SOUTHWESTERN ENTOMOLOGIST DEC.2003SUPPL. NO.27

RECENTADVANCESINPECANPESTMANAGEMENTINIMPRoVBDANDSEEDLING PECAN ORCHARDS

Janes D. Dutcher, G' William Hudson and H' C' Ellis

Department of Entomology, University of Georgia

Coliege of Agricultural and Environmental Sciences

TiftonbampuJ, p. O' Box 748, Tifton, Georgia 31793

ABSTRACT

The curent state of pecan insect pest management in improved and seedling

orchards in the southem U.S. is described by a review ofthe recent literature generated by

research and extension p;;;;. New research results are reported on the damage potential

of late season insect pests in pecan orchards from controlled field experiments' Contolling

the shuckmining mjury .u*"i Uy t i.tory shuckworm did not increase pecan yield or kemel

quality during the current ,"".on or, 'Desirable' pecan trees in an infestation that developed

between two and fow weeks after shell-hardening. The combinatiorr of injury by a low

;;"bti"; of blackmargined aphids and_a late season infestation of hickory shuckworm iniDisirable' pecan trees ."u."d " sigrificant degradation in kemel color; whereas, frees

treated with selective chernical conhol of either the aphids or the hickory shuckworm or

both insects had sigrificantly brighter kernel color. Significant linear regression models

were foutd between abundance oi "Oott pecan weevil emergrng from th9 soil beneath tree

crown and number of damaged nuts in the tree. The regression model-s indicated that tre€s

*itrr rrigrro weevil density-emerging beneath the canopy tended to have more damaged

pecans lhan trees with lower weevil density in the soil beneath the canopy'

INTRODUCTION

Insects have a sigrificant impact on production in improved and seedling pecan

(Juglandaceae : Carya illlnoensis $;gh.) K. Koch) orchards in the solthem U. S. and the

itii-y stategy foi contol is integrated pest management (Hanis 1983; Haris et al. 1998;

Layton tSSf; rutcher l99Tb,1997i; EUiJ 2001). Pecan producers are more successtul after

they acquire expertise in insect identification, and knowledge of insect bionomics and

.orrt ol. -

The southem states have effectively trained many pecan producers through

interactive applied research and education progrztms. These growers invest in a high quality

crop with pi&entive herbicide and fungicide applications, comprehensive insect and mite

scouting and management progra.ms, irrigation, plant nutrients applied to the foliage and the

soil, ani sunligtrt manage;ent by thinning and pruning. Seasonal and regional variations in

insect and mite pest populations are high and the grower has to have a comprehensive

scouting program to assess the status of pests. The fruit and foliage is susceptible to insec]

and miie damage for 6 to 7 months and insecticide sprays tlpically control insects for l-2

weeks so that -spray

timing is critical to effective contol. Costs of control have to be

curtailed in many ,"*orrr-drr" to the high year-to-year variability in pegan production'

Forttmately, growers can rely on a large iomplex of be,neficial insects, spiders, mites and

insect diseasJs to keep pest problems in check. Also, good scouting techniques are in place

to determine when a pest outbreak is likely to occur. When an outbreak occurs and a spray

2 l

is required to save the ftiit or foliage the chemical is selected on the basis of its efficacyagainst the pest and its effects on beneficial biological control agents as determined byresgalch at,the experiment station. , we briefly review the currint and emerging IpMtechniques developed by research and extension programs for improved and seedfing-pecano.rch3ds. Then, we present new research results on the damage impact of lri"toryshuckworm, pecan aphids, and pecan weevil on pecan production *d-qr"lity

current Pest Management Techniquei. cunent insect monit#ng and conholtechniques for pecan orchards with improved and seedling trees are a combination ofmonitoring, chemical contol, classical and conservation biol6gical control, and reliance onnatural conhols (Ellis and Bertrand 2001; Dutcher 1997b, l99ic,l99g; Hams and Jaclsnan1996; Mcvay and Hall 1998; Tedders 1983; M. w. Smith et al. l'996a).' tvtonitoring rhe fruitand foliage can often identify_a po-tentially damaging insect popuratioo irr-ii*" t6 apply achemical or biological conhol. After budbreak, itre orctrards ideally are monitored eachweek forfoliage pests' Sampling units for monitoring the tree crown *. tt " "o*pound leaf,the terminal (foliage and stem of the current years stem growth)" and whole crownin:qTd:l. The sample writ is the compound leaf ior measurini trt" t"L"."r occurrence ofaphids-[Homoptera:Aphididae: Monelliopsis pecanis Bissell (yeilow p""* "prrial, Monellia*?:!l! @tch) (blackmargined ryhii), rieranocailis caryiefoh"; @;ri; (bhck pecanThid)J, leafrniners [Lepidoptera:Gracilrariidae: eeuorygictei "oryi"iiiio (chambers),l. !nn?!!!a_JChambers), Corylllt! cgaaefotieila (Clemens); N.pii"ufiO"", Stigmeltajuglandifuliella (clemens); and Heliozelidaeicoptodiica rucrflueila crc.*rr, pecan leafca3eb_earer [!,epidoptera:pyralidae: Acrobasis ju{randis (LaBaron), ;jp;;* leaf scorchmite [Acari:Tetranychidae: Eotetranychus hicoriieMcGregor]. G'or*, llrpicany examinefive compound leaves from every fourth Eee in every rourtf, row ""a ,"ililig rows of eachpecan variety grown on,the farm (Ellis 2001). Seasonal occurrence of insects varies3n;idemlfy among seedling (sown from seed and not grafted to a known cultivar) trees.Each seedling tree has to be considered as a .eparate .variety' and trees are sampleindividually.. Leaf samplestaken- from thgrrinhw of the tree .ro*,. "i rnio-tree heightng th" nut bearing terminals of the hee offer the best indication of insecl ".uuity that willaffect pecan production. predators, parasites and pathogens are monitored by examiningentire leaf terminals (foliage

