Cowles, Richard S. : R.S. Cowles is former Assistant Entomologist, Department of Entomology, UC Riverside and current Assistant Entomologist, Connecticut Agricultural Experiment Station, Valley Laboratory, Connecticut

Donaldson, Dean

Varela Dr, Lucia G.

Left , needle distortions caused by the Cooley spruce gall adelgid feeding on Douglasfir and white waxy material left by females . Above , yellow spots on the upper side of the needles are caused by adelgids feeding on the underside . control Swina insecticidetreatments - I - J adelgids on Douglas fir Lucia G . Varela o Richard S . Cowles o Dean R . Donaldson fringe . Nymphs molt in approximately secticides are registered for aphid con - Insecticide applications made to 1week and become adults . They then trol , but there is a lack of comparative Douglas fir Christmas trees vary begin to lay eggs under heavy waxlike data on their efficacy in controlling in their ability to suppress Cooley strands . Egg laying continues for ap - Cooley spruce gall adelgid . This study spruce gall adelgid , a sucking in - proximately 1month . In our observa - was undertaken to compare registered sect that causes needle distortion tions , the average number of eggs laid materials , including a new systemic A field experi - and discoloration . was 44 . Eggs begin hatching 2 to 3 insecticide , and to explore the use of ment in Napa County showed that weeks after being laid . One percent horticultural oil as an inexpensive and organophosphate systemics are egg hatch was noted in early March , less toxic alternative to conventional ineffectiveat controlling adelgids , and 95 % egg hatch was recorded by synthetic insecticides . but imidacloprid , a newly regis - mid - April . tered systemic insecticide , is Adelgid life cycle Newly hatched ( first stage ) nymphs highly effective . Horticultural oil is are light brown with a darker head . usu - The Cooley spruce gall adelgid effective , but causes slight needle They are called crawlers because they ally alternates generations between yellowing . Thisside effect can be move until they find a suitable place to spruce ( the primary host on which mitigated by precisely timing the settle . The majority of crawlers do not these insects form galls and then un - oil application before bud break settle until the new foliage emerges . dergo sexual reproduction ) and Doug - when the overwinteringadelgids This new growth becomes available to las fir ( the alternate host on which are transforming to adults but be - crawlers at different times on indi - they reproduce asexually ) . Alternation vidual Douglas fir trees , which are fore they lay eggs . of generations between these two seed propagated and are genetically hosts is not essential for insect survival variable . Douglas fir in Napa during or population increase . In Napa The Cooley spruce gall adelgid , 1994and 1995began spring growth County , we have only observed the Adelges cooleyi ( Gillette ) , can be a seri - over a period of about 5 weeks . Earli - asexual cycle in Douglas fir Christmas ous sucking - insect pest on Douglas firs est terminal bud break began during tree farms . grown in Christmas tree farms and in the third week in March ; the latest bud Adelgid nymphs overwinter on the forest tree nurseries . High populations break occurred in the last week in current yearâ??s growth of Douglas fir can cause severe needle distortion and April . needles ( fig . 1 ) . The overwintering chlorotic spots rendering the trees un - Once crawlers move to new growth nymphs are dark brown in color and marketable . There is little information they gradually darken and secrete a are heavily sclerotized ( the hardening on the best method and timing for the white waxy fringe around the edge of of their exoskeletons ) . In mid - February control of this pest under California the body . They become flattened , with the nymphs start secreting a waxy conditions . Presently many labeled in - CALIFORNIA AGRICULTURE , VOLUME 50 , NUMBER 5 34 ii u x - - m Y 1 7m Heavily sclerotizedoverwinteringadeigid nymphs . Femalewith eggs under heavy waxlike strands . mer , fall and winter . Nymphs are the legs folded under the body , and fix themselves firmly to the leaf surface . more prevalent on the north side of the tree . Nymphs that survive the The second - stagenymphs are light brown and the body is covered with a summer are generally found at the - Y waxlike secretion.Nymphs soon base of the needle or below the tuft of iJ > . - change to egg - laying adults covered waxy strands left by the female . Feed - Ym x ing continues throughout the summer , with curled waxy strands . Adults were 7m as evidenced by a droplet of honey - seen about 10days after crawlers Adelgid crawler ( left ) and settling nymph dew secretion at the rear of the settled on the new growth . It is this ( right ) with a droplet of honeydew secre - spring - generationfeeding by the nymphs abdomen . By late October the of its abdomen . tion at the rear nymphs and adults on the newly ex - nymphs are heavily sclerotized , no se - cretions are visible and the nymphs panded needles of Douglas fir that causes the greatest damage . High are firmly embedded in the needle on and 4 trees ( 5to 8 feet tall ) per plot populations cause needles to become either the upper or lower side of the with high adelgid populations were distorted and discolored ; yellow spots base of the needle . When on the upper selected for season - long monitoring . appear at sites where insectshave fed . side of the needle , they embed