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Citrus Fruit Size Studiesexperimental test of 2,4-D sprays toincrease orange and grapefruit fruit size

Wm. S. Stewart and H. S. Hield

Further tests with 2 ,4 -D sprays arenecessary before any recommendationsfo r their commercial use to increase fru itsize are justified.

It is not known if spraying costs willbe repaid by the resulting size increase.The effect of repeated 2,4 -D applicationsover a number of ye ars is not known.Some citrus trees, however, which nowhave been sprayed annually for threeyears show no inj ury. These plots are be-ing continued.

On the basis of 1 7 experiments per-

formed since May 1946, it appears that asingle 2,4-D spray applied anytime fromseveral weeks before flowering to threeto four months afterwards can increasethe fru it size of the coming year's crop .Spraying with 2,4-D during this periodnot only increased fruit size but length-ened the growing period-hence delayedmaturity-and reduced the numb er offruits. Although the number of fruit s wasreduced, box production was not neces-sarily lowered since, because of the sizeincrease, fewer fr uits were required to filla box.

Application of 2,4-D as describedherein is expected to shift the productionpeak about one packing size toward lar gersizes. Since the diameter difference be-tween packing size 238 and 252 is onlyone eigh th of an inch, this increase willprobably not be apparent unless a largenumber of fruits are measured or thepackout statement obtained fo r fruit fromtreated and nontreated trees in the samegrove.

The f rui t size effect of 2,4-D is morepronounced on trees five to 10 years old

than on older ones. The same treatmentmay be used on young or old trees. Noadvantages have been observed as a re-sult of spra ying trees less than five yearsof age with 2,4-D.

It is possible that resultant curling ofyoung leaves on very small young treeswould retard their growth. There is noapparent advantage, and a possible dis-advantage, in 2,4-D spraying of recentlytop-worked trees which have just a fewvery vigorous growing shoots.

The concen tration of 2,4-D to use i nthe spray is determined by the time of

-Amounts of 2,4-D weed killing preparations to add to 50 0 gallons of water to prepare 2,4-D sprays

of from 16 to 40 ppm. One fluid ounce (fl. 02.) or 30 cubic centimeters (cc.) or 30 milliters (ml.) equalapproximately two level standa rd tablespoons.

FORMULATION *

Amount of 2A-D to add to 500 gallons'and time of applications

6 % eeks 8-12 weeks 12-14 weeks 14-16 weeksbftw after after after

16 ppm 24 ppm 32 ppm 40 ppm

flowering flowering flowering flowering

Dow Formula 4 0FI. oz.Cc. or ml.

2 3 4 560.8 91.2 121.6 152.0

Thompson's liquidWeedicide ConcentrateFI. oz. 2 3 4 5

Cc. or ml. 60.8 91.2 121.6 152.0Esteron 44FI. oz.Cc. or ml.

2 !h 3% 5 6%77.0 11 5.5 154.0 192.5

Weed-no-more 40FI. oz. 3 4 /2 6 7 /aCc. or ml. 95.0 142.5 190.0 237.5duPont 46% isopropyl esterFI. oz. 2 !h 3 4 5 6Cc. or ml. 75.8 113.7 151.6 189.5

To prepa re smaller amounts use proportionately less materia l. For example, to prepare 100 gal-lons of spray use 1/5 the above amounts; to prepare 20 0 gallons, use 2/5 the above amounts, etc.

*' These are furnished as a convenience to th e grow er. No ecommendation of one prepa ration overanother i s intended or implied. Of necessity this list i s incomplete. Other 2.4-D formulations besidethose listed here would be equally satlsfactory for the experimental use of 2.4-D to increase citrusfruit size.

application after flowering. The follow-ing concentrations of 2,4-D are suggestedfor experimental use to inc rease fruit sizeof Navel and Valencia oranges and grap e-fruit:

Time of applicationConcentratio n of 2,4-D in spray

4- 8 weeks afte r flowering. . . . 16 pprn( parts per million)

3-12 weeks after flowering. . . . 24 pprn12-14 weeks after flowering. . . . .32 ppm14-16 weeks after flowering. . . . 40 ppm

According to this schedule, if fullbloom occurred during the first week ofApril, then the 16 pprn 2,4-D spray shouldbe applied during May, or the 24 pprnduring June, or the 32 pprn during thefirst half of July, or the 40 ppm the lasthalf of July. Applications d uri ng this lastperiod seem to be the least likely to in-duce significant size increases.

