SUPPL. NO.27 SOUTHWESTERN ENTOMOLOGIST DEC.2003

PECAN PRODUCTION IN NORTH AMERICA

BruceW. Wood

USDA-ARS-SEFTNRL, 2l Dunbar Road, Byron, Georgia 31008

ABSTRACT

Fuhre arthropod management strategies forpecan, carya illinoinensls (wangenh.) c.Koch, will likely be increasingly influenced by the cultural sfategies of husbandry protocolsand how they influence the altemate bearing characteristics of Eees and orchards. CommercialNorttr American pecan husbandry involves three distinct generalized commercial productionstategies (i.e., native groves, seedling orchards, and improved orchards), four productionsubsystems (i.e., nonpruned discrete canopies, selectively pruned discrete canopies, hedgepruned discrete canopies, and hedge pruned continuous canopies), and sweral prominent sub-subsystems relating to water (dry vs. inigated), nifrogen (moderate vs. high), ground cover(none vs. grasses vs. legumes vs. inter-cropping), livestock (grazingvs. nongrazing), input(organic vs. non-organic), and pest conhol (biological vs. chemical vs. integratedf. thus,integration of these systems and sub-subsptems yield hundreds of distinct production systerns-each of which potelrtially influences both the natue of arttuopod damage and the economicsuccess of husbandry. The large number of native grove operations, plo, the hend towardindustrialization (i.e., intensivelymanaged improved orchards), low-input management, andorganic famring means that husbandry merits a considerable investrnent in development ofcommercially acceptable arthropod management sEategies. Altemate bearing is a key stessphysiolory phenomenon to which orchard, or grove, profitability is tightly linked; thereforeoccupying a pivotal position on which nearly all commercially

-successful arthropod

management practices are likely to be linked.

INTRODUCTION

P*ag Carya illinoinezsis (Wangenh.) C. Koch, is one of the few economically importantfood crops originating from North America (Flack 1970, wood et al. 1990). It is widelycultivated within its native range and is beginning to be cropped as an exotic tluoughout muchof North America and the world (Wood and Payne l99l). During this time as a horticulturalcrop' pecan has substantially advanced toward biological domestication; however, in the"evolutiona4y'' sense, pecan remains essentially undomesticated. This is because cultivatedcultivars_ are only slightly diverged from wild tlpes; plus they still possess the necessarygenetic fifrress for unaided survival and reproduction in-their naiive habitat (Flack 1970). Asa relatively new horticultural-crop, first receiving serious attention in the early 1900's,husbandry is still evolving and.shategies for artt'o-pod management are also evorving.

Pecan orchards are rong--lived (potentially >rbo years), with genetic diversity beingrelatively low and genetic makeup essentially fixed (aside from mutaiions "nd t *rpt*t, toreplacg $ssing trees). conversglr, the variety and genetic diversity of artlyopoo pests arepotentially great and is rurdergoing continuoui evohitionary change. s"...rri.r husbandrv

therefore involves development of effective and profitable management strategies for amultitude ofever changing co-evolved (>180 species; Payne and Johnson 1979) arthropodpests. Thus, most arthropod pest problems are both complex and dynamic (Hanis l99l). Thismecrs that pecan entomologists face the dilficult task of developing superior pest managementstategies for a continuously wolving pest in a wide variety of production approaches spanningmany different environmental and tree physiological situations.

Hanis (1991) reviewed pecan arthropod management approaches and concluded thatprogress in adapting production methods will benefit from a more integrated holistic approach.He also notes that th€re is need for careful consideration ofeach production situation and thedevelopment of an arttropod management plan consistent with the production program (Ilarris1983, 1985, l99l). The success ofarthropod managem€Nrt shategies is tied to consfraints bycultural practices adopted by horticulturists and farmers. Thus, an understanding of pecanproduction systems, and the relative importance they possess in regards to North Americanproduction, potentially impacts the development of highly successful arthropod pestmanagement strategies. Efforts to develop these strategies are most likely to be successfrrl ifthey take into account key crop associated biological factors, such as alternate bearing, thatdrive cultural strategies devisgd by horticulturists. This report reviews North Americancommercial pecan production systems within which entomologists are tasked with devisingsuccessful arthropod managernent strategies.

PECAN PRODUCTION SYSTEMS

North American Produetion. Commercial nutmeat production within the United Statesoriginates from one offour distinct production regions. These regions are the a) southeast(Virginia Nor& Carolin4 South Carolina G*.ga Florida, Alabam4 Mississippi, Louisian4and Arkansas), b) northem (Tennessee, Kentucky, lndiana, Illinois, Missouri, Iowa, Kansas,and Nebraska), c) south-cental (OHahoma and Texas), and d) westem (New Mexico, Airz'ona,Utatr, Nevad4 and Califomia) (Wood 2001). The majority of production from imp,rovedorchard operations originates from the'southeast regions, followed by the southwestern region.Most ofthe native orchard operations are in the south-cental region and in Louisiana.

The 1997 Agricultural Csnsus indicates that pecan production in the United States iscunently based on about 10,107,170 managed trees (-15% nonbearing), comprising 199,168tla(492,137 acres) (Wood 2001). These orchards and goves are dispersed among 19,900 farmoperationsin24states, androughlyproduceaboutl58,T5Tt(350,000,000lbs)ofin-shellnutsannually. SimilarplantingsinMexicocompriseabout6l,l0Tha(l50,998acres)andproduceabout 54,000 t (120,000,000 lbs) of in-shell nuts @. Herrer4 personal communication). Fifty-six percent of commercial U.S. pecan acreage (199,198 ha) is on farms with 2 40.5 ha (100acres), comprising 5% ofU.S. farms. There are 905 farms managing at least 40 ha (100 acres;i.e.,5.4%o of the total farms) and 124 farms managlng at least202 ha (500 acres; i.e., 0.7Yo ofthe total farms). Thus the vast majority of pecan operations are small, wrth 62% of U.S. pecanfarms managing less than 6.1 ha (15 acres) of trees; although, most of the acreage is associatedwith large farms.

The skewed distribution of the number of pecan farming operations toward smallplanting but concentration ofacreage on relatively few farms possessing large orchards, likelyhas important ramifications for development of optimal pest management strategies. This ispartially because the multitude of small holdings are likely to a) be influenced by bothbeneficials and pests from other crops and forest adjacent to the planting, b) possess lowquality or underpowered spray equipment for arthropod control efforts, c) exhibit great€r cropvulnerability to pests because of lower tree vigor and poorer health, due to less attention tomanagernent of fertilizer and water supplements, and d) be poorly managed from the

standpoint ofpractices that minimize altemate bearing (i.e., most notable that of maintainingmechanical crop thinning and pruning).

The cultivation ofpecan at both errotic and indigenous locations potentially influences thenature ofpecan pest management. For example, exposure of orchards or groves to a broadspecfrum ofwell-adapted co-evolved arthropod pests and beneficials is likely to produce a p€stmanagern€nt situation that could be either more, or possibly less, challenging that an exoticlocation in which an exotic pest or an introduced co-evolved pest outbreak occurs. Manyarthropod pests can be potentially hansported via nuts, propagation wood, or nurs€ry trees toorchard sites outside the host native range to attack ffees; thus, potentially leaving behind co-evolved beneficials that might otherwise suppress pest populations. Additionally, husbandryoutside the native range, can potentially expose trees to exotic pests to which the tree hasinsufficient natural defenses. An example of this is the destructive impact of an indigenousAushalian longhom boter (i.e., Agrianome spinicollis (Macleay)) on hee health and longevityin certain Australian orchards @eane Stahmann, personal communication).