them - Adelgid control was evaluated us - selves on the middle vein . Summer - generationadults begin ing two systems : insect count rating laying eggs in early - to - mid - Mayand and visual rating . Both systems were Systemicsand oil combinations produce only a quarter the number of used on March 25 and June 20 to de - eggs ( average 12per female ) that the A field experiment was conducted termine whether their results were first generation produces . Crawlers with 2 acres of Douglas fir trees consistent . The count rating system appear 2 to planted in 5 - feet - by - 5 - feetspacing on 3 weeks after egg laying is was designed to provide more infor - observed ( late May to early June ) . Be - Haire loam soil located near Napa . We mation than a presence - absencerating cause the needles harden as summer divided the field into 4 blocks and system , and generated data amenable progresses , the development of the each block into 14 insecticide treat - to analysis using methods designed second generation is prolonged and ment plots ( table 1 ) according to a ran - for other 0 - to - 100 scales , such as per - centages . there is high nymphal mortality . domized completeblock design . Each Adelgids remain in heavily sclerotized plot had approximately 50 trees , 3 to For the insect count rating , we ex - amined the first immaturestages through the late sum - 10 feet tall . The entire plot was treated 7 inches of the tips of CALIFORNIA AGRICULTURE , SEPTEMBER - OCTOBER 1996 35 10branches from each sample tree for egg hatch , we took samples twice a Timing of oil treatment the presence of adelgids . Adelgid week . Sprays were applied with a numbers were rated by assigning each hand - held nozzle to run - off , using ap - Because some March 1994 treat - shoot a score of 0 , l or 10 . No adelgids proximately 400 gallons of water per ments caused a slight yellowing of present on a shoot scored 0 , one acre . Controls were sprayed with Douglas fir needles , we applied follow - adelgid present was assigned a score water . up oil treatments the second year on of 1 and shoots with two or more Nontransformed ratings on March Feb . 17 , 1995 . This spray was applied adelgidswere assigned a score of 10 . 25 and square - root transformed post - before the appearance of tender new The jump in rating from 1to 10reflects treatment ratings of adelgids on growth of shoots , when overwintering the typical presence of aggregations of sampled trees were subjected to analy - adelgid nymphs had just begun form - adelgids when treatments were inef - sis of variance to detect differences ing wax but before the females started fective , and provides a convenient between insecticide treatments . Mean to lay eggs . Applications timed this 0 - to - 100point rating for each tree separations were done with the way catch the adelgids during an ac - when the 10shoot scores were totaled . Student - Newman - Keuls test . tive growth phase when they are most Insect count ratings were done on Feb . 24 ( pretreatment count ) , March 25 , June 2 and June 20 . For the visual rating , each sample tree was rated from 0 to 5 . A minimum score of 0 was assigned when no adelgid was visible when the canopy was opened three times . Opening the canopy involved spreading the branches to inspect the interior of the canopy.A score of 1 was assigned when adelgids were visible within the canopy but not on the outside . Scores of 2,3 and 4 corresponded to less than 15 % , 45 % and 75 % of the branches in - fested with adelgids , respectively.A maximum score of 5 was assigned when adelgids were visible on more than 75 % of the canopy . The visual rat - ings were done on March 25 , June 20 and July 25 . Phytotoxicity was rated on the sample trees on July 25 . Since discol - oration was uniform , those trees with no discoloration were rated as 0 ; those with yellow - greendiscoloration were rated as 1 . Granular pesticide treatments were applied first to allow time for systemic uptake . The two granular treatments , imidacloprid ( 0.4lb ai / ac ) and disulfo - ton ( 6.5lb ai / ac ) , were applied March 4 and 5 in a grid of 2 - inch - deepholes , 2 ' / 2 feet apart . To activate the insecti - cide , the field was irrigated the day af - ter treatment . One row of trees on all four sides of the plot was left un - treated as a buffer . Sample trees in all plots were at least two trees away from the buffer zone . Foliar spray treatments were ap - plied between April 28 and May 2 , timed at maximum egg hatch and be - fore wax formation was observed on newly hatched adelgids . To estimate CALIFORNIA AGRICULTURE , VOLUME 50 , NUMBER 5 36 sensitiveto pesticides ; this treatment ticidal effects lasting into the year fol - oxythioquinox , diazinon and diazinon opportunity window lasts only about lowing application ( data not shown ) . + oil . The poor performance of the 7 days . The soil application of imidacloprid diazinon + oil combination is para - Eight paired adjacent trees with granules at agricultural use rates ( 0.4 doxical , since horticultural oil by it - similar size and adelgid infestations lb ai / ac ) resulted in continued move - self was one of the more effective were selected for treatment . One tree ment into test trees through the sum - treatments . of each pair was treated with 2 % oil mer , as indicated by the steady decline Oil by itself or in combination with and the other with water as the con - in adelgid counts . The low dosage and any insecticide was phytotoxic to Dou - trol ; the spray volume was 400 gallons soil application should minimize the glas fir in the 1994 trial ( table 2 ) . The per acre . For pre - and posttreatment hazard ( relative to foliar sprays ) to symptom of damage was uniform dis - ratings of adelgids , we used the insect beneficial predators or parasites . Most coloration of needles throughout the count system . Pretreatment counts beneficials do not feed on plant tissue tree , changing from the normal blue - were done on Feb . 