Sibbett, G. Steven : G. S. Sibbett is Farm Advisor, Tulare County

Van Steenwyk, Robert A. : R. A. Van Sfeenwyk is Extension Entomologist, Department of Entomology, UC Berkeley

Moreover , shredding is not always com - patible with a growerâ??s cultural pro - gram ; that is , in cultivated orchards , un - even ground and clods can preclude complete destruction of the nuts . Other orchard floor management strategies and their effect on NOW survival within the nut ( that is , laying nuts in sod or weeds throughout winter or disking mummy nuts into the soil ) have not been explored until now . If such prac - tices were proved effective in destroying overwintering NOW , growers would have more flexibilityin orchard sanita - tion . Here , we report the results of a 2 - year study that evaluated effects of these orchard management practiceson the sur - vival of overwintering NOW larvae and pupae in mummy walnuts on orchard floors . Portervilleexperiment The experiment was conducted in Porterville , California , during the winter and spring of 1990 - 1991and 1991 - 1992 in a mature â?? Serrâ??walnut orchard with a Trap apparatusfor collecting emerging navel orangeworms ( berm treatment ) . history of economic NOW damage . Na - vel orangeworm infestation in mummy walnuts was estimated in the orchard each year . Each December , approxi - mately 100pounds of mummy nuts were collected from the orchard . Twenty Shredding â?? mummy â?쳌 random samples of 10nuts each were chosen from the entire lot . These samples were inspected for NOW larvae walnuts is key to destroying and pupae to estimate the percentage of NOW infestation . In 1990 - 1991,27 % of the nuts were infested with one or more navel orangeworm in winter NOW pupae or larvae ; infested nuts had an average of 1.2k 3.0 NOW larvae and pupae per mummy nut . In 1991 - 1992 , G . Steven Sibbett D Robert A . Van Steenwyk 30 % of the nuts were infested but with 0.3 f0.4 NOW lar - fewer insects per nut , minimize disease , injury from insects Winter orchard sanitation is a vae and / or pupae per mummy nut . and physical damage that would pro - major component of navel In 1990 - 1991,250randomly selected vide entry sites for infestation . Once hull orangeworm ( NOW ) control in nuts and in 1991 - 1992,500randomly se - split occurs , growers must harvest the lected nuts underwent one of four treat - crop promptly to prevent infestation . walnuts . â?? Mummy â?? nuts remain - ments : ( 1 ) Nuts were placed on a weed - Postharvest operations call for orchard ing in the trees shelter overwin - free â?? berm â?? ( to simulate weed - free , bare and equipment sanitation , removal of tering NOW . Once nuts are re - ground ) . ( 2 ) Nuts were placed in resi - trash nuts from the huller / dehydrator moved from the trees , shredding dent weed cover ( 3to 4 inches high at and destruction of unharvested nuts to to destroy the protective shell en - time of placement ; wet weeds were ex - remove sites where NOW larvae and pu - pected to rot nuts which harbored pae can overwinter . This procedure re - sures maximum NOW mortality . NOW ) . ( 3 ) Nuts were placed on the or - duces the number of overwintering chard floor and shredded with a flail NOW and the potential for infestation Navel orangeworm , Amyelois transitella shredder . ( 4 ) Nuts were placed on the the following year . ( Walker ) , is one of the most devastating orchard floor and disked in two direc - Orchard sanitation is a major compo - pests of walnuts grown in California . tions . Each treatment was replicated nent of NOW management and control Damage results when its larvae infest four times . Thus , according to pretreat - in walnuts . It includes shaking trees dur - nuts following hull split before harvest . ment crack - out , approximately 300 ing the dormant season to remove previ - Economic loss to the walnut industry NOW larvae or pupae in 1990 - 1991 and ously unharvested â?쳌 mummy â?