These sprays probably will not lowerquality of either ora nges or grapefruit.However, if higher, excessive concentra-tion s of 2,4-D ar e applied, qu ality willprobably be lowered to such an extent

that th e f rui t are worthless culls althoughof extremely large size. The poor qualityis owing to a thick, rough peel; enlargedoil glands in the rind; large rudimentaryseeds ; xcessively large protr uding navelsin Navel oranges; a cylindrical fruit-shape; and grapefruit and Valencia or-anges with rudimentary navels.

In districts where an early market issought 2,4-D sprays for size increasewould be undesirable because of the ma-turity delay. Also, certain q uality factorsimprove with maturity. Thus, 2,4-D-sprayed trees harvested at the very be-ginn ing of t he season may have lowerquality than nontreated fruit or than ifharvested later.

The 2,4-D spray may be prepared forexperimental use by diluting 2,4-D weedkiller prepar ation s. The liquid 2,4-D weedkilling formulations, such as esters andamine salts, are preferred to the powdertypes since the liquid form s become rap-idly and unformly dist ributed throughoutthe spray mixture. Further d ata than nowavailable may show ester f orms of 2,4-Dto be more efficient than the amine salts.

The amounts of several of the weedkilling 2,4-D preparations to use for prep-

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PHOSPHATEContinued from page 11

concentrations g reater tha n 0.50 ppm de-ficiency is unlikely to occur-only twoout of 30 soils gave a response.

In the ligh t of field an d greenhouseresults, the following ranges of phosphatein water extract are suggested for tenta-tively defining the status of available

phosphorus in a given soil.Class 1. Response likely, less than 0.30

parts per million of phosphate.Class 2. Response uncertain, from 0.30

to 0.50 parts per million of ph osphate.Class 3. Response unlikely, greater

than 0.50 part s per million of phosphate.It must be emphasized that these rangesof phosphate are expressed on the solu-tion basis.

An anticipated response to phosphatefertilization implies that only phosphoru sis the limiting element and that thereexists no toxic condition in the soil. InCalifornia often nitrogen must be addedto secure a phosphate response.

In the case of a phosphorus-deficientsoil, response can be expected only whensufficient amounts of phospha te have beenadded. In th e case of a soil containingminerals of the kaolinite type, fixationwould be. great. This would require con-siderably more phosphate for a responseor a band ing of the fertilizer in the im-mediate vicinity of the roots.

The ranges of phosphate suggested forinter pretation of the chemical extr actionapply only to the crop s listed, mainly pas-

Field experiments suggest that theseresponses are especially pronounced forwinter crops.

' tures, field crops and truck crops.

Frank T . Bingham is Senior Laboratory Tech -nician, Division of Soils, in the ExperimentStation, Berkeley.

The above progress report is based on R e-search Proje ct N o. 1157.

CLINGSContinued from page 9

is becoming moist is to compare the ther-mometer readings.

Because of the large tr immin g losses-pits and peel-the over-all drying ratio isless favorable than for other fruit. Agood quality fruit dries about 9 : l and ahigher ratio is found for orc hard run lots.

To complete the reduction of moisturecontent to abou t 2O7hy the fru it is re-moved from the dehydrater and allowedto stand fo r several hours.

In foggy climates this plan can not befollowed, for standing fruit might actu-ally absorb a dditional moisture fr om theair. In such places, the temp erature at thefinishing end of th e tunnel is reduced toabout 150" F and the drying finally com-pleted while the frui t is still in the tunnel.

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The cooled fruit is removed from thetrays to clean, wooden boxes for tempo-rary storage before shipping.

Herman J . P h af l is Assis tan t P ro fesso r o fFood Technology and Assistant Microbiologistin the Exper imen t S tat ion , Berkeley.

Emil M . Mrak is Professor of Food Technol-ogy and Mycologist in the Experiment Station,Berkeley.

The above progress report is based on R e-search Project No. 1255.

CITRUSContinued from page 10

aration of 500 gallons of 2,4-D spray aregiven in the accompanying table.