14 and posttreat - containing the insecticideso they green to yellow - green.This slight discol - ment adelgid populations and phyto - would not contact residues . Further orationremained for the entire season . toxicity were rated on March 4 and studies are needed to confirm this . Needle discolorationwas not visible in April 18 . The effect of oil on adelgid Application below the soil surface new growththe followingyear . mortality was analyzed with a paired in this trial was accomplishedwith The 1995oil treatment timed to t - test . granular formulations by placing a avoid the new growth gave moderate measured dose in a planting bar hole adelgid control ( table 3 ) . However , Varied effectiveness between each two trees within the older growth needles turned yellow - As shown in table 2 , insecticides row . Sprayable formulations , such as green within 48 hours after the oil ap - varied in their ability to suppress the flowableimidacloprid product plication in all the treated trees . Once Cooley spruce gall adelgids . The two now registered for use in Christmas the new growth covered it , needle dis - rating systems were highly correlated tree plantations , could be applied effi - coloration was no longer noticeable ( r2 = 0.78 with one outlier , March 25 ciently through precision soil injection and appeared to affect neither tree data ; r2 = 0.93 , June 20 data ) , which re - devices.These techniques lead to growth nor needle shedding . sulted in consistent measures of pest minimal exposure of applicators and Effectivetreatment options populations , including similar ranking wildlife to insecticides , and should be and statisticalseparation of treatment investigated in further trials . Subsur - Effective treatments that did not means . face application does not require ex - cause phytotoxicity were ( ranked in Except for disulfoton and acephate , pensive equipment , nor does it require order of decreasing efficacy ) : two systemicorganophosphate insecti - smooth ground suitable for driving imidacloprid , carbaryl , chlorpyrifos cides , all treatments demonstrated tractors or sprayers . This is a distinct and fluvalinate . Horticultural oil sup - some degree of suppression of Cooley advantage , considering that many pressed adelgids but also caused spruce gall adelgids . Christmas tree plantations are small Douglas fir needle discoloration . If oil Effective control of Cooley spruce farms or are located on rough terrain . is applied after bud break , the discol - gall adelgid was obtained with the fol - Carbaryl , a persistent carbamate in - oration is visible at harvest . If oil is ap - lowing treatments : imidacloprid , car - secticide , often induces secondary out - plied in the very narrow time frame baryl + oil , carbaryl , chlorpyrifos + oil , breaks of spider mites by eliminating before bud break , when the overwin - fluvalinate , fluvalinate + oil , chlor - mite predators . The spruce spider tering adelgids are transforming to pyrifos and oil . Oil enhanced the activ - mite , Oligonychus unuquis , is a par - adults but before they lay eggs , needle ity of carbaryl and chlorpyrifos , pro - ticularly damaging species to Douglas discoloration occursbut is later viding excellent early - to - midseason fir . Therefore applications of carbaryl masked by new growth . In this case control of adelgids . without oil might require additional discoloration is not visible at harvest . Imidacloprid , an insecticidere - miticide sprays later in the season . cently registered in California , has un - Chlorpyrifos or fluvalinate applied L.G . Varela is North Coast Integrated Pest usual properties that may make it without oil can be considered reason - Management Advisor , Sonoma County suitable for use in Christmas tree able choices for use in Douglas fir Cooperative Extension and Statewide IPM plantations.Although the present la - Christmas tree plantations . Both mate - Project ; R.S . Cowles isformer Assistant bel only allows foliar applications to rials show some efficacy against both Entomologist , Department of Entomology , Christmastrees , on most crops it has adelgids and spider mites . However , UC Riverside and current Assistant Ento - been most effectivewhen applied to pyrethroids such as fluvalinate tend to mologist , Connecticut Agricultural Ex - soil for uptake through the roots . select for resistant mite populations periment Station , Valley Laboratory , Con - When protected from the sun , it de - very rapidly , so rotation later in the necticut ; and D.R . Donaldson is County grades slowly so an application results season with other classes of miticides Director , Napa County CooperativeEx - in extended uptake throughout the ( if needed ) should be considered . tension . growing season . For example , the Treatments found unacceptable The authors wish to acknowledge the higher rates labeled for ornamental based on the poor level of control kind cooperation of Big Ranch Christmas landscape trees commonly show insec - were , in order of increasing efficacy : Tree Farm . CALIFORNIA AGRICULTURE , SEPTEMBER - OCTOBER 1996 37