The composition ofpecan fanning units is such that operations tend to be segregated intoone of three ge'neral types of production systems. These are "native", "seedling"n and"improved cultivars" free populations. kr regrds to in-shell production, ,,improved cultivars,,have dominated "nativesn and 'seedlihgs" in the U.S. since about 1970 (Fig. l). Salie,nt aspectsofeach ofthe three generalized production systerns and notable relevance to arthropod pestmanagernent are as follows.

Native Groves. Natives are populations oftrees left standing from forest that have beenappropriately thinned to mar<imize sunlight exposure while also leaving only the bestspecimens. "Bestn is usually based both on the size of the in-shell nut and hee health. Theseselected populations are termed "groves" or "native groves". There are lgGf species ofarthropods that attack pecan frees @ayne and Johnson 1979), and most ofthese can be foundin native groves. The most important of these are listed in Table I and rable 2.

TABLE L Major Arthropod Pests of North American pecan Groves and orchards."

Commonname Scientific name

Pecan weevilBlack pecan aphidPecan nut casebearerHickoryshuckwormPecan leaf scorch miteYellow pecan aphidBlackmargined aphidSouthern green stink bugBrown stink bugDusky stink bugGreen stink bugLeaffooted bug

Curculio caryae (Hom)Melanocallis baryaefoliae @avigAcro b as is nuxvo rel I a NeunzigCydia caryana (Fitch)Eotetranychus hicoriae (McGregor)Monelliops is pecazls @issel)Mo n e I I i a c ary e I I a (F itch)Nezara viridula (Linnaeus)Euschistus serws (Say)Eus c hi s t us tr is t i gmu s (S ay)Acro s t ernum hi I ar e (S ay)Leptoglossus phyllopus (Linnaeus)

" List provided by Ted Cothell

The commercially most important foriar feeding pesrs are usuany aphids [especiallyMonellia caryella (Fitch), Meranocailis caryaefolia" puoi,r1, Mon"uroiri'p"*rs @issel)l

A*,v

Cot -fl(J=!tol-CL

+,=tr

-

o-cot

g

120x103

1 00xl 03

80x{03

60x103

40x103

20x103

0

120x103

100x103

80x103

60x103

40x103

20x103

01920 1940 1960 1980

Year

FIG. l. In-shell production (in metric tons) of "improved cultivars" (A) and "natives andseedling" @) pecan nuts in the United States since 1930.

lmproved Cultivars

B) Natives and Seedlings

and pecan leaf scorch mites, Eotetrancychus hicortae (McGregor)' The most important fruit

pests are usually pecan weevil, Curcalio caryae (Hom), P@il nut casebearer, Acrobasis

nuxyorella Neunzig, and hickory shuckworm, Cydia caryana (Fitch) (Mizzell 2002). Ot

course, other pests can exceed these in eco4omic importance, depending upon the orchard

situation and location.

TABLE 2. Most Common Minor Arthropod Pests of North American Pecan Groves and

Orchards."

Commonname Scientific name

Pecan leafphylloxeraSouthern pecan leaf phylloxeraPecan phylloxeraPecan spittlebugWalnut caterpillarFall webwormPecan cigar casebearerPecan serpentine leafrninerMaybeetlePecan leaf roll miteAlder spittlebugPecan catocalaPecan catocalaPecan budmothShoot curculioShoot curculioNut curculioObscure scalePotato leaftropperAsian ambrosa beetleShothole borer

Phylloxera notabilis (Pergande)P hylloxera nn s e lae (Stoetzel)Phylloxera devastatrix (Pergande)Cl as toptera achatina (Germar)Datana integerima Grote & RobinsonHyp h antr i a cun e a (Dnry)Coleophora laticornella (Clemen$Stigmella j uglandifu liella (Clemens)Phyllophaga spp.Aceria caryae (Kiefer)Cl astop tera o btus e (Say)Catocala maestosa (Huls|Catocala viduata (J. E. Smith)Gret china b o I liana (Slingerland)C o not ra ch e lus p e can a e (Nntt,)C on o t r a c h e lu s a r a tus (G ermar)Conotrachelus hicoriae (Schoot)Chrys omp halus o b s curus (Comstock)Empoascafabae (Haris)Xylo s andrus cras sus culus (Motschulsky)Scolytus rugulosus (Muller)

' List provided by Ted Cottrell

Relevance to Total Production. About 1/3 of the yield of in-shell nuts marketed in theU.S. is from native groves (Thompson 1984, Wood 2001). Although data are unavailable,production from native groves in Mexico is only a small percentage (<5%) of that nation'specan production (A. Bejar, personal communication). In the U.S. industry, production fromnative groves typically comprises most of the crop originating from Oklahoma, l,ouisiana,Kansas, Missowi, and Illinois and much of it from Texas and significant amounts fromArkansas, Mississippi, and Termessee. Because the farm-gate wholesale price received fornatives is usually substantially less than that of improved trees, and because such grovestlpically produce only l/3 to 1/z (typically 560 to ll2Q kgha in-shell nuts) the yield ofimproved orchards, native groves rarely benefit from intense husbandry efforts. Thus, treesare potentially under greater water, nuhitional, or shade stress, plus cost of management inputsbecomes a critically impodant factor in the development of artlnopod management strategiesfor native groves @eid and Eikenberry 1990).

Native groves have long occupied a prominent position in the u.s. pecan industry andwill continue to do so for decades to come. In terms of number of farm operations, there arelikely more farms managing native trees than those of seedling or improved hees.Additionally, the enhanced profit potential for cultivation ofnative-groves, coupled withrelatively low prices for agronomic crops in the 1980's and 1990's, tri teC to a substantialtl:l*. in the acreage of native trees being farmed. This effect is especially prominent inOklahoma where a 26Yo inqease in the number of pecan farms and an 87% increase in thenumber of acres of hees occurred from 1987 until 1997 (Wood 2001). Most of this increasewas due to either native groves being carved frcm riparian forest oi to renewed interest byfarrners in harvesting previously abandoned native groves (M. w. Smith, personalcommunication).

Bclqvance to Arthropgd..Manaeement Strateeies. Native groves naturally possessrelatively high genetic variability and grow on riparian sites characteristic to those in whichthe species evolved. Ofthe three distinct population classes under husbandry, natives aregenetically, and also likely ecologically, most diverse; therefore, most resembling wild pecanpopulations. This population structure, site, and usual close proximity to forest conferssubstantial uniqueness regarding both pest and beneficial arthropod poputations. With theexception ofan occasional individual free, populations ofcertain pists oniy occasionally reachthe destructive levels commonly encountered in seedling o. i-p.o.tr.d orchards. This ispartially due to the relatively minor disruption of the arthropod ecosystem and high geneticdiversity of host trees.

Native groves possess a distinct advantage over seedling or improved orchards, from thestandpoint ofconhol of fruit feeding arthropods, in that they porr"r, key natural defensefactors that tend to be absent, or much reduced, in the seedling oi irnprou"d orchards. Thesefactors are: a) genetic diversity of host genotypes, b) diversity of natural enemies, c) anextreme irregular bearing of individual trees (i.e., high altemate bearing index or trighampttude bearing cycles), and d) synchronized croppingli.e., masting). For-example, pecanwewil populations in native groves are partially checked via periodic irCIting assbciated withsatiation and starvation. Additionally, the genetic diversity olthe host popuiation means thatwhile individual trees may succumb, the grove population is protected from an epidemic@rowning 1980, Harris 1980).

cultural strategies in native groves vary substantially, partly depending upon thegeographical location of the grove and the importance of the grove to tire overatt farminglPlration' Management of groves of pecan is often ancillary to 6ther crops, with cattle oftenbeing the commodity of focus, and thus being allowed to graze among the trees. In fact, manyof these groves primarily function as pasture and shelter for cattlel Such groves typicallysupport native grasses, and improved grasses or legumes. Many ofthese fariring operationsview a1 occasional crop ofpecan nuts as a free gift from nature and thus do relatively tittle inway of management of cultural inputs or pests. conversely, other operations impose a highlevel of management in efforts to maximize grove profitability.