-on the current yeaxs stem growh, usually three to sevencompound leaves). The scout has a higher probability of firioing p..d;;*itl, this sampleunit as the insects are as likely to inhabit the stem and leaf rachis as the leaf blade.Parasitoids and pathogens.typically attack a portion of the pest population *c *" usuallyless abundant than pests' A larger portion ofihe plant than tLe cornpouna leai is required asa^sample unit to detect populations of these biological control ug."tr, Th; terminal alsooffers a largersample unit than the compound leaifor detecting io* 1r"rr-ii"n one aphid/compormd leaf) populations of black pecan aphids (Drrtcher D:glb). rr.. .ir" of bearingpecan trees (12 years old or older) tlpically ranges g-20 m, and samiles are collected with a!ryru"g pole or from an elevated platforrn oni modified pickup tmck or a hydraulic lift.Infestations of various phylloxerans [Homoptera:phyttoxeidaeiehyiloxera spp includingP, !3vast .ayix Pergande _(gecan phylloxera) and p. notabiris p".g*dr (pecan leafphylloxera)1, spittlebugs [Homoptera:c"r.opid"", Crastoptera o"n"tfi 1o"^ar), andgregarious caterpillars [Lepidoptera:Notodontidae: Dataia ministra Grote A Robinson(yd_ryt caterpillar) and Arctiidae: Hyphantria cunea Drwy (fall webworm)l can be readilyidentified by a whole tree inspection from the ground. control of phylloi#ans requires aninsecticide spray at bud break before the galJappear and the wtroti tree inspection onlyseryes to identifu infestations that can be conholled the following season. Whole tree crowninspection effectively identifies hees during the current season that need to be treated forspittlebugs and gregarious caterpillars, Nut pests are monitored with more sophisticatedsgnlilq techniques. Pecan nut casebearer [Lepidoptera:Py'alidae: Acrobasis ntnvorellaNeunzigl adult flight is monitored with pheromone t aps. bviposition and larval feeding

22

injury ar" monitored by examining fruiting terminals on the tree (Knutson and Ree 1999)'

fi# n"it set to shell-hardening, riut drop is monitored with gravity traps thatcollect nuts as

they fall out of the h* ;ti;A"d nuf clusters @utcher 2002; Hanis et al' 1986)' The

g"'nitv top, keep the ,rot, ttraif,"u" dropped out of the tree from being removed by nut-

[;di;g ioo"ntt aoo -

iirct and nuts damaged by tti:\o-w shuckworm

[Irpidoptera:Tortricidae: Cyaii "o,yo"o(Fitt])1, pecan nut casebearer' hickory nut curculio

iCoi*pi"-,C*"ulionidae:' iorot i"t elus -

hicoriae (Schoof)1, pecan weevil

iC"i""it*",C*"ulionidae: Curculio earyae Qlom)1, spittlebugs: 3nd hemipterans

ti"rriii"*p"rt atomidae: Nezaua viriduta (t.1, nuscniilus seru's (Say), E' tistignus (Say)

and Coreidae: l"prstouri-iipottt^ <Se4r.i;i t' phytlopus (L')l 9an r.eadilv. be identified'

W"*fV otr"*"tiorrif tagg#nut clusters identifies the time that the nut drop occurs'

fmerg*ce of hickory nut litculio and pecan weevil adults is monitored with py:amid traps

ti"J,il"- *a WooO fl9+; beginning iniryly summer and continuing througlr October' The

F"*1t *o developmei oiifr" pJ.*t is also monitored in each variety each week by

ilit"rrrrrg and dissecting u-fe* l.t..t.d pecans from trees. The important phenologic-al

stages of nut development are fruit set, nut expansion, half-shell-hardening, full-shell-

;;?;;; and shuct split. The pecan kemel deveiops through water, gel and dough stages

uno rr,rf""*p*sion and before shuck-split. Pgcg 1ut losses to pecan nut casebearer damage

are most sigrificant betrve." ntit set ;d early fruit expansion as the larva may need to feed

on more than one nrt to "o-ptete its development when the nutlets are small' Before shell-

hardening damage by nut ciuculio, hickory shuckworm, hemipterans, and pecan weevil

."*" tfrJ*t to-rlrop. After shell-hardening, nut curculio does not cause darnage, hickory

shuchrorm mines the ,t urt, -a p"t* *""u-il and hemipterans cause-damage to the kemel'

ih. p"r* t"*el is more susceptille to pecan weevil kernel damage after gel-stage.