Experimentally the sp ray has been ap-plied as a complete coverage spray offrom 15 to 20 gallons per tree to a s littleas abo ut six gallons per tree. Applicationsof f ou r gallons per tree o r less do notappear to be satisfactory at the concentra-tion s listed. It seems reasonable to expect

that spray-dusters, boom sprayers, orother equipment a pplying at least six gal-lons per tree of the 2,4-D sprays listed,would be satisfactory.

Much more information is needed onapplication methods before more thanthese tentative conclusions may be drawn.

Inasmuch a s 2,4-D used to reduce ma-ture fruit drop has been found to becompatible with the usual spray chemi-cals it seems likely tha t when used atsomewhat higher concentrations for fru itsize increase it will likewise be compatible.

When applying 2,4-D, it seems desir-able to reduce the curl ing of the newyoung leaves by delaying application un-til after the spring leaf growth has oc-curred. In some trials, although leafcurling has been severe, it has not reducedprod uction of fru it quality. Succeedingleaf growth flushes usually have app earednormal.

Spra ying Valencia oranges and grape-fruit with 2,4-D to increase fruit size ofnext season's crop has not been found toincrease frui t size of the cur rent , maturecrop. It will, however, effectively reducemature frui t-dro p of the curren t crop.

Trial s are now in progress to compare

2,4-D with 2,4,5-T (2,4,5-trichlorophen-oxyacetic acid) and other chlorinate dphenoxy acids for effectiveness in increas-ing fruit size. Preliminary data indicatetha t 2,4,5-T is at least a s effective as 2,4-D.

The over-all effect of 2,4-D spray s toincrease citrus fruit size seems to be anaccentuation of the juvenile character-istics of the fruit. Th is includes large fru itsize, delayed maturity, dar k green youngfruit; somewhat rough, pebbly rind tomaturity; and thick fruit-stems.

W m . S . S t e w a rt is Associate Plant Physiolo-gist in the Experiment S tation, Riverside.

H . S. Hield is Senior Laboratory T echnicianin the Experiment S tation, Riverside.

SPINACHContinued from preceding page

trace of fun gus penetration or develop-ment. The freedom from disease, then,can be considered to be true immunity,rather than high-level resistance.

The consistent reaction of the immunestocks during the winters of 1 9 4 7 4 8 and194-9, have not suggested the presence

of any physiologic stra ins of th e fungusin the Davis areas, although there wasample opportunity for infection from nat-ural sources through out the course of theexperiments.

Because of the predominantly dioecioushab it of spinach, self-pollination is notnormally possible. Inheritance data,therefore, have been secured on the firstgeneration resulting from the cross be-tween immune and susceptible plants andon the first backcross of immune first gen-eration plants to the susceptible types.

The results of these experiments haveshown that immunity is simply inheritedas a single dominant genetic character.Because of this, i t will be possible totransfer to commercial spinach varietiesthe complete freedom from downy mil-dew which has been found in the Iran ianvariety.

Pau l G . Sm ith is Assistant Professor of TruckCrops and Assistant Olericulturist in the Ex-periment Station, Davis.

The above progress report is based on Re-search Project No . 906.

TIMBER

Continued from page 7Whitaker's Forest is situated in one of

the most productive timber types in Cali-fornia. Sugar pine, ponderosa pine andwhite fir are all important timber trees,and the sequoias he re have demonstratedthei r ability to grow in height and volumeat a r ate exceeding tha t of most softwoodtree species.

The east portio n of the forest abovethe camp clearin g is cooler and somewhatmore moist than the west portion andcontains a mixed stan d of suga r pine,white fir and sequoia with occasional in-

cense cedars and black oaks.Ponderosa pines appear in greaternumber towards the west with increasein warmth and dryness and the sequoiasdrop out of the stand before the westboundary is reached.

From there west on the National Forestthere are virtually no sequoias at thiselevation. A heavy stand of mature pon-dero sa pine on the ridge west of the prop-erty produced a larg e volume of timberwhen cut under National Forest timbersale in 1944 and 1945.

Wo odbridge Metcalf is Extension Foresterand Ass ociate Professor of F orestry in the Ex-periment Station, Berkeley.

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