The nature of management received in nativi groves is partially dependent upon thegeographical location, or environment, of the grove. For eiample, groves in Texas aretlpically sprayed with zinc due to the influence ofrelatively high soifp-H on suppression ofroot uptake and soil availability; wh€reas, those in Louisi*u at" ofter, ,p*yrd for pecan scabdue to.the_influence of high hlmidity on susceptibility, and those in ttri nlrthem part of therange in Kansas and Missouri rarely require spraying for either.

Because of the relative low price of nuts from native groves, hees usually receiverelatively little regarding orchard inputs (e.g., irrigation, nutrients, pruning) and are thereforelikely to experience greater physiological stress than tees of the other twJorchard tlpes. Forexample, native trees are usually fairly well fertilized with nitrogen, but they are rarely

6

irrigated. This exposure to dry soil during nut filling, and also dwing the time when trees are

restoring storage pools of photoassimilate and nitrogenous compounds, is likely a key

contributor to severe altemate bearing ofhees in native groves.Altemate bearing is tlryically biennial cycling of flowering and fruit-set, but "on" years

can also occur only every 3-5 years. Large crops ("on") of relatively poor quality nuts are

usually followed by years of little or no flowering and fruit-set ("off') with high nut quality'

Thus stess factors that trigger, or enhance the magnitude of, altemate bearing have pote'lrtialgreat impact on arthropod management strategies. For example, large populations of foliar

f..aing ottnopods, such as aphids and mites, may be a greater threat to quality nutneat yields

aom trighty shessed trees in native groves than to better managed and potentially lower

sfressed trees in seedling or improved orchards.Seedling Orchards. Seedling and improved populations are planted by man and are

termed "orchards" rather than "groves." Seedling fees comprise several subclasses, based on

origin. These subclasses are: a) open-pollinated progeny ofcultivars or favored natives, b) the

rooirtork oftransplanted trees in which the scion died, and c) outdated or archaic cultivars.

Because of usually lower wholesale prices for seedling nuts, seedling orchards typically

receive less cultural and pest management inputs than do improved orchards. They also

tlpically receive greater inputs than do native groves, yet there are notable exceptions.Relevance to Total Production. It is in the southeastern U.S. that seedling orchards are

most prominent (Wood 2001). They decline in both frequency and commercial significance,from east to west, across the U.S. pecan belt. There is little or no nut production originatingfrom seedling orchards west of central Texas. The most prominent states with seedlingorchards are Georgia, Alabama, and Mississippi. There is also substantial production in

Texas, Louisian4 Flodda South Carolina and North Carolina. The total contribution ofseedling derived-nuts to the armual U.S. production ofpecan nuts is usually not as great as that

from native groves, yet they account for a substantial percentage of production in Georgia(-187o), Alabama (fr2%o),Florida (fi2o/r),Mississippi (-4lyl and the Carolinas (^25o/o)'

Relevance to Arthropod Manaeement Strateqies. A usual characteristic of seedlingorchards is that there is substantial variability in nut size and shape characteristics, shellingcharacteristics, nut quality, and time of fruit ripening. Thus, the resulting nut crop is usuallynonrmiform and ofte,n of reduced value, at the wholesale level, than nuts from improvedorchards. This relatively low profitabilify of many seedling orchards means that expenditureson pest management programs are likely to be less than that in either improved orchards orcertain native groves. Additionally, the amount of genetic diversity among trees in seedlingorchards is usually intermediate to that of native or improved orchards. This reducedge,notlpic diversity and reduced economic incentive of state-of-art management often increasethe severity ofproblems attributable to key arthropod pests.

The te1dgncy for less than state-of-art management means that altemate bearing intensityis typically greater in seedling orchards than in improved orchards. For example, the level of"I'

[an index of biermiality ranging from 0-1; where 0 equals no change in production fromyear to year and I reflects an absence ofproduction in alternate years (Pearce and Dobersek-Urbanc 1967)l in Georgia for seedling derived nuts is about 0.34 vs. 0.27 fot nuts fromimproved orchards (Wood 2001). The difference is even more dramatic for Alabama where"l' = 0.64 for seedling nuts and 0.45 for improved nuts.

Improved Orchards. Improved orchards are clonal populations of usually one to tlreecultivars. One of these cultivars typically seryes as the main cultivar and the others aspollinators. Thus, genetic variation among tees is almost always lowest in improved orchards-some of which consist of a single cultivar. These orchards t14ically receive a high level ofcultural and pest management lnputs.

Relevance to Total Productibn. Nuts from improved orchards usually are of greatestoverall value to commerce. The majority of improved orchards in North America includesome combination of the following cultivars: 'stuart', 'Desirable', 'wichita', ,westem Schley',lSchley',

'Pawnee', 'cape Fear' and 'sumner'. About 70% of the nuts produced within theu.S., and about 95% of those in Mexico, originate from improved orchards (wood 2001).within the U.S ., about 40o/o of these originate from Georgr4 2l%o fromTexas, and lgTo fromNew Mexico. Almost all of the production west of central Texas is from improved orchardsand about 72%o of that outside of the native range within the southeastern U.S. is fiomimproved orchards.

Relevance to Arthroood Manaeement Strategies. Production systems associated withimproved orchard operations are highly relevant to pecan pest management strategies. Thisis for the following reasons: a) the vast majority of in-shell pecan production in North Americaoriginates from improved orchards, and this dominance is iitety io substantially increase overtime, b) these orchards are often monoclonal, or nearly so, and thus the near absence ofgeneticdiversity in the host population results in arthropod populations being ofa greater potentialthreat to profitability, c) these orchards usually receive intense cultrual --ugJr*q therefore,the high investrnent in orchard inputs makes it critical that the investneit is substantiallyprotected from arthropod related losses, d) because trees are often managed to maximizecropping, trees are subjected to physiological conditions where foliar damaie by arthropods,o1 damage by other arthropods to ftee organs, can have great impact on both iunent and futpreyields and profits via effects on altemate bearing relaied physiological and Jevelopmentalprocesses (Wood and Reilly 2000), and e) the high level ofnibogen received by these tees canhave significant impact on populations of certJn arthropods and subsequent damage (woodand Reilly 2000).

The "production" related dominance ofimproved orchards and the increasing cost-pricesqueeze felt by all tlpes of pecan farm operations, means that there is pressure on pestTanaggs to devise strategies to reduce conhol costs. Because prophylactic usage ofpesticidesis usually impractical, and because ofthe potential for chemicalsio reduce"canopy photoassimilation (wood and Payne 1984), "ttd th. side-effects of increasing damage due tosuppression of non-target beneficials, there has been considerable pro-gess toward thedevelopment of biorational insecticidal conhol and biological control"stategies. Theimportance ofthe contribution ofbiorationals and biologicali to intensive pecan husbandryis likely to substantially increase.

PRMARY PRODUCTION SUBSYSTEMS

Canopy Management Subsystems. Husbandry strategies in improved orchard operationsare evolving such that there are four distinct cultural strategies dealing with canopymanagement. Each of these confers subtle side-effects on arthropod -*"g*-*t. These fourare orchards with canopies consisting of: a) hedge pruned continuou. "Lopi"r, b) hedgeddlyrete canopies, c) selectively pruneddiscrete .uioii.r, and d) nonpruned oilcrete canopies.Jhey- c{tural sfrategies confer substantial difierences in canopy environment, treephysiological stresses,

Td- r.9p loads; thus, potentially impacti'ng ."rtJn "rtrrropoomanag€ment strategies and the degree ofarthropod related shess trees Jan tolerate.