New techniques foi monitoring and control have been improved through regional

research. Most recently effective coniol and monitoring systems for pecan.nut casebearer'

stirikbugsandblackpecanaphidshavebeen.developed,fieldleste4andimplemented.incommercial orchards. e trigmv effective monitoring and conhol system was developed for

p..* rrt casebearer Uy coirUining a pheromone rn-onitoring systfir, a sequential sampling

ifur,, ";rrdi.tion model, and inse-cticides (Harril 1995; Ha:ris a al. 1994, 1995a' 1995b,

iSgi; Miff"t et al. 1996j. Important factors in pheromone tap catch were dose, lure age'

and trap design (Knutson et al. 1998). Research has found ways of replacing bry4

5p;9111; insiiciies with tebufenozideiConfirm 2E, Dow AgroSciences,-lndianapolis, IN),

,,'Uiot"tiottA pesticide for pecan nut casebearer control' Pecan nut casebearer monitoring

has been adjisted to predict first nut entry for differe,nt areas ofpecan production (Davis

iSSf; L"yto" 1993; Mulder 1997; Ree 1995). Biological research continues to improve our

*a".tt"iti"g of oviposition and nut entry behavior of pecan nut casebearer (Aguine et al'

iSgii;O tfr" ittto""tion of pecan nut casebearer, pecan weevil and masting of pecan

(Chung et al. 1995; Harris et al. 1996)'' -Hi.tory shuckworm pheromone trap catch with the current lwes is low (Collins et

al. 1995) during the mid-summer even though adults are present and causlq sigrrificant nut

drop (yonce "ira U"V"y l99a) @g. l). Research continues to identiS and evaluate

additional pheromott" "otnpon*is iN{. T. 3mith et al. 1994; M' T. Smith 1995a), trap desigrt

and placement (McVay et ;1. 1995), emergence pattenis and population hends (Mcvay et al'

l99i; yonce and McVay L9g4). ;o-confi;iled field experiments, male moth- response to the

new componenrs was mixed 1iU. 1.. Smitfr 1995a). Analysis of trap catch data indicates

th"t G populations have a clumped distribution that becomes more uniform as the

poputation size increases. These results indicate a need for more traps per orchl{ !o-"rr*t moth flight accurately. The current recommendation is one trap/ten acres (M' T'

Smith 1995a). ntlogical studies have measured the response of hickory-shuckworm la^'ae

and tarvat parasitoids to cold temperatures (Nava-camberos et al. 1996; Yonce et al. 1996)'

23

7o nuts inftsted

i lo t \ t l o ) c r o r \ t

nuts collected per trap

mothg perhap perweek

I

DIto0lo=IIIIII+

!

I

I I

TES=taosEho:'t lt lI I

. l l.ffi

nuts

EHH *3aF -3R g ,a-'3F ";'F g ..uo,

*F F-+gF 3{FF tq9. H

vo

g *"'F

uoo

HH luo.E. ?"S ,ruQ.

c s *G , a Y

; *-q: , \g " %q

collected per trap n v . o o d d t s d t E t-;ry\4o,

*.\, .4

E ? - i 7

{"%

o N r o o B4.

o r i r ( r l c r r c D

TtID{ELatt

IIgo.aE

24

Stink bug monitoring was improved with a new happing technique, where a

pyramidul pecan-weevil nap ivas painteh yellow 11d a large malaise trap was affixed to the

iop lfr,fizefi and Tedders tSgS; Mizel er al. 1997). A pheromone, attractive to brown and

Juskv stint bugs, was discovered and used in pecan orchards to monitor the seasonal

*ti"ity lyonce-anO y,izell 1997). The stink bugs remain in the pecan orchard year around

and are Lw in orchards that maintain a mowed sod with herbicided tree rows. Stink bugs

."or. au."gt in pecan in the fall and anytime whan droughty conditions surround the

orchard arei. Af these times when alternate host plants in adjacent border crops are

harvested or senesce, these areas become less desirable for stink bugs and the stink bugs

migrate into the pecan orchard. The influx of stink bugs from harveste{ peanut fields into

p"i"n t- last 30 days (Mizell et al.1997). Inigated pecan orchards arehighly atfractive to

itint bogr and feeding before shell hardening can cause the nut to abort within 7 days

(Wood and Tedders 1996).Pecan weevil trapping has been improved with pyramidal cone traps (Tedders and

Wood 1994; Tedders eCit. t99q and circle traps (Mulder et al. 1997), and a pheromone

trapping system is in development (Hedin et al. 1996, 1997; Collins et al. 1996)' The

""tiuitiof pecan weevil adults after emergence from the soil is better understood from

recent-res€ruch (Cothell 2001). This research indicates that pecan weevil emergence rate

increases at dusk each day to nearly double the rate during the day, night or dawn. When

weevils emerge, 600/o cr;awl on the ground to the tree trunk and 40% fly to the trunk before

ascending into the tree crown. After ascending into the large (>15-m in heighO trees in this

study, wievils oviposited in a higher p€rcentage of the pecans in the lower third of the

.*opy than in the middle or upper thirds. Weevils were also _easily intercepted with traps

set beiween trees at 5, 8 and 12 i indicating frequent flight of weevils between hees'A sampling technique for black pecan aphid was developed to detect low population

levels and $ve the growers an early waming for each infestation. The sample unit was

changed tom ttre compound leaf to the terminals and complete enumeration of the aphids is

replaced, rating the terminals as having 0, I or 2+ aphids and nymphs are present.

The older r*tpting technique underestimated small populations and overestimated largepopulations. ey noting the presence of adults and/or nymphs a lag period can be identified

between the appearance oi the first adults aphids and exponential population growth

@utcher 1997a).Research has developed pecan pest management progftuns for control of pecan

weevil, hickory shuckworm, pecan nut casebearer and the aphid complex based onintegration ofchemical and biological controls, Alternatives to broad spectrum insecticidesfor lecan pest control were developed. Tebufenozide (Confirm 2F, DowAgrosciences,Indianapolii, IN), for example, effectively controls pecan nut casebearer gregarious

caterpiliars and hickory shuckworm qdthout destroying predacious insects of aphids and

mites (Dutcher 1996). The specific aphidicide, imidacloprid (Provado@ l.6E or Admire@2q,Bayer Chemical Co., Kansas City, MO), effectively controls pecan aphids that tend toincrease rapidly after carbaryl is applied for weevil control during the late season @utcher1994b, Lgrsa, 1996, L997a, 1997b). Pecan weevil conhol is still reliant on sprays ofcarbaryl to the foliage as an adulticide (Tedders and Wood 1995). New biological controlssuch as a rickettsiella-like organism (Adams et al. 1997) may be a potential biologicalcontrol agent against pecan weevil.

