Western tentiform leafminer populations can vary tremendously between years or even between generations within a single year. Increasing resistance to organophosphate insecticides and variable effectiveness of at least six parasitic wasp species that attack the leafminer can influence the population size

Alston, Diane G.

Reding, Michael E.

English

DigitalCommons@USU

ItuhStuteUNIVERSITYEXTENSIONOrchard IPM Series HG/Orchard/04Western lentiform LeafminerPhyllonorycter elmaellaby Diane G. Alston and Michael E. RedingDo You Know?• Western tentiform leafminer is an indirect pestthat mines the leaves of apple and cherry.• It can diminish the photosynthetic capability oftrees and reduce fruit size and quality.• Leafminer populations can fluctuate dramaticallywithin and between years.• Biological control by numerous, naturallyoccurring wasps is common.• Successful management requires a good samplingprogram and knowledge of treatment thresholds:I mine per leaf in early June2 mines per leaf in mid-June to July5 mines per leaf in August• Numbers of mines on leaves should be sampledfrom June through August.• Leafminers are resistant to Illany commoninsecticides.• Insecticides have a detrimental effect on their naturalbiological control agents-parasitic wasps.Western tentiform leafminer populations can varytremendously between years or even betweengenerations within a single year. Increasing resistance toorganophosphate insecticides and variable effectivenessof at least six parasitic wasp species that attack theleafminer can influence the population size.In Utah, the leafminer typically has three generationsper year but may have as many as four in some years. Theimmature larval stages-sap feeders and tissue feeders-feed on apple and cherry leaves. When densities are highenough, feeding can cause a reduction in fruit size andquality.Underside ofapple leaf showing mines of the western tentiform leafminer.Sap-feeding larva inside mine.Adult moths are tiny ('/8-'/5 inch long), and can be found restingon leaves and flying in the orchard.Hosts----------applecherrypearpruneWestern Tentiform Leafminer Life HistoryThe two arrows indicate when sap-feeding larvae should bemonitored during the second and third generations, because ifcontrol treatments are necessary they should target this stage.insecticide ResistanceInsecticidesChemical control is most effective against sapfeeding larvae inmines and adult moths flying in orchards. Insecticide sprays shouldonly be applied when leafminertreatment thresholds are exceededduring the second or third generation (see above). Pre-bloomapplications targeting first generation sapfeeders are onlyrecommended if large numbers of adult moths are observed in theorchard during April or May, or egg counts exceed three pel' leafduring tight cluster to pink stage of apple.The recommended insecticide is:.. oxamyl (Vydate)-controls adults and sapfeedersWestern tentiform Jeafminer has developed resistance tonumerous organophosphate and organochlorine insecticidescommonly used in orchards over the past 40 years. Oxamyl(Vydate) still appears to be an effective chemical but should only beused when necessary because it disrupts biological control ofleafminers and other orchard pests.Insecticides to A voidInsecticides that are toxic to the parasites should be avoidedduring mid- to late summer if possible. In Washington studies, thefollowing insecticides were shown to have moderate to high toxicityto Pnigalioflavipes, the main parasite of western tentiformleafminerin the Northwest:4- cncapsulated methyl parathion (Penncap)<$> chlorpyrifos (Lorsban)-$- esfenvalerate (Asana)+ endosulfan (Thiodan).. oxamyl (Vydate)Conservation of parasites is important to a good biologicalcontrol program and can reduce the need for insecticidc control.Utah State University Extension, an equal opportunity employer, providesprogl'<ll1lS and scrvices to all pcrsons regardlcss of race. age, gender, color,religion, national origin or disability. Issued in furtherance of CooperativeExtension work, Acts of May 8 lind June 30, 1914, in cooperation with the U.S.Depllftlllent of Agriculture, Robert L. Gillilllnd, Vice President and Director,Cooperative Extension Service. Utah State University.Parasitized Le(ifminerTo determine if a leafminer larva has been parasitized, opcn