The increasing economic importance of a stable supply of high q""rity not, uy the NorthA'rnerican pecan industry is a major contributor to cons-idettr. i"'o"ttry "ffi foc,r*ing onthe control of alternate bearing by using either selective limb pruning or hedge pruningstrategies. Such strategies typically increase the amount of foliage per uriit of fruit crop, thusenabling trees to better tolerate certain biotic and abiotic rtr.rrl"..- rrrir ;;"", is alreadybecoming common practice in the southwestem u.S. and is beginnin! to ie"useo in the

southeastern U.S. and Mexico.The hedge-pruning systems are especially relevant to arthropod manageme,nt in that not

only do tees possess a favorable leafarea to fruit ratio, but tree canopies are not as deep andare nearer to the ground. Thus, the nature ofthe spray application equipment, and ability toensure good coverage ofthe canopy, and ability oftrees to tolerate higher populations offoliarpests, potentially has great effect on fufire pest managfirelrt strategies. These effects are bothpositive and negative and merit further investigation. Some potentially negative effects ofthese canopy management trends relate to the potential need for greater attention regardingmanagement of insects attacking tees through cuts on limbs resulting from pruning activities.For exanple, hedged pruned tees in Austalia sufrer considerable damage from an indigenousAustralian longhorn borer (i.e., Agrianome spinicollis), that takes advantage of cuts in largelimbs to colonize trees @eane Statrmarm, personal communication). Additionally, foliardamage by potato leaftroppers, Enpoascafabae (Hanis), greatly increases as the amount andduration ofyoung succulent foliage within the canopy increases due to pruning. Thus, thesemanagement practices can potentially require development of new or better arthropodmanagemeNrt strategies for these pests.

The selective limb pruning discrete canopy system also reduces tree size and opens thecanopy for better penetration ofinsecticidal sprays, but has the side-effect ofleaving behindmajor limbs that have been dehomed. Such practices may prove to produce infection sites forcertain wood-boring pests and may merit research to assess potential threat and to deviseprotective strategies.

The characteristics of North American pecan orchards are likely to change slowly overthe coming decades. This is largely due to the long-lived nature ofpecan trees and orchards,and to the fact that many orchards can be abandoned, or receive minimal orchard management,dwing times of low nut prices and can be returned to intensive management during times ofhigh nut prices. Thus, until recently, orchards or groves were rarely ieplaced. Howwer, thereis now a tend toward orchard renovation in which the least profitable frees are being removedand replaced with new cultivars (Goffet al. 1998).

PRODUCTION TRENDS

There are several production associated trends occurring in the North American pecanindustry. These are partially driven by: a) the fact that pecan is a relatively new crop and isstill being domesticated, b) market forces providing economic incentives to farm€rs able toprovide a stable supply of high quality nuts, and c) the need by many farmers to maximizeproduction and./or profits. Certain of these trends are briefly noted as follows.

Industrialization. The North American pecan industry is slowly evolving towardindustrialization, just as has most other agricultural crops (Wood 2001). There is also agradually increasing "cost-price" squeeze for most pecan farming operations. These two forcesact to increase pressure on farrners to enhance orchard profitability. Thus husbandrypracticesare slowly evolving toward intensive horticultural practices that tend to focus on ma:<imizingprofit per unit ofproduction. Thus, the relative importance ofimproved orchard operations isexpected to substantially outpace that ofseedling orchards or native groves.

If industrialization in pecan evolves according to that of many other fruit and tee nutcrops, then there is the likelihood of increasingly intensive husbandry practices. Thesepractices are likely to be imposed on orchards containing a single main crop cultivar with acouple of interspersed pollinaton. In many cases this monoculture-like system will be locatednear other Carya speoies that share common pests. Thus the ecological events that occurinside orchards will be influenced by plants outside the orchard that support common pests.This situation -superimposed on a monoculhre-like system where nutritive value, extension

of susceptibility windows, etc. - potentially affects host defe,nse mechanisms (i.e., biologicalassociations, confrontation, accommodation, and escapes in time and space; Crtafi 1t77,Hanis 1980) and will likely have great influence on future pest management (Mizzell2002).

Hedge-t1pe pruning shategies are likelyto be central to many future intensive husbandrystrategies. Because hedging greatly increases the amount and duration of shoots and foliagein the elongation phase ofvegetative growth, a key defense mechanism is being altered, andthere is likely to be much more feeding by leaftroppers. This has already been observed inhedge-pruned orchards in Ausfralia and Georgia where feeding damaged foliage can mimiccertain aspects ofZn deficiency @enonal observation). Leaftoppers, especially the glassy-winged sharpshooter, can spread the Xylellafastidiosabacteritmthat is implicated as a keycausal factor in pecan leafscorch disease (Stevenson and Chang 2000, Sanderlin 2001).Development of a particularly virulent strain of this pathogen could create a crisis in amonoculture-like intensively managed hedge-pruned form of pecan husbandry; thus, placinga great deal ofpressure on entomologists to quickly frnd acceptable solutions.. Low Input Management. The profit margin ofmany seedling and improved orchard unitsis little or none. Thus, farmers are beginning to explore the concept of low input management,especially in "off' cropping years. This low input approach involves reductions in fertilization,irrigation, and pest control (diseases, arthropods, and weeds) during the ,,off, year, with theexpectation that profits will be greater when viewed within the context of a biennial timeframe. This approach appears to be far more athactive to farmers cropping pecan in desert-likeregions outside ofthe native range ofpecan than to farm operations in indigenous productionzones possessing a vast aray of co-evolved indigenous pests. This approach appea.s topossess substantial merit in certain orchard situations; hence, there may need to be increasedattention given to refinements in artbropod management strategies and spray thresholds in suchorchards. This exciting aspect ofhusbandry merits further investigation.

The market niche oforganic nuts has recently interested several farmers in developingorchards that meet organic certification requirements. The exclusion of chemical pesticide;from such orchards largely limits serious organic farming to geographical locations outside ofthe native range of pecan" and even then they are likely tobe zuUs,-LiAty distanced from otherpecan operations. The desert climates and wide open spaces ofportions ofwestem Texas,Arizona and New Mexico, and certain areas of Mexico, appear to present opportunities for thisform of husbandry. As market competition stiffens for pecan nuti, it is likeiy ttrat this marketniche will expand. Thus, presenting entomologists with some potentially challengingopportunities that is likely to involve novel approaches to pest management.

Increased Genetic variability. The concept of a polygenetic hosrplant situation inorclards is beginning to attract interest among certain farmers in the southeastem U.S. (Goffet al. 1998)' This approach is intended to take advantage ofthe benefits associated withsubstantial genetic variation, as is tpified by native groves. It involves planting of orchardsutilizing as many improved cultivars as possible that also possess resistanci or toloance to keypests such as pecan scab, black aphids, yellow aphids, and scorch mites. Because there issubstantial cultivar associated variability in the amount of damage by different specificarthropod pests, such as black aphids, there is the possibility that plantings of cultivarspossessing resistance or tolerance might increase profitability due to a reductioriin pest conbolcosts. It appears that a key postulate is that the stategy will slow the adaptation ofiests to thehost genotypes in the orchard, thus extending the potential utility ofpesticides and the needfor sprayng. while the system possesses merit in certain resp"cir, it suffers from a problemcultivars not possessing tmiform ftrit ripening date and nut characteristics. Thus, the approachpossesses serious limitations for industrial level farmers, but may work well for certain small-farm operations.