Reductions in pecan aphid abundance were often associated with techniques such asintercropping rvith summer crop of sesbania, controlling secondary predation by redimported fire ant and spraying predator attractants that conserved aphidophaga @ugg andDutcher 1993; Kaakeh and Dutcher 1992, 1993c; Dutcher 1993, 1994a, 1995b, 1998).Reductions in the frequency of fungicide sprays were shown to conserve entgmophagousfungi that regulate pecan aphid populations (Pickering et al. 1990). Pecan adhropods wereinfluenced by cool season intercrops (M.W. Smith et al. 1994, 1996a), and methods were

25

developed for screening potential intercrop plants (M.w. smith et al. 1996b). Native pecanproduction was found to be profitable with limited insect control @eid 1993).Organosilicone surfactants were found to control pecan aphids for a short time (Wood et al.1997). Blackmargined aphids and associated honeydew atfracts aphid predaton to the pecanfoliage and may ameliorate biological control of aphids (Ilarris and,Li 1996). Red importedfire ant commonly occurs in pecan orchards and is an important predator of pecan weevil(Dutcher and Sheppard 1981) as well as certain aphidophagous insects (Tedders et al. 1990;Dutcher et al. 1999). The environmental factors effecting pecan aphid population dynamicswere determined (Kaakeh and Dutcher 1993a, 1993b). and the aphids were found to have awide range of tolerance to high temperature and are temporarily reduced by rainfall. Anexcellent resource that integrates and updates information on new biologically orientedmanagement methods for pecan production is the National center for AppropriateTechnology @iver and Ames 2000).

Significant advances have been accomplished in host plant resistance of pecaninsects on pecan cultivars. Resistance of "pawnee" and 'T.Iavajo" cultivars toblackmargined aphid has been demonstrated in greenhouse and field evaluitions (Thompsonand Grauke 1998). These cultivars af,e not immune to aphid infestation, but resistancewould enhance cwrent recommended conhol techniques. These results are consistent witlrlab and field research in Georgia (Kaakeh and Dutcher 1994) where blackmargined, blackpecan and yellow pecan aphids were found to have lower reproductive rates and alteredprobing behavior and lower infestation levels on '?awnee" and "cape Fear" cultivars.Black walnut, buttemut, pecan and several hickory species were invesiigated as potentialsources of resistance factors to aphids (M, T. smith et al. 1993, rra. i. smittr- 1995b),Blackmargined aphid adults lived longer and had higher reproductiv€ rates on pecan, water,scrub, shellbark hickory and hican than on black walnut, butternut, and several otherfickory spp. Percentage survival of blachnargined aphid nynphs to the adult stage waslower on most hickory and walnut species than on pecan, hican or water hickory. iellowpecan aphid adults lived longer and had higher nymph survival on pecan than on hickory orwalnut. Black pecan aphid had similar adult longevity over all bee species but reproducedand developed from nymph to adult only on pecan. pecan cultivars have variablesusceptibility to black pecan aphid feeding damage as measured by the amount of chlorosis.Certain cultivars have a water-soluble antibiotic factor on the leaf surface thar suppressesblack pecan aphid populations (wood and Reilly 1998). Two new cultivars - ..Kanza" and"creek" - have some resistance to hickory shuckworm and "Karza" is highly resistant tophylloxera species (Thompson et al. 1996a,1996b). A leafdisc bioassay was developed toevaluate pecan cultivars for host plant resistance to black pecan aphid (Estes 1995). Pecancultivars differed sigrificantly in susceptibility to hemipteran kernel damage in a recentevaluation over four seasons @utcher et al. 2001). The majority of the cultivars in theexperiment that had consistently low levels of kernel spot also had highly desirablehorticultural characteristics, and these cultivars were recommended for planting. Mostcultivars with consistently high levels of kernel spot were also not recommended forplanting (Worley and Mullinix 1997; Thompson etal. 1996a,1996b).

Research in the area of trap cropping in pecan is a major initiative. Trap croppingeffectively controlled the complex of kemel feeding hemipterans on pecan wittr, consiitent50% reductions in kemel damage with trap crops (M. T. smith 1996,l99g). Differences inthe seasonal occurrence of brown (E. serwn) and dusky (E. tristigmus) stink bugs may beimportant to the effectiveness of trap crops. Brown stink bugs are happed more readily onthe ground than dusky stink bugs that are more abundant in the tree canopy (Cottell et al.2000).

Pecan aphids were found to develop insecticide resistance in the field within twoseasons of the introduction of use of pyrethroids or organophosphates. Combinations ofinsecticides were also losing efficacy over time @utcher 1997d). Black pecan aphids have

26

developed for screening potential intercrop plants (M.W. Smith et al. 1996b). Native pecan

production was found- to be profitable with limited insect control (Reid 1993).

brganosilicone surfactants were found to control pecan aphids for a shorttime (Wood et al.

l9t1. Blackmargined aphids and associated honeydew afbaots aphid predators to the pecan

foliage and may ameliorite biological control of aphids (Hanis and Li 1996). Red importedfire int commonly occrus in pecan orchards and is an important predator of pecan wewil

@utcher and Sheppard 1981) as well as certain aphidophagous insects (Tedders et al' 1990;Dutcher et al. 1999). The environmental factors effecting pecan aphid population dynamicswere determined (Kaakeh and Dutcher 1993a, 1993b), and the aphids were found to have awide range of tolerance to high tenperature and are temporarily reduced by rainfall. Anexcellent resource that integrates and updates information on new biologically orientedmanagement methods for pecan production is the National Center for AppropriateTechnology @iver and Ames 2000).