쳌 walnuts . was estimated at $ 12 million in 1990and 200 in 1991 - 1992 were placed into each Following shaking , nuts should be $ 9 million in 1991 . replicate of each treatment . shredded to destroy the protection of - A year - long control program is re - The nuts underwent their respective fered to NOW by the walnut shell . quired to manage navel orangeworm treatments December 20 , 1990 , and De - Not all walnut growers have shred - ( NOW ) . Navel orangeworm cannot in - cember 4,1991 , in the orchard where ders capable of destroying the nuts and fest sound , uninjured nuts during the they were collected . Following treat - must rent or contract for this service . growing season , as long as growers CALIFORNIA AGRICULTURE , VOLUME 47 , NUMBER 5 26 ment , they were covered by a mesh Rainfall was measured throughout pyramid cage , the experiment . In 1990 - 1991 , little rain - 1m x 1m square at the proximately 24 % and 20 % , respectively , fall occurred , and two midwinter irriga - base and 1m high . Each cage was of the NOW population . No parasites tions were applied to simulate the equipped with a 1 - quart canning jar af - 10 emerged from the laboratory samples in fixed to the apex of the pyramid to col - inches of winter rainfall the area normally either year . lect adult NOW moths . Following the In 1991 - 1992 , about 11inches of receives . Effects of orchard floor disking treatment and cage placement , rain fell , a more normal rainfall pattern . any nuts lying outside of the cageâ??s 1m 1991 . Significantly higher NOW Laboratory emergence x 1m dimensions were carefully placed moth emergence occurred when under the cage in the same position rela - One sample of nuts , retained each mummy nuts were placed on the bare , tive to their depth of burial . Each cage year , was held under ambient laboratory weed - free berm than when placed in was monitored for adult NOW emer - conditions to observe adult NOW emer - weeds , disked or shredded ( table 1 ) . gence at 2 - week intervals during the gence and any parasite activity . In 1990 - Mummy nuts placed on the bare berm winter . Once emergence began , cages 1991 , 127nuts containing approximately yielded an average of 63.3 adult NOW were monitored weekly for adult emer - moths per replication . This compares 150 NOW larvae and pupae were re - gence from March 29 through June 19 , with an average of 8.8,2.3 and served to observe emergence in the labo - 0 NOW 1991 , and from March 11to June3,1992 . ratory ; in 1991 - 1992,300nuts containing adult moths emerged from mummy nuts The average number of NOW adult approximately placed in weeds , disked or shredded , re - 81 larvae and pupae were moths that emerged was analyzed by observed . spectively . Percent recovery from the ANOVA ( analysis of variance ) and In 1990 - 1991,36 adults emerged un - initial population was 21 % , 3 % ( 97 % re - means were separated by Duncanâ??s mul - der ambient laboratory conditions , and duction ) , 1 % ( 95 % reduction ) and 0 % tiple range test , P 5 0.05 . in 1991 - 1992,16adults emerged , ap - ( 100 % reduction ) , respectively . 1992 . As in 1991 , the highest emer - gence occurred when mummy nuts were placed on the bare , weed - free berm . However , unlike 1991 , no significant dif - ference in emergence was detected be - tween nuts placed on the bare berm or in weeds . Adult NOW emergence from nuts placed on the bare berm or in weeds was significantly higher than when nuts were disked or shredded . Av - erage moth emergence from shredded nuts was significantly lower than those disked ( table 1 ) . Nuts placed on the bare CALIFORNIA AGRICULTURE , SEPTEMBER - OCTOBER 1993 27 Domestic , world market growing . . . berm or in weeds averaged 11.8and 9.0 moths per replication , respectively . 3.8 Disked nuts yielded an average of moths per replication . Emergence from shredded mummy nuts was 0.3 ( onenut was found intact followingthe shred - ding treatment ) . Percent recovery from Grape juice concentrate - 5.9 â?쳌 / , the initial population was low 4.5 % ( 24 % reduction ) , 1.9 % ( 68 % reduc - emerging as a sweetener in tion ) , and 0.2 % ( 97 % reduction ) for berm , weeds , disked or shredded , re - spectively , compared with 1991 . It is un - juices , food products known why this discrepancy occurred . In the 1991 - 1992winter , rainfall ewass relatively normal , and temperatur Dale Heien 0 Ray Venner were more moderate than in 1990 - 1991 , when a severe freeze occurred in mid - December followingplacement of thender nuts in the orchard . Interestingly , u laboratory conditions , NOW adult emer - gence was relatively similar each year . sweetensjams and jellies , yogurt , frozen These results are unlike those ob - The domesticand world market fruit desserts , cereals , cookiesand other tained for almond , which has a rela - for grapejuice concentrateis soft shell compared with walnut . tively bakery products . Fruit concentratesare growing . We discussseveral op - LittleNOW survivaloccurredin mummy replacing table sugar and corn syrup as tions that may enable the San almonds allowed to remain ina weedy many consumers perceive fruit concen - cover throughout winter . Disking also trate as a healthier sweetener . Consum - Joaquin Valleyâ??sgrape industry to resulted in considerablybetter NOWThe ers favorably view products labeled â?? no capture a larger share of this mortality in almond than walnut . sugar added . â?