Barnett, William W. : W. W. Barnett is Regional IPM Advisor, Kearney Agricultural Center, Parlier

Coviello Mr, Richard L.

Edstrom, John Paul

Zalom, Frank G

Insect pathogen â?? Bt â?쳌 controls peach twig borer on fruits and almonds William W . Barnett a John P . Edstrom CI Richard L . Coviello CI Frank P . Zalom considered relatively nondisruptive to present for larvae to tunnel into and Early season sprays of the insect biological control . Recently , growers and complete development in them . After pathogen Bacillusthuringiensis , consultants have reported dormant completing their development , mature were applied to peaches or â?? Bt , â?쳌 treatments less effective for PTB control PTB larvae seek sheltered areas to pu - and almonds to determine effi - than in the past . In addition , dormant pate . They emerge as adults in late treatments have come under scrutiny as March or early April and lay eggs . These cacy against peach twig borer the sprays are suspected of drifting to eggs , upon hatching , produce the first ( PTB ) . Data indicates one or two nearby crops and environmentally sensi - summer generation . Larvae of the first as Bt treatmentsduring bloom are tive areas . They have also been impli - summer and subsequent generations effective as a dormant organo - cated in killing raptors , including hawks , complete their development inside a phosphate plus oil spray for PTB present in orchards at the time of appli - single shoot or fruit . There are three or cation . four generations a year . control . Research is currently un - First instar PTB larvae construct over - Control of the first summer and later der way to determine the impact wintering sites , called hibernaculae , be - larval generations with stomach poisons on other pests . neath the bark in the crotches of 2 - and or insect pathogens has not been suc - 3 - year - old wood . Some PTB begin over - cessful because these larvae emerge The peach twig borer ( PTB ) , Anarsia wintering as early as August , and the from eggs and immediately bore into is a serious pest of many tree lineateIla , remainder enter these chambers as the shoots or fruit , failing to ingest a lethal crops grown in California . Hosts include season progresses . Larvae feed within dose of the toxic material . Overwintered peaches , nectarines , plums , prunes and PTB , however , are vulnerable to such the hibernaculae on warm days during almonds . For many years the recom - the winter and emerge as first or second materials because they emerge as first mended control for PTB has been to treat instars as trees begin to leaf out . After and second instar larvae and feed on overwintering larvae with an oil plus or - emerging , these larvae feed on new several different shoots before maturing . ganophosphate insecticide . In addition shoots and fruit buds , often as many as This paper describes our strategy to to being effective for other pests such as five or six , before maturing . Eventually , control overwintered PTB larvae using San Jose scale , a dormant treatment is as shoots elongate , enough soft tissue is the Kurstaki strain of Bacillus 4 CALIFORNIA AGRICULTURE , VOLUME 47 , NUMBER 5 Followup work has indicatedthat aerial sprays of Bacillus thuringiensisare not as effective as ground applications ; coverage Almond study thuringiensis ( Bt ) , an insect pathogen af - of leaves is insufficientand insect pests fecting only lepidoptera larvae . In addi - In 1990 , second - leaf ' Butte ' cultivar do not ingest enough Bt . tion to being selective , Bt is regarded as almonds were treated with 0.75 pound nontoxic to bees , humans and wildlife , per 100 gallons of Javelin WG at four dif - The first Bt treatment was applied and is considered safe for the environ - ferent treatment timings and one treat - March 1 , when trees were at early pink ment . Experiments were initiated to ment at all four timings for a total of five bud and shoots were 0.5 inch long . Ap - determine the potential for Bacillus treatments . The first treatment timing plications were repeated according to thuringiensis ( Bt ) to control PTB as an was at bud swell . Others were applied at our design with different combinations alternative to traditional organophos - 10 % bloom , petal fall and early leafing of timings at 7 - day intervals until after phate dormant treatments . These experi - stages . Included also was an untreated jacket split when shoots were 3 to 6 ments were conducted during the spring control and , for comparison , standard inches long ( fig . 1 ) . Rain fell during the of 1990 and 1991 in a peach and nectar - dormant treatments of 1quart formu - early part of the period , with 0.10 inches ine orchard near Kingsburg ( Tulare lated Supracide 2E plus 1gallon oil per March 3 and 0.24 inches March 12 . No County ) , and an almond orchard at the 2E plus oil 100 gallons and Supracide rain fell after March 12 . Nickels Soil Laboratory near Arbuckle with copper added were applied Febru - The treatments were evaluated by ( Colusa County ) . ary 20 . Treatments were arranged in ran - counting all shoot strikes April 4 . This domized complete blocks with 10single Peach and nectarine study of the first was before the beginning tree replicates . Sprays were applied to adult PTB flight . Oriental fruit moth Three - year - old ' Elegant Lady ' runoff at approximately 220 gallons per ( OFM ) was controlled by mating disrup - peaches and ' Sweet Home ' nectarines acre or 1.5gallons per tree , before and tion and few , if any , OFM shoot strikes were treated from one to five times and after bud break . were present in the orchard when PTB at different combination of timings with This study was repeated in 1991 on strikes were counted . 