1 0

Nitrogen Management. Fertilization with nifogen is usually the most expensivenutritional supplonent applied to orchards. Because of its relatively low cost compared tomost other cultural inputs, it tends to be used in excess. Additionally, lack of goodinformation about nitrogen uptake demand periods and movement through the soil profileunder specific orchard situations has likely reduced the effectiveness ofnitrogen added toorchards. The realization by horticulturists that N nutrition probably plays more prominentrole in alternate bearing physiology than previously thought, and the realization that treeslikely need relatively high lateseason levels of nitoge,n for good retum cropping is propellingactivities to enhance late-season nitrogen levels in foliage and in the dormant season storagepool. Such practices potentially influence foliar feeding arthropod populations via thenuhitive qualityof foliage. Thus, the effect of high foliarnihogen levels on foliar feedingpestpopulations merits investigation. Observations by Wood and Reilly (2000) on 'Cheyame'

trees indicated that higher leaf nitrogen reduced damage by the black pecan aphid,Melanocallis caryaefoliae @avis), but increased damage by the pecan leaf scorch mite,Eotetranychus hicoriae (McGregor). Thus, the interactions between higher leaf nitrogen levelsand damage by late-season arthropods could potentially alter pest managementrecommendations.

Zinc Managemenf. Discovery of the ability of foliar applied zinc to correct rosette, andassociated low yields, in the 1930's has led to widespread and multiple applications of zinc toorchards. This practice occurs throughout the pecan-belt and qpically rezults in four to swenapplications per glowing season. The conection ofrosette is considered to be one ofthe keyfactors that have propelled the growth of the North American pecan industry (Sparks 1987).A side-effect ofzinc spray applications is that orchard managers tlpically take advantage ofthe need for application offoliar zinc sprays to also add fungicides and insecticides to thespray mix, thus reducing application costs. However, a disadvantage is that managers oftenadd chernicals to the mix that are not needed and are thus wasting money or inducing pestrelated problerns. Thus tank mixing in association with zinc sprays has been reported to bethe greatest single threat to sound arthropod management (Harris l99l). Foliar zinc sprayshave been noted as being a major barrier to substantially reducing management costs (Hariset al. 1998), This is an q<cellent example where horticulturists can potentially modi$ a keycultural practice for the benefit of IPM.

There are currently research efforts underway to develop better methods ofconhollingzinc deficiency via small amounts of zinc applied to orchard soils. While this is mostpromising for acidic soils, there is a possibility that methods could also be adapted for alkalinesoils. If successful, then this could have a profound effect on pest management in that foliarspraying zinc will no longer offer managers a 'free ride' regarding sprayer operation costs ofapplyng early-season pesticides to canopies. Such a revised cultural practice for zincnutritional contof is likely to cause growers to give greater consideration regarding applicationof insecticides and miticides. Thus, potentially improving the wise usage of pesticides, butalso potentially increasing applicafion costs.

Water Management Most pecan farmers now have a good understanding of the criticalrole that water plap in altemato beaxing physiology and the inlluence on subsequent seasoncropping. This results in the development of water management strategies designed tominimize stress to Eees, especially during the time from kernel.filling until leaf-drop. Theresult is that most improved orchards will be better managed in regards to water status. Thus,these orchards are likely to possess less vulnerability to significant crop damage bypopulations of foliar feeding pests, such as aphids and mites if tree water relations are suchthat tees and orchards experience minimal sfress (Wood and Reilly 2000). Conversely, betterwater relations could potentially extend the window of susceptibility to pests that couldotherwise be avoided, confronted or accommodated (Harris 1991). Thus the increasingly

11

popular practice of irrigation may potentially influence arthropod management strategies,

ARTHROPOD PESTS OF NORTH AMERICAN PECAN PRODUCTION SYSTEMS

There are many co-evolved and a few exotic pests of North American pecan groves andorchards that are potentially influenced by pecan production systems, subsystems, and sub-subsystems. The relatively major arthropod pests are listed in Table 1. While the identity ofthe most important pests varywith orchard location, the most notable pests are usuallypecanweevil, Curculio earyae (Hom); pecan nut casebeuer, Acrobasis nuxvorella Neunzig; blackaphid, Melanocallis caryaefoliae (Davis); hickory shuckworm, Cydia caryana (Fitch); andpecan leaf scorchmite, Eotetrancychus hicoriae (McGregor). However, in certain cases anyof the other pests listed in Table 1 can potentially be the most importarit pest.

The most common relatively minor pests of North American pecan groves and orchardsare noted in Table 2. While this listing is not a comprehensive list of relatively minor pests,it does note many of the most common minor pests. The spittlebugs, caterpillars, scale,curculio, leafrniners, twig girdlers, and root borers can cause severe, but usually spotty damageto trees and orchards.

LINKAGE OF PEST MANAGEMENT STRATEGIES TO ALTERNATE BEARING

An understanding of the nature of the nexus between successful arthropod pestmanagement and alternate bearing is potentially of frrndamental importance if useful pestmanag€ment strategies are to be dweloped for certain arttropod pests. When altemate bearingis synchronized to produce masting, it firnctions in a positive fashion to reduce certain negativeaspects ofpests and also reduce the populations ofcertain arthropods (e.g., pecan weevils)(Chung et al. 1995). However, because most farmers need stable year-to-year income, thepositive effects of altemate bearing and masting are geatly outweighed by the negative effectson nutneat yield and revenue. This need for revenue therefore neutralizes a key naturaldefensive mechanism (i.e., escape in time via masting).

The economically single most important biological problem in pecan husbandry is theinnate nature of the tree to altemately bear crops (Amling et al. 1975). The cropping pattemof individual tees is zuch that relatively large crops are associated with poor nut quality (i.e.,"on" year), whereas, small crops exhibit high nut quality (.off'year). This biennial tendency,a highly predictable and common form of alternate bearing, is especially pronounced incommercial improved-t1pe pecan operations (Gemoets A al. 1976; Wood 1993, 1995) andcauses major revenue and marketing problems, especially if the cyclic amplitude is great.

Alternate Bearing Theory of Pecan. The fundamental physiology of altemate bearing inpecan is largely unknown. However, its study has led to the synthesis of the two salienttheories, the "Carbohydrate Theo{' and the "Phytohormone Theory" (Bamet and Mielke1981), into a new theory -the "Phytohormone-Carbohydrate Theory'' (Wood et al. 2003).This theory is similar to the altemate bearing theories hypothesized for several other tee-fruitcrops (Greene 2000). It purports that flowering, and subsequent cropping, is fundamentallycontrolled at two levels. The first level is the regulatory role of flowering inhibitors andpromoters (produced by developing fruit and foliage) on floral evocation and developmentduring the previous growing season. The second level is the regulatory role on the tree'sdormant season carbohydrate pool on floral development at and soon after bud break ofthesubsequent cropping seuunn. The former Carbohydrate Theory functioned as a "conceptual

tool" on which essentially all husbandry strategies of pecan were linked (Wood 1991). Thus,this Phytohormone-Carbohydrate Theory also possesses merit as a more refined conceptualtool that potentially enables better decision making regarding development or apptcation of

12

either cultural or pest management strategies.Key evidence supporting this Phytohormone-carbohydrate Theory is reported by wood

et al. (2b03). Certain aspects ofpecan fruiting are reviewed as follows: a) retumbloom is

related to date of fruit removal from the tree, with retum flowering being greatest when fruit

are removed early in the season, even substantially before the initiation of kemel filling(worley 1978, Sparks and Brack 1972, wood l9s9); b) the rernoval of fruit during the "late

water stageo (immediately prior to the initiation of kernel filling) of development has anoverwhelming positive impact on retum bloom before there is sigrrificant deposition of kernel

dry weight (wood 1989, Smith and Gallot 1990, Reid et al. 1993); c) water stage fruit contains

high levels of gibberellin-like substances (Wood 1982), a phytohormone known to have apowerful regulatory influence on flowering in other tree species (Greene 2000) [Thus,contributing to the management practice of mechanically reducing crop loads while kemelsexhibit little or no development (Smith and Gallot 1990, Smith et al. 1986, Reid et al. 1993)l;d) shoots, branches, and limbs can be bearing on a cycle opposite to that ofother portions ofthe same tree (Wood 1991); e) there is little or no gross difference in concentration of totalcarbohydrates in one-year-shoots, where flowers are produced for the following crop season(Smith et al. 1986, Wood and McMeans 1982); f) cropping is closely linked to donnant seasonassimilate reserves, especially those in roots (Smith and Waugh 1938; Wood 1989; til/orley