Significant advances have been accomplished in host plant resistance of pecaninsects on pecan cultivars. Resistance of '?awnee" and 'Navajo" cultivars toblackmargined aphid has been demonstrated in greenhouse and field evaluations (Thompsonand Grauke 1998). These cultivars are not immune to aphid infestation, but resistancewould enhance curaent recommended control techniques. These results are consiste'nt withlab and field research in Georgia (Ikakeh and Dutcher 1994) where blackmargined, blackpecan and yellow pecan aphids were found to have lower reproductive rates and alteredprobing behavior and lower infestation levels on '?awnee" and "Cape Fear" cultivars,Black walnut, buttemut, pecan and several hickory species were investigated as potentialsources of resistance factors to aphids (M. T. Smith et al. 1993, M. T. Smith 1995b).Blackmargined aphid adults lived longer and had higher reproductive rates on pecan, water,scrub, shellbark hickory, and hican than on black walnut, buttemut, and several otherhickory spp. Percentage survival of blachnargined aphid nymphs to the adult stage waslower on most hickory and walnut species than on pecan, hican or water hickory. Yellowpecan aphid adults lived longer and had higher nymph survival on pecan than on hickory orwalnut. Black pecan aphid had similar adult longevity over all tree species but reproducedand developed from nymph to adult only on pecan. Pecan cultivars have variablesusceptibility to black pecan aphid feeding damage as measured by the amount of chlorosis.Certain cultivars have a water-soluble antibiotic factor on the leaf surface that suppressesblack pecan aphid populations (Wood and Reilly 1998). Two new cultivars - "Kanza" and"Creek" - have some resistance to hickory shuckworm and "Kanza" is highly resistant tophylloxera species (Thompson et al. 1996a, 1996b). A leaf disc bioassay was developed toevaluate pecan cultivars for host plant resistance to black pecan aphid (Estes 1995). Pecancultivars differed significantly in susceptibility to hemipteran kernel damage in a recentevaluation over four seasons (Dutcher et al. 2001). The majority of the cultivars in theexperiment that had consistently low levels of kernel spot also had highly desirablehorticultural characteristics, and these cultivars were reconrmended for planting, Mostcultivars with consistently high levels of kernel spot were also not recommended forplanting (Worley and Mullinix 1997; Thompson et aL l996u 1996b).

Research in the area oftrap cropping in pecan is a major initiative. Trap croppingeffectively controlled the complex of kemel feeding hemipterans on pecan with consistent50% reductions in kemel damage with trap crops (M. T. Smith 1996, 1999). Differences inthe seasonal occurrence of brown (E. servus) and dusky (8. tristigmus) stink bugs may beimportant to the effectiveness of trap crops. Brown stink bugs are tapped more readily onthe ground than dusky stink bugs that are more abundant in the free canopy (Cotfrell et al,2000).

Pecan aphids were found to develop insecticide resistance in the field within twoseasons of the introduction of use of pyrethroids or organophosphates. Combinations ofinsecticides were also losing efficacy over time @utcher 1997d). Black pecan aphids have

27

METHODS AND MATERIALS

Pecan nut quality and quantity were compared in insecticide-treated and untreatedpecan tees in two field experiments. The first experiment measured the impact of hickoryshuchrorm infestations on kemel quality and nut yield. The second experiment measuredthe combined effects of hickory shuckworm and blackmargined aphid infestations on kernelquality and nut yield. A third experiment measured the amount of pecan weevil kerneldamage in untreated pecan trees and correlated weevil damage to the number of pecanweevils emerging beneath each tree to the number of pecans damaged in each tree during theseason.

The first experiment was set out in1997 to measure the impact of the time of hickoryshuckworm mining on kernel quality. The experiment was set out in a 4,8-ha block ofpecans planted to the cultivar 'Desirable' in 1986-87. Five untreated pecan trees in theorchard were monitored each week from 6 June to 8 october for nut drop caused by hickoryshuckworm oviosition by collecting dropped pecans from gravity traps and examining themfor oviposition sites. Each gravity trap was a squztre (l.3Xl.3m) net held offthe ground ona plastic frame hung from a scaffold limb on each of the five untreated trees. The trap framewas made from plastic (PVC) inigation pipe (1.3-cm diameter) and the net was made fromarmy surplus, nylon mosquito netting. The frap was positioned below the canopy halfiraybetween the trunk and the dripline. The tap was held in place by a plastic bag filled withsand placed in the center of the net. From 7 August to 8 october, 100 fresh nuts werepicked each week from unteated hees and dissected to determine the percentage withshuchnining damage. Hickory shuckworm moth flight was monitored from 6 June to 8October with pheromone @herocon@ cap code: HSW, Trece Inc., Salinas, CA) baited traps(Pherocon@ IC, Trece Inc., Salinas, CA). Trap catch was recorded every week and lures(one cap p€r trap) were changed every 2 weeks. The treahnents were tlree timing schedulesof late season applications of clpermethrin (Ammo@ 3E, FMC Corp., Philadelphi4 PA) at aconcentration of 0.06 g active ingredient/liter of spray solution. The first freatmsnt was asingle application at shell-hardening on 2l August. The second treatment was a singleapplication at two weeks after shell-hardening on 10 September. The third treafinent wastwo applications at two and four weeks after shell-hardening on l0 September and 24September. All insecticide treaunents were applied with a l,200liter capacity, PTO-driven,airblast, orchard sprayer (Durand-Waylon, LaGrange, GA) at a ground speed of 3.2 km/tr, apump pressure of 5.55 kglcrf , and a spray volume of 25-30-liter per tree depending on thetree size. These treabnents were compared to a fourth treatrnent, an untreated controltreatment for hickory shuckworm infestation level, nut leld and quality. Treatnents wereapplied in a randomized complete block design with three replications per heatment(df*"o*q ur*r, re, m = 3,2,1,17). Each treatment was applied to 12 trees in three, four-treelinear plots, and the center two trees were observed for treafinent effects. Hickoryshuckworm infestation level was measured on 8 October by sampling 50 pecans from eachobservation tree and dissecting the shucks, Shucks with either one or more larvae and/orfeeding sites were counted as infested, and the result was used to calculate the proportion ofthe nut sample infested. Yield of each observation tree was measured directly on 7November by mechanically shaking each tree and collecting nuts from the ground.Percentage of the nut weight in the kemel and nut weight were measured from a 50-nutsample collected from each observation tree after drying the sample in an oven at 55o C for48 hrs. The kemels were then graded as fancy, standard and amber based on color (Worleyand Mullinix 1997). The kemels in each group were weighed and compared to the totalsample weight to determine the percentage of the sample weight in each group. Data weremalyzed for differences between treatrnents with analysis of variance and least sigrificantdifference test (Snedecor and Cochran 1967). Correlation coefficients were calculated