upa mine and look for one of the following:'*' A wasp larva feeding on a deflated leafminer larva+ The pupal stage of the wasp along with a shriveledleafmincr larva.. An empty mine with the remains of a leafminer larva and awasp pupal case and no emergence tube formed by the adultleafminer mothIn the last case, the adult wasp has already emerged from itspupa and exited through a smaller hole, which is difficult to observe.Biological ControlThere arc at least six species of exoparasitic wasps that allack!cafminers in the Northwest, and their presence in Utah orchards iscommon. Leafminer parasitism can be as high as 90% and caneliminate the need for chemical control ofeven a formerly highpopulation. The wasps lay their eggs inside the mines on the outsideof leafminer larvae. Wasp larvae hatch from the eggs and feed ondeveloping leafminer larvae from the outside.Return in 5-7 days to doanother quick evaluation.Take a complete sample (see below).Sampling should continue throughAugust.I or more mines per leaf and parasitismof larvae is less than 30%"2 or more mines per leaf and parasitismof larvae is less than 30%"5 or more active mines per leaf'Treatment Threshold1/2-1 mine per leafSampling ThresholdSecond Generation: Mid-June To Early JulyIf terminals have:< 1/2 mine per leafThirdAugustMid-June to JulyManagemInsecticides targeted for leafminer control are most effectiveagainst the sap feeder stage although parasitism is not usuallyevident until the tissue feeder stage. Therefore, parasite levels fromearlier generations should be considered along with currentsapfceder mine densities during second and third generations todetermine if treatment thresholds have been reached.Complete Sampling MethodScouting for western tentiform leafminer can be done at thesame time as mite sampling (see "Web Spinning Spider Mite"bulletin). If you have a large acreage of apples and cherries, you maywant to select several representative blocks where you wiJl conductthe scouting program. Randomly select J0 trees scattered throughouta 2- to 5-acre block to sample. If the orchard block is larger than 5acres, it may be necessary to sample more trees.How to Sample.. If the quick evaluation method indicates the need for acomplete sample, sample for second generation leafminersduring mid-June and early July.+ Scout designated orchard blocks every 1-2 weeks.+- On each sampling date, collect 10 leaves from each of the 10trees (100 leaves total).• Count the number of mines that you find and determine theaverage number of mines per leaf for the orchard block.(Divide the total number of mines by 100. See WesternTentiform Leafminer Sampling Form.)+ These same leaves can be used to monitor for mites.$- Third generation leafminers should be sampled in early to mid-August using the quick evaluation or complete method asindicated by the density of the mines present.4- If the second generation was treated or if sap feeders do 110tappear until late August or September, then it is not necessaryto sample the third generation.°Ireatment Thresholds"Open up a subsamplc of mines to look for parasites (see descriptionbelow).hTo determine if mine no longer contains an active larva, look formpresence of adult emergence tube attached to mine all lower leafsurface.Leafminer GenerationSecondEarly JuneLarvae feeding on leaves can:%, Reduce photosynthetic capability of leaves.-;p Disrupt the growth regulating and ripening processesgoverned by hormones produced in the leaves{o Affect fruit quality by slowing sugar development9'> Cause leaf drop, premature ripening, and fruit drop in severeinfestations1b Increase susceptibility to chemical burn in heavily infestedleaves{."C Increase fruit sunburn if leaves surrounding fruit are curled orhave fallen prematurelySampling should focus on the number of mines in leaves. Thebest time to sample for western tentiform leafminer larvae is at thebeginning of the second generation, which usually occurs from mid-June to early July. SampJing earlier in the season for first generationeggs and sap feeder larvae is possible, but the eggs arc difficult tolocate and identify, and there is a poor relationship between thenumber of first generation eggs and the resulting mines.Quick Evaluation MethodHow to Sample.. Begin sampling in mid-June.