1979a,1979b): g) reductions in canopy health, or longevity, enhances alternate bearing;whereas, long-lived and healthy canopies result in greater retum fruit-set (Worley 1979a'1979b); h) crop-set by certain early ripening cultivars is greater than that of certain lateripening cultivars when crop load is thinned in the previous year (Smith et al. 1986); i) treesand limbs possessing a certain source:sink (leaf:fiuil) equilibrium that exhibits a relatively lowaltemate bearing intensity (Wood l99l); j) there is a high positive correlation between fruit-setand growth of shoots and leaves (Gossard 1933); k) retum bloom is only mildly reduced incrop years following a large nut crop largely devoid ofkemels (Sparks 1974); and l) thataltemate bearing intemity is unrelated to date of fruit ripening or and nut size, but has a stonginverse relationship to duration ofthe post-ripening foliation period, especially in large fruit-size cultivars (Wood et al. 2003). Thus cultural and pest management practices enhancingcanopyhealth and retention usuallyreduce altemate bearing intensity, but do not eliminate thecycling phenomena (Conner and Worley 2000).

Relevance of Arthropod Management to Alternate Bearing. The above mentionedobservations regarding altemate bearing, and implications of the associated Phyohormone-Carbohydrate Theory indicate that tree stress should be minimal if nutmeat yield is to bestabilized at the individual tree level. Thus the potential for impact on altemate bearing is abasic factor by which all cultural or pest management practices must be tested. This is whypecan husbandry strategies tlpically strive for an integrated holistic approach aimed atoptimizing management of biotic and abiotic factors such as water, nutrient elements, light,diseases, and arthropods via minimizing tree stress. Over l8 species ofarthropods have beennoted to utilize pecan leaves for feeding (Ring et al. 1985), thus the influence of foliar feedingarttropods on pecan yields can be sigrificant. Additionally, there are many factors that act tocause fruit loss during the growing season (Harris et al. 1986). One of these is the pecan nutcasebearer. Nut casebearer related fruit abortions is not all bad. For example, in heavy "on"

years fruit production can potentially be beneficial in that they thin an othenvise excessivelylarge crop. In certain cases there might not be a need for insecticidal control of this pest inlarge crop sersons (Hanis et al. 1986). Thus, linkage of arthropod management stategies toalternate bearing can potentially yield direct cost savings as well as help to reduce altematebearing related yield losses.

Unless breeding efforts can break the linkage between altemate bearing andenvironmental sfresses affecting carbohydrate accumulatioq it appean likely tlnt development

1 3

of successful arthropod pest management shategies will need to take into consideralion howthey might contibute to tree stess and affect subsequent cropping. Because ofthe importanceof relatively high inputs of water, light, and nitrogen into most orchard environments, pestmanagement shategies will potentially be influenced by these inputs, Because of theimportanco of canopy photo assimilation capacity to the moderation of alternate bearing,management strategies that substantially reduce assimilation are unlikely to be acceptableunless the cultural strategy can compensate via increased canopy. Because ofthe usually nearstate-of-art management of improved orchards, there is the possibility that native groves andseedling orchards may merit lower pest management spray thresholds than improved orchards.For example, culhral practices employing selective limb pruning or hedge pruning techniquestlpically produce an excess of foliar canopy. Such orchards might therefore potentiallytolerate greater populations of certain foliar feeding arthropods than non-pruned orchards.This possibility merits investigation.

There have been two especially notable examples in which deficiencies in pestmanagement strategies have interacted with altemate bearing physiology to cause majorproblems in husbandry ofimproved orchards. These have been associated with the conhol ofaphids and pecan weevil. In the case of aphids, there are three species ofpecan aphids that canbe especially detrimental to pecan yields under certain circumstances, but are typically onlysecondarypests (i.e., the yellow pecan aphid, blackrnargined aphid, and black pecan aphid areconsidered by most to be the primary aphid pests). It was reported in the mid l9g0,s that oneor more of these aphid species can potentially reduce the photosynthetic activity (Wood et al.1985, Wood and Tedders 1986) and chlorophyll concentation offoliage (Tedders etal. lg82),clog the phloem (Wood et al. 1985), induce reduced photo assimilation due to sooty mold anddust accumulation (wood et al. 1988), remove large amounts of energy via sugars (Teddersand wood 1987, wood et al. 1987), reduce starch levels in shoots (wood and redders l9g2),reduce vegetative growth and plant dryweight (Tedders et al. 1982), and reduce crop yields(Wood et al. 1987). Additionally, it was also reported that most foliar chemical pesticidesbeing used to control aphids were themselves damaging to trees in that they reduced netphoto assimilation by up to about 10-20% for periods up to several days post-heafinent,depending upon the chemical and formulation (Wood and Payne 1984, 1986). Thus, aphidsand their control tools were discovered to confer many negative effects on the physiology andgrowth and developmental processes that were umecogrized. It is also noteworthy that duringthis era it was discovered that in the case of Monellia caryella, population growth waspotentially checked by conditioning by previous feeding, thus potentially influencingsubsequent damage to the hee (Liao and Hanis 1985) and that natwal enemies, especiallyspiders and lacewings, played a key role in reducing aphid populations (Liao et al. 1984).

These aphid related findings coincided with an era in which managers of most seedlingand improved tlpe commercial orchards operated with the mind-set that any damage to thetree's canopy would potentially reduce profits. The new information on potentially harmfulaspects of aphid populations was interpreted by many extension specialists and orchardmanagers to mean that the yellow aphid complex should be kept at very low popularion levelsthroughout the growing season. Chemical pesticides were the weapons of choice, with bothextensive and intensive usage eventually resulting in certain aphid populations rapidlybecoming resistant to pesticides (reducing populations ofbeneficial arthropods that formallyplayed an important role in keeping aphid populations in check) @utcher and Htay 1985).Chemical pesticides were heavily utilized, even though research had indicated that they tooconferred negative effects on canopyphoto assimilation that might, in many cases, be as greatas the negative impact of the aphid population (Wood and Payne 1984, 1986). The result wassomewhat of a catastrophic experience for certain farming operations (especially many ofthose in arid regions), yielding complex problems far exceeding that which they formally

I4

experie,lrced, thus further harming crop yields via the influence of aphids on alternate bearing

physiolory and nut production characteristics. This dark cloud in aphid managernent had a

sitver tining in that it undoubtedly played a key role in convincing orchard managers to

embrace iniegrated pest managernent strategies (Harris 1991) that later resulted in substantial

fiscal savings (Harris et al. 1998). This conversion was also undoubtedly aided by the

"pp.rt*.. -of

tire exotic multicolored Asian ladytird beetle, Harmonia aryridi (Pallas), in

southeastem orchards where this predator greatly reduced damage by yellow-type aphid

populations Qvllrzell 2002).Experiences associated with the control of pecan weevil have also served to encourage

adoption of IPM approaches. It also illustrates the linkage between pest contol and altemate

bearing. Carbaryl proved to be an excellent confol agent for pecan weevi! thus two to three

applications were made to tree cmopies from mid August to mid-late Septerrber whe'n kemel

filling of developing fruit was taking place. Unfortunately, carbaryl was also deadly to manybeneficial artlgopod species in the orchard ecosystem. The loss ofbeneficial populations

typically led to an explosion in the aphid complex and/or an explosion in scorch mites. The

rliult was often severe damage to the foliar canopy at a critical time (i,e., when developingkemels were needing photo assimilates and tree carbohydrate storage pool was unable to be

replenished due to a devastated canopy during the post-ripening period). Thus, misuse ofcarbaryl not only tended to reduce kernel quality in the year ofusage, but also reduced cropsthe following year via the adverse influe,nce of a depleted carbohydrate pool on the amplitudeof altemate bearing. Orchard profrtability plummeted for years afterward due to the entrainingeffect carbaryl had on the biennial bearing cycle. These two above mentioned examples withaphids and pecan weevil illustrate the importance of ensuring that ttre subtle ramifications ofpest contol strategies are taken into consideration before they are recommended to orchardmanag€ni.