_l28

(Snedocor and Cochran 1967) in tree by tree comparisons over all treatments between

ier.*tug. hickory shuclovorm infestation and nut yield and quafity variables. Summary

statistics- (mean, standard deviation, 95% confidenoe interval) were also calculated

(Snedecor and Cochran 1967) for each variable.The second experiment, in 1998, measured the interaction between aphid feeding

damage and hickory shuckworm shuck mining by connolling neither, each, and both aphids

and shuckworms with selective insecticides. Imidacloprid @rovado@ 1,6E, Bayer Chemical

CO., Kansas City, MO) was applied at a concentration of 20 g active ingredient/liter on 30

August for aphid confol, and spinosad (Success@ 480 SC, Dow AgroSciences,Indianapolis, IN) was applied at a conce,nfation of 0.033 g active ingredient/liter on 30

August and 13 Septernber for hickory shuclororm contol. Treatnents were aranged in acomplete random block desigr (df**'u6"r,*, = 3,4,12) with five single tree replicationsin five blocks with one of the following fieabnents: 1=ro insecticide; 2=spinosad;3=imidacloprid; and 4=spinosad plus imidacloprid. All insecticide treatments were appliedwith a 1,200-liter capacity, PTO-driven, airblast, orchard sprayer @urand-waylon,LaGrange, GA) at a ground speed of 3.2 kmlhr, a pump pressure of 5'55 kg/cm-, and a sprayvolume of 25-30 liter p€r tre€ depending on the fee size. Aphids were monitored on thefoliage of five terminals (current yeafs stsn gowth) per tree each week from 30 August to 6October. Hickory shuckworm infestation level was measured on 6 October. Yield andkemel quality was measured on each tree on 5 November. Data were collected and analysedby the same methods as in the first experiment.

The third erperiment, in 1986, measured the correlation between trap catch andpecan weevil damage in pecan tees that w€re not reated with insecticides. Pecan weeviladult e,mergence wrrs monitored in 33 large 'stuart' pecan fiees in a 1.5'ha plot in PeachCounty, GA, at the U.S.D.A. Southeastem Fnrit and Tree Nut Laboratory. The Eees wereteated with fungicides, herbicides and fertilizer following the recommendations of theGeorgia Cooperative Extension Senrice (Ellis and B€rfrand 1986). The trees w€re notheated for control of pecan weerril for ten seasons prior to the experiment. Adult €merg€Nrcewas monitored from 15 July to l5 Octob€r by placing 12 cone emerg€,nce traps over theweevil infested soil within the drip line of each tree. Traps were 0.96 m in diameter at thebase and 0.96 m in height. Each trap had a closed collection top that only collected weevilsthat emerged directly under the cone trap. Weevils were collected fiom the taps two orthree times per week and adults were sorted by sex and counted. The trees were harvesteddruing Novenrber and Decernber and the total yield, nut and kernel weights, and p€rc€' rtagewewil damage were measured in each bee. Data were analped by conelation andregression analysis and analysis of variance to determine if there were any sigrrificantrelationships between the emergence of weevils and the yield, quality and danrage estimates(Snedecor and Cochran 1967). TVelve closed cone pecan weevil emergence traps w€replaced under the drip line of each tree, during summer and fall of 1986. Four traps were 1.3m, four traps were 2,6 m and four traps were 3.9 m from the tnrnk base. Tbe traps weremonitored from I July to I November on three days per week by collecting and sorting bysex the emerging pecan weevils. The faps only collected weevils that emerged directlybelow the hap (2,89 m'), and each tap covered 0.0000964 ha. At harvest, the yield ofeachtree was measured by shaking the pecans from the tree and onto the ground with amechanical shaker, sweeping the pecans up, putting the pecans through a mechanical cl€an€rthat removed all the trash leaving only the whole pecans, and weighing the pecans. Nutweight and p€rcentage weevil damage was ostimated from a 100-pecan sample that wascollected from each hee (before the pecans were cleaned in the mechanical cleaner), handcleaned, weighed and examined for damage. The number of pecans per fiee was estimatedby measuring number of nuts per kg and multiplying by the yield. The number of damagedpecans wall estimated by multiplying the number of pecans per hee by the proportiondamaged. Yield and nut weight were measured on freshly harvested pecans. Summary

29

statistics (mean, standard deviation, 95% confidence interval) were calculated (Snedecor andCochran 1967) for each variable. Correlation and regression analysis (Snedecor andCochran 1967) were used to deterrrine the sigrificance of relations betrveen the trap catchand the production and damage variables.