~ Walk through the orchard and quickly scan tree terminals (leafclusters at the ends of shoots) to estimate the number of minesper leaf... Sap feeders arc the predominant stage at this time, so look onthe undersides of leaves for mines.Timing ControLSap Feeder.. Instal's 1-3<$- Size and color: 1/12 inch long by the third instal',cream in color~ Shape: flat, wedge-shaped, and legless'1& Where: feeds on sap from the spongy mesophyll layer ofleaves with sucking mouthparts• Separates outer layer of the leaf undersurface from the tissueabove to form a mine, which often follows leaf veins+ Mines appear as a blotch and are only visible from theundersides of leaves at this stageTissue Feeder.. Instal's 4-5., Size and color: I/S to 1/6 inch long, cream turning yellow bythe fifth instar.. Shape: cylindrical with legs, round head, and chewingmouthparts+ Where: feeds on leaf tissue just up to, but not through, theepidennis4> Attaches silken threads to both sides of the mine pulling themtogether to form a tent-like structure in the leaf4> Mines can be seen from the upper leaf surfaces and have acharacteristic mottled appearance with white spots on topwhere green tissue has been removed.. Fifth instal' larvae spin a silken chamber for pupating insidethemine++larva-Damaging Stage.. Newly hatched larva mines down through egg caseinto leaf tissuePasses through five instal's~ Size: l/S to lis inch long, small, slender moth+ Color: forewings with golden brown and white bands edgedwith black; hindwings are gray with long hairs on the edges-$ Shape: wings are held roof-like over the body when at rest.. When: first generation moths emerge from overwinteringpupae in the early spring often around the green tip stageof apple$ May be up to three additional flights in the summer and fall;adult moths emerge continuously from June throughSeptember.. Life stages begin to dverlap after the first generation+ Females lay eggs shortly after emergingEgg+ Size: extremely small, about 1/100 to 1180 inch in diameter anddifficult to see without magnificationColor and shape: transparent when first laid turningyellowish green; round and flatWhere; on the undersides of leavesHatches in 1-2 weekslife Hi§tory__~_~_Pupa-Overwintering Stage... Size: 1/8 to l/S inch long.. Color: yellow-brown changing to dark brown just before theadult emerges.. Shape: cylindrical tapering sharply at the rear end.. Where: Qvcrwintcrillgpupac arc inside mines in fallen leaves;summer pupae arc inside mines in leaves 011 trees... Summer pupation lasts 7-10 days'$> Just before emerging, pupae cut through mine and protrude outthe lower leaf surface.. Pupal skins remain attached to the mine after adults emergeand are called "emergence tubes"AdultWestern lentiform Leafminer Sampling Form-Apple and CherryComplete Sampling Method for Second and Third Generations(Mid-June to August)Orchard Block Scout _Number of Mines Per LeafDate _Leaf 1 Leaf 2 Leaf 3 Leaf 4 Leaf 5 Leaf 6 Leaf 7 Leaf 8 Leaf 9 Leaf 10 Tree TotalTree 1Tree 2Tree 3Tree 4------Tree 5-Tree 6-_._---Tree 7---Tree 8""""---_._--Tree 9Tree 10Total number of mines for 10 trees--Average number of mines per leaffor 10 trees (divide above slim by 100) per leafInstructionsI. Every 1-2 weeks, choose one or several representative orchard blocks for sampling.2. Randomly select 10 trees scattered throughout a 2- to 5-acre block. If orchard is larger than .'5 acres, it may benecessary to sample more trees.3. On each sampling c1ate, collect 10 leaves from each of the 10 trees (100 leaves total). These same leaves can be usedto monitor for mites (refer to mite sampling form).4. Count the number of mines and determine the average number of mines per leaf for each orchard block (to find theaverage, divide the total number of mines by 100).5. If leaf mine counts are high, record counts from every leaf. Otherwise, record only total mine counts from all 10leaves for each tree.n'eatment Thl'esholds*Second GenerationEarly June-one or more mines per leaf and parasitism less than 30%Mid-June to July-two or more mines per leaf and parasitismless than 30%Third GenerationAugust-five or more active mines per leaf*See manual for more complete information

Western Tentiform Leafminer

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Western Tentiform Leafminer

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