefits Easter lil y bulbs. The Florists' Review,133 (3439) : 23-24, 70-71, October 24. 1963.

(Continued, page 2)

Pear root aphid (Eriosoma pyricola) is a serious pestof young pear trees, both in the nursery and the orchard.Nursery trees infested with this insect may be stunted tothe extent that they are unmarketable. Similar stunting orgeneral reduction in vigor can occur during the first fewseasons in the orchard, especially when the soil becomesdry in late summer.

Possible control of this insect b y using resistant root-stocks was indicated by work done in California about 50years ago. Oriental stocks were more resistant thanFrench (Pvrus communis). F. C. Reimer in Oregon re-ported that P. callervana, P. ussuriensis, and P. betulae-folia were highly resistant and that P. serotina was moder-ately resistant, while P. communis was susceptible.

The data in Table 1 were taken at digging time fromnursery trees propagated in 1965 to learn the general char-acteristics of a large number of rootstocks. Root aphidswere not placed on these roots, but observations weremade of natural infestations under field conditions.

Data agreeWhile the data generally agree with previous reports,

a number of new points are shown. P. communis typeswere variable but generally susceptible. The P. communisfrom Turkey were more resistant than others of the spe-cies and indicate a possible source of material for select-ing resistant stocks of P. communis.

Seedlings of pure P. callervana, P. bctulacfolia, and P.serotina had no aphids on them, while open-pollinatedseedlings of these species had some infestations. Knownhybrids generall y reflected the characteristics of the parentspecies. The one source of P. ussuriensis, obtained from acommercial nursery, showed 50% mild infestation, indicat-ing that these seedlings may not be pure P. ussuriensis.Reimer reported this species to be more resistant thanP. serotina.

(Continued, page 3)

Oregon Ornamental and Nursery Digest is published by theAgricultural Experiment Station, Oregon State University, Corval-lis, G. B. Wood, Director.

Material may he reprinted provided no endorsement of a com-mercial product is stated or implied. Please credit Ore gon StateUniversity . To simplif y technical terminology, trade names of prod-ucts or equipment sometimes will be used. No endorsement ofproducts named is intended, nor is criticism implied of productsnot mentioned.

Single copies of the Digest will be mailed free to Oregonresidents on request.

Comments and questions are welcome. Address correspondenceto the Department of I forticulture or to the author concerned.

Storage Temperature .. .Continued from paw 11

root down and the early stages of sprouting occur as thebulbs are naturall y precooled outdoors. Bulbs handled inthis wa y usuall y produce excellent plants that force rapidlywith satisfactory bud counts.

The effects of several storage temperature regimes forpreparing Ace bulbs for forcing were tested by the storagetreatments outlined in Table 1, page 4. Seven-inch bulbsgrown on the Pacific Bulb Growers' Research and Develop-ment Station, Harbor, Oregon, were used. The y were har-vested September 10 and stored in sealed polyethylenepoultry bags with 1 gram bale-dr y peat ( approximately50(4 moisture) per 5 grams of bulbs. A 6-week period at40° F. was included in each of the treatments as the pre-cooling temperature. It was preceded by storing the bulbstwo weeks at either 32° F. or at 70° F., because earlier ex-periments had shown that these temperatures lessened thedestructive action of 40° F. on the flowering potential ofthe bulbs. The bulbs were then held at 32° F. until potting.They were potted on November 19. December 8. and De-cember 27 in 6-inch cla y pots in a porous, unsterilized soilobtained from a well-rotted compost pile containing woodchip bedding front cattle barns. The coldframed bulbs,which had been held in a well-ventilated shed after harvest,were potted September 24 and benched in the greenhouseon November 24. A forcing temperature of 70° F. dayand 60° F. night was emplo yed throughout the forcingperiod. The plants were dilute fed when watered.

Results givenThe results of these storage treatments are shown in

Table 1. page 4. The onl y plants which flowered by March26 were those of treatments 1 and 2. Those of treatments 3and 4 could easil y have flowered by March 26 if the forcingtemperature had been raised, as is commonl y done in com-mercial greenhouses. Treatment 5 plants would have re-quired a much higher forcing temperature than the fore-

(Contnued, page -11

"Sour" Sawdust MulchMay Damage Ornamentals

For mulching and other horticultural uses, dark col-ored, more-or-less-rotted sawdust is often preferable tothe fresh product because of better appearance and some-what lesser nitrogen demand. In such large piles as arcfrequent with commercial storage, moist sawdust becomesso compacted deep in the piles that aeration is excluded andanaerobic fermentation results. End products, includingvolatile organic acids. accumulate in this absence of freeoxygen and excessive heating, often causing charring andeven spontaneous combustion. Even if not charred, a darkbrown sawdust resulting from the fermentation is stronglyacidic and has a pungent odor. I f used for mulching pur-poses it will kill man y plants. not onl y seedlings but shrubsand young trees. Some of the fumes are volatile acids andthese will cause at least a yellowing of leaves and defolia-tion even if below-ground parts are not injured. In somecases the plants eventuall y recover. This is generall y true oflawn grass; Severity of injury is dependent upon rate ofapplication and weather conditions. Leaching b y rain orirrigation accelerates root damage, while warm air tem-perature hastens evolution of fumes and results in rapidinjury to leaves and tender plants.

Sour sawdust should never be used for mulches, pottingmixes, or soil conditioners. The pungent. penetrating odorof any dark sawdust should provide sufficient warningagainst its use. To counteract the acidit y , whether the saw-dust is black or brown, requires from 250 to 300 pounds oflimestone per ton. On the other hand, fresh sawdust re-quires less than 10 pounds per ton: well-rotted sawdust,in which the rotting took place in the presence of air, mayrequire 50 to 70 pounds limestone to neutralize some acid-ity that develops even with more or less free oxygen.