The potential direct and indirect negative side-effects ofpesticide spray applications tocanopy photo assimilation rates and zubsequent altemate bearing related yield characteristics,as described above, illustrates a need for the development of control shategies that minimizeexposure of the foliar canopy to chemical pesticides. A search for altematives for aphidcontrol using surfactants or potassium nitrate in air-blast sprays yielded limited success, butat a level below that which is needed in commercial orchard operations (Wood et al. 1995,1997; Wood 1997). Alternatives might include biological agents (e.g., nematodes, fungi,bacteria parasites, and predators), pheromones (e.g., mating disruptors), or application ofchemicals to tnrnks and/or soils. Effective monitoring tools have been developed for mostmajor pecan pests, thus providing a key compone,nt of effective IPM stategies (Mizzell2002).

SI.JMMARY

The development of successful pecan arthropod managem€nt strategies for NorthAmerican pecan operations is challenged with satisffing the needs of many potentially diverseproduction systems. When the generalized commercial production systems (i.e., nativegroves, seedling orchards, and improved orchards) are interfaced with the four orchard canopysubsystems (i.e,, nonplused discrete, selective limb pruned discrete, hedge pruned discrete, andhedge pruned continuous) and a multitude of sub-subsystems (e.g., water, nitrogen, orchardfloor cover, pest managern€nt livestock, polygenetic, and organic), then there are thousandsof distinctly different husbandry systems that potentially merit slightly different approachesto arthropod management. These differences in approach are driven by both economic,biological and ecological constraints. Thus, no single system of arthropod management willlikely accommodate the needs of this diverse array of production situations.

t5

The evolution ofcultural practices toward improving canopy, nitrogen, crop load andwater management, and toward reducing management in "off' years has great potential impacton the efficacy ofcertain arthropod conhol shategies and upon the development offuturestrategies. Thus, future success will be partially linked to the successful integration ofcompatible cultural and arthropod management approaches. The wide variety of productionsystems, plus the continuation of a variety of both large and small changes in husbandrypractices, presents an evolving situation that potentially influences the defense mechanisms(i.e., biological associations, confrontation, accommodation, and escapes in time or space;Hanis 1980) that enable pecan to successfully cope with pest populations. Thus, husbandryevolution in cultural practices, and the cultivars in which they are imposed, potentially affectskey defensive factors (e.g., nutritive quality, tree stress, dtration ofavailability ofsucculentfoliage, altemate bearing, masting, and ripening dates) that present a host of challenges toefforts to develop arthropod management strategies.

The great number of farm operations producing native groves (especially in Texas,Oklahom4 and Louisiana), their longevity, and their profit margins means that there remainsconsiderable need for developing artlnopod confol sfiategies relevant to this quasi-natural lowinput systern. Conversely, the great amount of acreage and production associated withimproved orchard operations indicates that much effort is likely to bejustified regarding thedevelopment of strategies for increasingly intensified cultural systems, many of which reflectsubstantial industrialization.

Pecan afihropod pest management has progressed over the last three decades fromunilateral dependency on chemical pesticides toward greater usage of biologically basedstrategies. Recogrition of the role of pecan fee phpiology, especially that of altemate bearingphysiology, has contributed to this progress. Alternate bearing continues to be a pivotalbiological factor potentially regulating the commercial success of arttropod managementstrategies, especially those for foliar feeding pests. Thus, familiarity with the Phfiohormone-Carbohydrate Theory ofaltemate bearing, and an understanding ofits potential as a conceptualtool, is likely a key factor influencing the commercial success of arthropod managementstrategies by entomologists.

LITERATURECITED

Amling H. J., K. A. Marcus, J. E. Bamett, and N. R. McDaniel. 1975. Nut quality of selectedpecan varieties grown in south Alabama. Auburn University Agr. Expt. Sta. Ctrc.225.

Bamett,J.,andE.A.Mielke. 1981. Altematebearing:are-evaluation. PecanSouth8:20-30.Browning, J. A. 1980. Genetic protective mechanisms of plant-pathogen populations: their

coevolution and use in breeding for resistance, pp. 52-75. In M.K. Hanis [ed.]. Bioloryand Breeding for Resistance to Arthropods and Pathogens in Agricultural Plants. Agric.Comm. Texas A&M Univ. MP-1451.

Chung, C. S., M. K. Harris, and J, B. Storey. 1995. Masting in pecan. J. Amer. Soc. Hort.Sci. 120:386-393.

Conner, P, J., and R. E. Worley. 2000. Altemate bearing intensity of pecan cultivars.HortScience. 35: 1067-1069.

Dutcher, J. D., and T. Htay. 1985. Resurgence and insecticide resistance problems in pecanaphid management, pp. 17-19. In W. W. Neal, W. L. Tedders, and J. D. Dutcher [eds.].Aphids and Phylloxeras ofPecan. Univ. ofGeorgia.

Flack, J. R. 1970. The spread and domestication of the pecan in the United States. PhD Diss.Univ. of Wisconsin, Madison.

Gernoets, E. E., L. A. Gemots, T. E. Cannon, and R. G. Mclrtyre. 1976. Cycles in U. S.pecan production l9l9-1974 identified by power spectral analysis. J. Amer. Soc. Hort.

t 6

Sci . 101:550-553.GoIf, W., M. Nesbitt, R. Mullenax, and F. Raspberry. 1998. Pest resistant cultivars as a way

to reduce input costs. Proc. Southeastern Pecan Growers Assn. 91: 56-64.Gossard, A. C . 1933. The importance of maintaining vigorous terminal growth of pecan

hees. Natl. Pecan Assn. Bull. 32: 84-89.Grant, V. 1977. Organismic evolution. W. H. Freeman and Co., San Francisco.Greene, D. W. 2000. Reducing floral initiation and return bloom in pome fruit trees--

applications and implications. HortTechnololgy I 0: 7 40-7 43.Harris, M. K. 1980. Biology and breeding for resistance to arthropods and pathogens in

agriculturalplants. Agric. Comm. Tex. A&M Univ. MP-1451,Harris, M. K. 1983. Integrated pest management of pecans. Annu. Rev. Entomol. 28:291-

318 .Harris, M. K. 1985. Understanding pecan IPM. Pecan South. 19: 13-21.Harris, M. K. 1991. Pecan arttropod management. pp. 6-15. In B.W. Wood and J. A. Payne

[eds.] . Proc. First Natl. Pecan Wkshp. U.S.D.A., A.R.S., ARS-96.Harris, M. K., B. L. Cutler, and D. R. Ring. 1986. Pecan nut loss from pollination to hawest.

J. Econ. Entomol. 79:1653-1657.Harris, M. K., R. Ree, J. Cooper, J. Jachnaq J. Young, R. Lacewell, and A. Knutson. 1998.

Economic impact ofpecan integrated pest managfirent implementation in Texas. J. Econ.Entomol. 9l : 101 l-1020.