2.4 pounds per acre of Javelin WG , a third - leaf ' Butte ' cultivar almonds to re - commercial formulation evaluate the treatment tim - of Bacillus thuringiensis . ings and to test additional Eighteen combinations of combinations of treatment multiple applications and timings . For comparison , 1 treatment timings were pound formulated diazinon applied . For comparison , plus 1gallon oil per 100 gal - a standard dormant treat - lons was applied January 24 . ment of 3 pounds formu - Untreated trees were used as WP plus lated diazinon 50 controls . Treatments were 4 gallons of oil per acre arranged in a randomized was applied on February complete block with seven 20 and some trees re - single tree replicates . Dilute mained untreated as a sprays were applied to run - control . Treatments were off at 300 gallons per acre . arranged in randomized Treatments in both years complete blocks with four were evaluated in April be - single tree replicates in fore the development of first peaches and three in nec - summer generation larvae tarines . Treatments were by determining the total applied by handgun number of larval entries sprayer using 2 gallons of ( strikes ) of shoots per repli - material per tree . The trees were spaced cate . Treatments for both crops and Fig . 1 Impact of Bacillusthuringiensis by 16 x 18 feet apart , resulting in 150 trees within years for almonds were com - treatment time on Anarsia lineatellain nec - per acre . pared by analysis of variance , and tarines and peaches in Tulare County , 1990 . CALIFORNIA AGRICULTURE , SEPTEMBER - OCTOBER 1993 5 Fig . 2 Impact of Bacillus thuringiensis by treatmenttime on Fig . 3 Impact of Bacillus thuringiensisby treatment time on Anarsia lineatellain almonds in Colusa County , 1990 . Anarsia lineatellain almonds In Colusa County , 1991 . applied and compared with the standard junction with mating disruption for Ori - means separated by Duncanâ??s new mul - organophosphate - plus - oildormant ental fruit moth , there tiple range test . is a good possibil - treatment . ity that peaches , nectarines and prunes Peachhectarine results In 1991 , our results indicated that can be grown most years without using several timings could significantly lower Random shoot samples for PTB indi - e - broad - spectrum insecticides.At mini - the number of shoot strikes compared cated that first PTB larval emergenceb mum , this provides growers the optionn - with an untreated control.The best treat - gan March 9â??8 days after the first treat - of avoiding dormant sprays in enviro ment comprised three Bt applications:at ment date in the Kingsburgpeach and mentally sensitive areas . Used in econ - arly popcorn , petal fall and petal fall - plus - 2 - nectarine plot . junction with winter sanitation and weeks ( fig . 3 ) . Two sprays applied 2 harvest for navel orangeworm control , All treatment timings , except a single weeks apart at popcorn and petal fall application at the end of petal fall , re - broad - spectrum insecticidescan alsobe signifi - and at petal fall alone were not sulted greatly reduced in significantly fewer ( P < 0.01 ) in almonds . In orchards cantly different ( P > 0.05 ) from that of the shoot strikes than the untreated check where naval orangeworm parasites are diazinon - plus - oiltreatment . The other ( fig . 1 ) . The singletreatment at end - of - present , this may increasetheir effective - single - treatmenttimings had signifi - petal - fall , the jacket treatment , the ness because they would not be de - two cantly greater ( P < 0.05 ) shoot strikesfig . stroyed by dormant organophosphate treatments at the beginning and end of than the standard dormant spray ( 3 ) . and the single pink - bud treat - petal fall , sprays . Two applications of Bt for PTB con - ment were not significantlydifferent Discussion trol are somewhat more expensivethan than the single - jacketor end - of - petal - fall Although the 1990peach and nectar - a single organophosphate treatment , es - treatments ( fig . 1 ) . All the remaining ine orchard had not received insecticide pecially if application costs are consid - treatments were significantlybetter than treatments for6years , PTB abundance ered . However , Bt is compatiblewith the two single treatments at the end - of - would be considered â?? moderate . â?? At most fungicidesand can be combined petal - fall and jacket stage . The best this population level , one application of with brown rot treatments , applied at single treatment timing as measured by Bt at 20 % bloom or multiple applications pink bud and full bloom , or with shot the least number of shoot strikes was the PTB before petal fall provided control of hole treatments , applied at petal fall to one applied at early ( 20 % ) bloom ( fig . 1 ) . equal to a dormant Diazinon - plus - oil reduce application costs . The best overall treatment timing was application . Multiple Bt treatments in Although results look promising , wen two applications , at pink - bud and the almonds in both 1990and 1991provided consider them preliminary . Researchi beginning of petal fall . These and all control equivalent to the standard dor - large plots is under way to verify sthesee treatment timings with three , four or results , to gain experience with the u mant spray . Conditions in 1990resulted five applicationswere not significantly in a â?? compact â?쳌 bloom of short duration of this material on a large scale and to different ( P > 0.01 ) from one another or with little rainfall in both stone fruit and answer many other questions relating to from the standard organophosphate - antly almond trials . In 1991 , the almond outbreaks of secondary pests . Growers plus - oil treatment . All were signific interestedin testingthis approach should bloom period was protracted , and the ( P < 0.01 ) different from the untreated trial orchard received 12inches of pre - use it in moderationthe firstyear and de - check . termineits suitabilityfor their orchards . cipitation during the treatment period . Almond results In spite of these more challengingcondi - W . W . Barnett is Regional IPM Advisor , tions , Bt treatments at popcorn and petal Our results for almonds in 1990im - Kearney Agricultural Center , Parlier ; J . P . fall provided comparablecontrol to the showed most single application t Edstrom is Farm Advisor , Colusa County ; standard dormant treatment in 1991 . ings , as measured by PTB shoot strikes R . L . Coviello is Farm Advisor , Fresno Our data indicate that it may be pos - Z ) , were not significantly different ( fig . County ; F . P . Zalom is Director , Statewide sible for growers to substitute well - ( P > 0.05 ) than the untreated checks . IPM Project , and Extension Entomologist , timed Bt treatments during bloom for However , significantlyfewer strikes early season control of PTB . Used in con - UC Davis . were observed when four Bt sprays were 6 CALIFORNIA AGRICULTURE , VOLUME 47 , NUMBER5