쳌 In 1989 , when white growth market . thicker walnut shell apparently offers grape juice concentratesold for $ 4.50 a considerablymore protection than does gallon , the costs of grape juice oconcen - w , the almond shell . trate and table sugar were similar . N Grape juice concentrate , an emerging grape juice concentrateis slightlymore growth industry , is used in making Conclusions grape and multifruit juices and in sweet - expensive . U.S . , total - Winter orchard sanitation is essential Sparklingjuice sales in the ening food products . Production in Cali - fornia increased to approximately to NOW management in walnut or - ing 37.3million gallons in 1989 , are chards . However , simply removing 462,000 tons in 1991 , accountingfor 28 % growing 15 % annually . Sales of spread - of the 1991SanJoaquin Valley crush mummy nuts from the trees does not able fruits are also increasing at the ( grape districts 12 , 13 , and 14 , see map ) . destroy overwintering larvae and pupae same rate . Demand for products con - and prevent subsequent adult emer - The concentrate , produced by heating taining fruit concentrateis expected to grape juice under a vacuum to remove gence . Our data show that adult NOW continue . water , competeswith apple and gotherar , readily emerge from intact nuts shakena U.S . grape juice concentrateis prima - n fruit juice concentratesas well as su from trees and allowed to remain on rily supplied by several varieties grow mainly on a price basis . dry , weed - free orchard floor . Shredding in the SanJoaquin Valley and by the San Joaquin Valley grape growers mummy nuts followingtheir removal Concord variety in New York and other 1presents basic generally view concentrateas a market from the trees essentiallyeliminates all northern states . Table for surplus grapes , just as wine was once U.S . grape juice concentrateproduction NOW survival . Disking nuts into the a market for grapes not marketed as soil , or allowingnuts to remain in a and trade . table grapes or raisins . Over time the The price of grape juice concentrateis weedy cover reduces emergencebut wine market has relied increasinglyon does not eliminate it ; a few nuts in strongly affected by the worldwide sup - wine - specificvarietal grapes and on ply of apple juice concentrate , which ac - each situation probably remain ex - grapes grown in Californiaâ??scoastalar - counts for approximately 72 % of US . posed and relatively dry , allowing eas . Today , the grape juice concentrate fruit concentrateconsumption . Apple NOW to survive . market is filling the surplus grape mar - and grape are close substitutes forpple Our data offer little flexibilityin man - ket role . Just as grape production multifruit and sparkling juices . A aging mummy nuts to eliminate NOW overwintering , once nuts are shaken changed in response to wine industry juice concentrateprices fluctuate with from trees . Shredding remains the bestuc - demand , grape production for concen - the level of apple juice concentrateim - method for ensuring maximum destr U.S.appleex - trate could become a primary market fore ports and the amount of the crop processed into concentrate.For tion of larvae and pupae in a walnut San Joaquin Valley growers . This articl ample , in 1991 , the prices of all fruit con - sanitation program . examinesthe prospects and problems in centrates rose substantially as rfewerate making this transition . apples were diverted into concent The concentratemarket G . S . Sibbett is Farm Advisor , Tulare due to fears surrounding the use of the County , and R . A . Van Sfeenwyk is Exfen - Grape juice concentrateis diluted growth regulator Ajar . The price of sion Entomologist , Department of Entomol - into single - strengthgrape juice and apple juice concentratein 1993plum - ogy , UC Berkeley . multifruit and sparkling juice . It also meted because of bumper apple harvests 28 CALIFORNIA AGRICULTURE , VOLUME 47 , NUMBER 5