RESLILTS

In the first experiment, weekly nut drop and shuck-mining monitoring indicated thathickory shuckworm damaged pecans dropped from the hee between 13 June and 30 Julyand shuck-mining began on 14 August and continued to increase until g october (Fig. lj.The pheromone haps did not collect any moths during the time when shuckworms werecausing nut drop. The freatments of the first experiment resulted in a range of hickoryshuckworm infestation levels that indicated that spraying significantly (p<0.05, ANovA,LSD:3.8%) reduced the percentage infestation (Table 1). The control treatnent had thehighest infestation at 23Yo, the trees receiving one spray at shell-hardening had asignificantly lower infestation at 6.4Yo. The trees receiving either one spray at two weeksafter shell-hardening or two sprays at two and four weeks after shell-hardening hadsignificantly lower infestations at 1.3 and 0.8%, respectively. The reduction in the shuck-mining did not result in a significant (P<0.05, ANOVA) change in the following variables(mean + 95o/o cf): yield (13.6 + 7.7 kdtree), percentage of the nut weight in the kernel (49 +3.2o/o), and whole nut weight (9.1 t 1.8 g/nut). The percentage of the kernel weight in thefancy grade was significantly higher in the trees treated with two sprays than in the controlor the trees treated with one spray. Yield, percentage kernel, percentage fancy grade and nutweight were not significantly conelated to hickory shuckworm infestation in tree-by-treecomparisons overall treatnents.

TABLE l� Effects of the Spray Timing of the Application of Clpermethrin to Pecan Treeson Percent Infestation by Hickory Shuckworm, and the Effects on Kemel euality.

Mean value of indicated response variableoT.eatnent" I

ConholSpray ISpray 2

2 3 a6 .4b1 .3 c

l t bt2bt2b

5 l a5 4 a4 9 a

2 a n d 3 0 . 8 c l 5 a 5 2 aSpray dates correspond to shell-hardening on 2l August (Spray l), and two and four weeks

after shell-hardening (Spray 2 and 3, respectively).o Means in the same column and followed by the same letter are not sigrificantly different(P<0.05, ANOVA, LSD Test).

In the second experiment, hickory shuckworm shuckrnining damage wassigrificantly (P<0.01, F-test, LSD Test) reduced by the spinosad and spinosad plusimidacloprid treatments and not by the control and imidacloprid treatments. Blackrnarginedaphids were the only aphids that were found in the samples and populations were lower thanis usually found in a commercial orchard. These aphids reached a mean peak populationdensity of 15-17 aphidVcompound leaf in the last week of September in trees that were nottreated with imidacloprid, and this was sigrificantly higher @<0.01, ANOVA, LSD = 3.6aphids/compound leafl than blackmargined aphid populations (0.0 aphids/compound leaf) inthe trees treated with imidacloprid on the same sampling date. Blackmargined aphid

30

populations wefe not affected by the spinosad freafinents. There were no sigtificantAff".*"o (P<0.05, ANOVA) between beatn€nts in the percentage kemel or yield' Thepefcentage of the kEmel weight in the fancy grade was significantly lower (P<0.01'IttOVC LSD = 6.8 o/o) in the untreated control than in the spinosad, imidacloprid, andspinosad plus imidacloprid (Table 2.)'

TABLE 2. Interaction of Pest-Specific Insecticides on Hickory Shuclororm andgt*l"tt*g""dAphtdC"ttt"t,K*,"ta d

Mean value of response variablepeak #

Treafinenf Xi"r"rationo brtiavrf y" r*"y' "Zru-"f yt"l@Success + Admire 2b 0 b 13 a 53 a l8 a

l 4 a 0 bAdmireAloneSuccess Alone

1 9 a 5 l a15 a 52a1 b 5 2 a

2 b 1 7 a1 5 a

2 l al 7 a20aControl l6a

"The active ingredient in Success@ @owAgroSciences) is spinosad. The active ingredientin Admire@ (Bayer Chemical Co.) is imidacloprid.b Means in the same column and followed by the same letter are not sigrificantly diff€rent(P<0.01, F-test, Least Significant Differe'nce Test)." Means in the same column and followed by the letter are not significantly different(P<0.05, F-test.).