Liao,H., and M. K. Hanis. 1985. Population growth of the blackmargined aphid on pecanin the field. Agric. Ecosystems and Environ. 12: 253-261.

Liao, N., M. K. Harris, F. E. Gilstrap, D. A. Dean, C. W. Ap.ew, G. J. Michels, and F.Mansour. 1984, Natural enemies and other factors affecting seasonal abundance oftheblachnargined aphid on pecan. Southwest. Entomol. 9:404-420.

Mizzell, R.F. 2002. Overview of pecan arthropod pest management. Proc. SoutheasternPecan Growers Assn. 95: 78-87.

Payne, J. A., and W. T. Johnson. 1979. Plant pests. pp. 314-395. ia R. A. Jaynes [ed.]. NutTree Culture in North America. Northern Nut Growers Association, Hamden, Conn.

Pearce, S. C., and S. Dobersek-Urbanc. 1967. The management of irregularity in growth andcropping. J. Hort. Sci.42: 295-305.

Rei4 W., and R. D. Eikenbary. 1990. Developing low-input management strategies for nativepecan orchards. pp. 69-76. .ln B. Wood and J. Payne [eds.]. Pecan Husbandry: Challengesand Opportunities. U.S.D.A., A.R.S., ARS-96, 259 pp.

Reid, W., S. M. Huslikg, M. W. Smith, N. O. Manes, and J. M. Whitworth, 1993. Fruit-removal time influences return bloom of pecan. HortScience 28: 800-802.

Ring, D. R., M. K. Harris, and R. Olsak. 1985. Life tables for pecan leaves in Texas. J. Econ.Entomol. 78: 888-894.

Sanderlin, R. S. 2001. Pecan bacterial leafscorch. The Pecan Grower l3t 4-6.Smith, C. L., and J. G. Waugh. 1938. Growth and fruiting of three varieties of pecans on

different seedling rootstocks. Proc. Amer. Soc, Iiort. Sci. 36: l2l-125.Smith, M. W., and J. C. Gallott. 1990. Mechanical thinning of pecan fruit. Hortscience25'.

414-4t6.Smith, M. W., R. W. McNew, P. L. Ager, and B. C. Cotten. 1986. Seasonal changes in the

carbohydrate concentration in pecan shoots and their relationship to flowering. J. Amer.Soc. Hort. Sci. 111:558-561.

sparks, D. 1974, The altemate fruit bearing problem in pecans. Northem Nut Growers Assn.47: 80-85.

Sparks, D. 1987. Apparent effect of zinc treatment on the growth rate of pecan productionand yield, HortScience 22: 899-9Q1.

I 7

lSparks, D., and C. E. Brack. 1972. Retumbloom and fruit set of pecan from leaf and frgit

removal. HortScience 7: l3l-132.stevenson, K. L., and c. J. chang. 2000. Bacterial leaf scorch -a new disease of pecan? The

Pecan Grower 12: 12.Tedders, W. L., and B, W. Wood. 1987. Field studies of three species of aphids on pecan: an

improved cage for collecting honeydew and glucose-equivalents contained in honeydew.J. Entomol. Sci. 22:23-28.

Tedders, W. L., B. W. Wood, and J. W. Snow. 1982. The effects of ferudngby Monelliopsisnigropunctata, Monellia caryella, and Melanocallis caryaefoliae on tlre growth of pecanseedlings in the greenhouse. J. Econ. Entomol. 75:287-291.

Thompson, T. T. 1984. Pecan cultivars: culrent use and recommendations. Pecan Q. 18: 2G26.

Wood, B. W. 1982. Gibberellinlike substances in developing fiuits of pecan. HortScience17:70-71.

Wood, B. W. 1989. Pecan production responds to root carbohydrates and rootstock. J. Amer.Soc. Hort Sci. l14: 223-228.

Wood,B.W. 1991. Altematebearingofpecan.pp. 180-191. InB.W.WoodandJ.A.Payne[eds.]. Proc. FirstNatl. Pecan Wkshp. U.S.D.A., A.R.S., ARS-96,

Wood, B. W. 1993. Production characteristics of the United States pecan industry. J. Amer.Soc. Hort. Sci. 118:538-545.

Wood, B. W. 1995. Relationship of reproductive and vegetative characteristics of pecan toprevious-season fruit development and post ripening foliation period. J. Amer. Soc. Hort.Sci. 120: 635-642.

Wood, B. W . 1997 . Impact of adjuvants on pecan foliage. HortTechnolo gy 7: 182'184.Woo4 B. W. 2001. Production unit fends and price characteristics within the United States

pecan industry. HortTechnology 11: ll0-118.Wood, B. W., and J. McMeans. 1982. Carbohydrate changes in various organs of bearing and

nonbearing pecan trees. J. Amer. Soc. Hort. Sci. 106: 758-761.Wood, B. W., and J. A. Payne. 1984. Influence of single applications of insecticides on net

photosynthesis of pecan. HortScience 19 : 265 -266.Wood B. W., and J. A. Payne. 1986. Net photosynthesis of orchard grown pecan leaves

reduced by insecticide sprays. HortScience 21 : ll2-ll3 .Wood B. W., and J. A. Payne. 1991. Pecan-an emerging crop. Chronica Horticulhuae 3l: 2l-

23.Wood, B. W., and C. C. Reilly. 2000. Pest damage to pecan is affected by irrigation, niEogen

application, and fruit load. HortScience 35:. 669-671.Wood, B. W., and W. L. Tedders. 1982. Effects of an infestation of blaclrnargined aphid on

carbohydrates in mature Stuart pecan . HortScience 17 : 236-238.Wood, B. W., and W. L. Tedders. 1986. Reduced net photosynthesis of leaves from mahre

pecan hees by three species ofpecan aphids. J. Entomol. Sci. 2l: 355-360.Wood, B. W., P. Conner, and R. Worley. 2003. Relationship of altemate bearing intensity in

pecan to fruit and canopy characteristics. HortScience 38: 361-366.Wood, B. W., J. A. Payne, and L. J. Grauke. 1990. The rise of the U.S. pecan industy.

HortScience 25 : 59 4, 721 -7 23.Wood, B. W., J. A. Payne, and M. T. Smith. 1995. Suppressing pecan aphid populations

using potassium nitrate plus surfactant sprays. HortScience 30: 513-516.Wood, B. W., W. L. Tedders, and J. D. Dutcher. 1987. Energy drain by three pecan aphid

species (Homoptera: Aphididae) and their influence on in-shell pecan production. Environ.Entomol. 16: 1045-1056.

Wood, B. W., W. L. Tedders, and C. C. Reilly. 1988. Sooty mold fungus on pecan foliage

1 8

suppresses light penetration and net photosynthesis. HortScience 23: 851-853.Wood, B. W., W. L. Tedders, and J. Taylor. 1997. Control of pecan aphids with an

organosilicone surfactant. HortScience 32: 107 4-107 6.Wood, B. W., W. L. Tedders, and J. M. Thompson. 1985. Feeding influence of three pecan

aphid species on carbon exchange and phloern integrrty of seedling pecan foliage. J.Amer. Soc. Hort. Sci. ll0:393-397.

Worley, R. E. 1978. Effects of defoliation date on yield quality, nutlet sel and foliageregrowth forpecan. HortScience 6: 446-447.

Worley, R. E. 1979a. Pecan yield, quality, nutlet set and spring growth as a response of timeof fall defoliation. J, Amer. Soc. Hort. Sci. 104: 192-194.

WorleyR. E. 1979b. Fall defoliation date and seasonal carbohydrate concentration of pecanwood tissues. J. Amer. Soc. Hort. Sci. 104: 195-199.

I 9