—W. B. B OLLEN

K. C. Lt:Oregon Agricultural Experiment Station and

Forestr y Sciences Laboratory, U. S.Forest Service, Corvallis

Compacted sawdust pile with this dark central "sour" area may damageor kill ornamentals if used as a mulch.

7

Resistant Rootstocks .. .( Continued from page 1)

P. pashia, native to India, Pakistan, and Nepal, wasuniforml y susceptible to root aphid. It is an exception, inthat it is the onl y Asiatic species susceptible to aphid.

Two natives of Asia Minor, P. amvgdaliformis and P.elaeagrifolia, are highly resistant to root aphid and deservefurther study as possible rootstocks for domestic pears.

All types of quince tested also were resistant. Thisagrees with other reports that quince is generally resistantto pear aphid.

A few seedlings of two other pear stocks appeared tobe resistant to root aphid. One is the Korean wild pear, P.faurici, and the other is P. svriaca, a native of Israel. Little

is known of these species as rootstocks, and further workmust be done to determine their possible value.

It should be pointed out that two of the aphid-resistantstocks, P. ussuriensis and P. serotina, are highl y suscepti-ble to pear decline and should not be used as rootstocks.

Other more detailed studies on pear root aphid arebeing carried out at OSLT by the Department of Entomol-ogy. Dr. Knud Swenson is stud ying the life cycle of theinsect as it is affected by the environment. Dr. Peter Westi-gard at the Southern Oregon Experiment Station, Med-ford, is using root pieces of different pear species to studyroot resistance to aphid feeding under controlled condi-tions.

N. WEsTwoonH. 0. BJORNSTADHorticulture Department

Table 1. Infestation of several Pyrus rootstocks with pear root aphid (Corvallis research nursery, 1965)

Rootstock

Numberof

Root aphid infestation :

trees none mild moderate severe

P. communis:C

Medford Station sprouts 54 50 50 0 0Old Home x Farmingdale 100 58 33 0 9Domestic French 352 30 35 17 18Imported French (Europe) 205 44 38 12 6P. communis (Turkey) 31 80 20 0 0Special Hartnian seedlings 34 10 50 0 40

P. callervana:Source A—pure 30 100 0 0 0Source B—open pollinated 19 75 0 0Source C—open pollinated 12 67 33 0 0C. P. type—source unknown 11 73 27 0 0

P. betulacfolia:Medford Station—pure 40 100 0 0 0Medford Station—open pollinated 100 62 38 0 0Italy—open pollinated 138 33 67 0 0

Other species :P. ussuriensis (P. C.) 68 50 50 0 0P. pashia 48 0 50 50 0P. phacocarpa 4 50 50 0 0P. scrotina 4 100 0 0 0P. amvgdalitormis 178 100 0 0 0P. clacagrifolia 33 100 0 0 0Cydonia oblonga (quince) 48 100 0 0 0

H ybrids :P. betulacfolia x P. communis 35 17 66 17 0P. betulacfolia x P. callervana 18 67 33 0 0P. cancscens x P. betulacfolia 41 50 50 0 0P. CalleSCCIIS x P. communis 57 0 75 ? D 0P. canescens x P. callcrvana 55 50 50 0 0P. canescens x open pollinated 18 0 0 100 0P. callervana x P. communis 10 100 0 0 0P. longipcs—open pollinated ').? 33 67 0 0

3

Storage Temperature . .(Cont)tued from page 2)

Table 1. Effect of several storage treatments on forcing performance

•

of 7-inch Ace lily bulbs harvested Sep-tember 10, 1965 (averages based on 10 bulbs per treatment divided into two 5-bulb replications)

Treatment Storage Datenumber treatment potted

Bulbweight'

EmergenceFirst open

flowerBud

countPlant

height'Leafcount

Plant diameterabove pot

date days date days at 3" at 6"

weeks (°F.) + days (°F.) grunts inches inches1 Cold f rame' Sept. 24 88 Dec. 7 13 March 26 122 6.1 15 96 14 142 ' (32°) 6 (40°) Nov. IQ 87 Dec. 13 24 March 1 9 122 5.1 15 67 14 143 ? (70°) 6 (40°) Nov. 19 86 I )ec. 18 29 April 3 134 5.5 16 94 15 144 ' (32°) 6 (40°) 19 days (32° )....Dec. 8 t)3 Jan. 4 27 April 2 114 5.0 14 60 14 145 ") ( 70°) 6 ( 40° ) 19 days (32° )....Dec. 8 92 Jan. 3 28 April 8 119 5.3 16 77 14 146 ' (32°) 6 ( 40° ) 38 da ys (32° )....Dec. 27 88 Jan. 22 26 April 14 108 4.2 11 54 13 137 2 ( 32° ) 6 (40°) 38 days (32° )....Dec 27 89 _Ian. 21 25 April 20 114 4.8 13 66 13 12

Weight range for 7-inch bulbs is from 65 to 95 grams. (A.N. Roberts andNursers" Digest 3: 3-4. August 1959).

Cohlframed bulbs were moved to the greenhouse on November 24." Height was measured from soil to the leaf subtending the lowermost flower.

D. Calvin. Grading methods compared for lily bulbs. Oregon Ornamental ^:Int

going but they probabl y could have been brought in ontime. Plants of treatments 6 and 7 flowered in a shortperiod of time but were much too late for an earl y Easter.Although preheating always delayed flowering comparedto initial cold storage, it also increased the bud countslightl y and the leaf count much more. Plant appearance in

general was satisfactory:but all were columnar in

perhaps some were too short.habit.—L. T. BLANEY

<A.. N. ROBERTS

norticulture Department

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