In the third experiment, pecan weevil perc€ntage kernel damage ranged fiom 21.8 to80.5% with amean (*95% CD of 40,215,0%. The cumulative number of weevils em€rgngin the traps under each t€e ov€r the entire season ranged from 6 to 155 weevilVseason-neewith a mean (t95% CD of 68.4113.9 weevils/season-hee. The wewil denstg was 23,674females/lra, 35A32 malas/ha and 59,106 weevilVha. The cumulative number of fEmaleweevils ernerging in the traps under each tne€ over the entire season ranged from 3 to 68weevildseason-tee with a mean (t95% CD of 27.4t5.8 weevils/season-tree. Thecumulative number of male weevils enrerging in the haps under each tree over the entireseason ranged from 4 to 97 weevils/season-Fee with a mean (*95o/o CD of 41.O18.9weevils/season-hee. The number of damaged pecanVtree ranged from 149 to 7,125 nuts/treewith a mean (85o/o CD of 2,721t647 nuts/tee. Tree by tree analysis foud significantcorrelations (r.ritio,ae1,pq.os = 0.344, and rq;6e"1,61-3t,p4.01 = 0.t142) between the number ofweevils caught per season and the number of nuts damaged (r = 0.4607); the number offernales caught per season per tree and the number of nuts damaged (1 = 0.4123); and, thenumber of males caught per season per tnee and the number of nuts damaged (r = 0.4517).Proportion of the nuts with wewil danage was not related to yield (r = -0.3046). Thesecorelations indicate that the total number of damaged nuts in any given Eee is related to thenumber of weevils emerging beneath the tree and the proportion of the crop with weevildamage is not related to the yield or the number of weevils emerging beneath the tree. Theproportion of the nuts damaged in each tee had the lowest (36.3%) coefficient of variation.Yield (71.3%), number of weevils caught per tee (59.4%) number of females caught perhee (61.6%), number of males caught per f.ee (63,4%o), and number of damaged nuts pertree (69.70/o) had higher coefficients of variation. Significant linear regression models werefound between hap catch and number of damaged nuts (Table 3).

3 1

T4P!E 3. Linear Regression Models of Pecan weevil rrap catch @ependenr variable)and Number of Damaged Nuts (Independent Variable) in a Block of 33 'stuart' Pecan TreesNot Treated for Pecan Weevil in Te,lr Previous Seasons. Byron, Georgia 19g6.

variable# weevils/season# females/season# maleVseason

bo1249.21451.9 "

1370.8 "46.35u32.94b

0.1700"0.2040b

br tr21.53 0.2122

" Significant at the p<0.05 level, t-test or b6 and b1, F-aest for R1o Significant at the p<0.01 level, t-test or be and b1, F-test for R2.

The regression models indicated that trees with higher weevil density emergingbeneath the canopy tended to have more damaged pecans than trees with lower weevildensity in the soil beneath the canopy. The regression equation relating number of femalescaught per tree to number of damaged nuts per hee was not highly significant; whereas, theregression equations relating number of total weevils and males caught per tree to number ofdamaged nuts per tree were both highly significant. Since relative variation is equal for allvariables, one remotely possible reason for the higher probability that males are i predictorof damage is that males may play a role in the location and nuts and attraction of fe,males tothe nuts.

DISCUSSION

Effective decision tools for applyrng insect controls rely on understanding therelationship between pest abundance and damage impact. The size of pecan trees and thevariable nature ofinsect pest abundance between seasons and orchards make it difficult toisolate the damage of a particular insect pest and measure its impact on yield or quality.Another confounding factor is the high variability between years in pecan nut yield. Mostpecan insect pests are indigenous to hickory and pecan and the qualitative consequences of alack of insect control are the damage cawed by feeding and the reinfestation of the orchard.These factors contribute to the low number of research papers that quantifr the damageimpact of pecan pests. Foliage feeding insects have an accumulative and additivedehimental effect on pecan nut quality and production. Aphids extract a large amount ofenergy from the pecan tree (wood and redders 1985), and poor or even moderately goodaphid conhol has been shown to result in a significant and progressively worseningreduction in the trees' ability to produce pistillate flowers and a crop in subsequent seasons(Dutcher et al. 1984, Dutcher 1985). Interactions between leafnitogen concentration, leafwater status or crop load and feeding damage by black pecan aphids and mites produce sideeffects. Improving leaf N and leaf water status and a lower crop load reduced black pecanaphid damage; whereas, improving leaf N and leaf water status made pecan leaf scorch mitedarnage more severe (Wood and Reilly 2000). Nut feeding insects cause a direct reductionin pecan production and quality. Gall formation by P. devastatrix in the spring on the pecanstems and nut clusters reduces nut cluster size and nut weight of affected terminals at harvest(Neel and Hedin 1985). Pecan nut casebearer losses in the spring are carried through toharvest in the fall (Dutcher 2002). Nut drop caused by insects is far less than nut dropcaused by natural abortion of nuts by the tree @utcher 2002,Haris et al. 1986). At harvestin a commercial orchard, typically 20o/o of the nuts have shriveled kernels and are blownover the mechanical hawester or are rejected on the conveyer belt due to cracked shells orpecan weevil emergence holes (Eikenbary et al. 1983). Pecan weevil damage can be

32

significant even when chemical controls are applied (Hall et al. 1981, Hall and Eikenbary1983). Ow results indicate that control of hickory shuckworm infestations can increasekemel color slightly if ilrey are contolled late in the season during the current season. Wheninfestations of trickory shuckworm and blackmargined aphid are low, the combined effect ofboth insects was associated with a highly significant reduction in kemel color. Thereductions in kernel color by either aphids alone or hickory shuclnrorm alone was notsigrrificant. Our results also show that pecan wewil kemel damage is related to trap catch ofadults ernerging from the soil beneath the tree. Pecan weevil can cause a direct loss ofup to80% of the kemels. Lack of control of pecan weevil, hickory shuckworm andblackmargined aphid also contributes to the reinfestation of the orchards during thefollowing season since all three pests complete their life cycles in the pecan orchard.

ACKNOWLEDGMENT

The research was supported by funds provided by the Georgia CommodityCommission for Pecans, the University of Georgia College of Agricultural andEnvironmental Sciences. Dr. J. A. Payne and Ms. Ann Amis of the U.S.D.A. SoutheasternFruit and Tree Nut Research Laboratory provided support and the orchard for the thirdexperiment. Griffin Chemical Co., Dow AgroSciences, and FMC Corp. providedinsecticides and funding for the research.

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