Tree nd Forestry Science nd Biotechnology 29 Glol Science Books Citrus Tree Aiotic nd Biotic Stress nd Impliction of Simultion nd Modeling Tools in Tree Mngement Hong Li * Nov Scoti Agriculturl College, Deprtment of Plnt nd Animl Sciences, Truro, P.O. Box 55, NS, B2N 5E3, Cnd Correspondence: * hli@nsc.c ABSTRACT Plnt iotic nd iotic stress is relted to unfvorle nd environmentl constrints. As wrm climte tree fruit crop, citrus (Citrus sinensis (L.) Os.) is dpted to wide vriety of soil types nd growth conditions. However, when wterlogging, soil cidity nd root weevil infesttion occur simultneously, citrus roots cn e injured from neroic disturnce, oxygen deprivtion nd root injury, which cn led to tree decline. Multi-yer sptil overly ptterns of plnts, insects nd soils my yield mngement insights for reducing plnt iotic nd iotic stresses. This pper ttempts to summrize iotic nd iotic stress of citrus trees ssocited with soil neroe, soil wterlogging, environmentl cidity nd Diprepes revitus root weevil infesttion, nd to give n overview of the development of new iologicl tools such s greenhouse simultion nd model prediction tools for integrted fruit production of citrus. Greenhouse simultion studies nd series of multi-yer studies t citrus orchrd scle hve een conducted cross center nd southern counties in Florid. The results showed tht citrus tree decline ws correlted with neroe nd high soil Fe concentrtions (P <.5), nd citrus tree iotic nd iotic stress is directly reflected y low lef stomtl conductnce, flooding root dmge, weevil lrvl root feeding injury, nd neroic-relted soil redox potentil. Citrus rootstock roots were injured up to three weeks of sumergence nd flooded-roots were more susceptile to Diprepes root weevil feeding thn non-flooded roots. Time series nlysis revels tht root dult weevil popultion outreks were ssocited with wrm ir tempertures cross period of three yers (r =.49, P <.67), suggesting tht wrming conditions would contriute to more tree iotic stress. Greenhouse simultion tools nd time series forecst models hve the impliction in reducing iotic nd iotic stress of citrus trees. Keywords: citrus root injury, citrus rootstocks, citrus root weevil, insect-environmentl reltions, lrvl survivl, lef stomtl conductnce, soil oxidtion-reduction potentil, time series nlysis CONTENTS INTRODUCTION... 66 Biology of citrus root weevil Diprepes revitus (L.)... 67 Synthesis of citrus tree iotic nd iotic stress... 67 Reducing citrus tree iotic nd iotic stress... 67 CITRUS TREE DECLINE UNDER ANAEROBE, HIGH SOIL IRON AND ROOT WEEVIL FEEDING... 68 CITRUS TREE ABIOTIC STRESS FROM POOR SOIL REDOX POTENTIAL AND LEAF STOMATAL CONDUCTANCE... 7 CITRUS TREE TOLERANCE TO LARVAL FEEDING AND ROOT WEEVIL LARVAL SURVIVAL... 73 IMPLICATION OF TIME SERIES MODEL IN ROOT WEEVIL CONTROL FOR REDUCING CITRUS BIOTIC STRESS... 73 CONCLUSIONS... 77 ACKNOWLEDGEMENTS... 77 REFERENCES... 77 INTRODUCTION Plnt stress is the stte of plnt under the conditions of force pplied nd dmge is the result of too high tress tht cn no longer e compensted for (Lichenthler 1996; Gutschick 1999; Bry et l. 2; Mittler 26; Lughlin nd Aell 27). Plnt stress is defined s n externl fctor tht exerts disdvntgeous influence on plnt, nd the concept of stress is intimtely ssocited with tht of stress tolernce tht is the plnt s fitness to cope n unfvorle environment nd n ttck (Tiz nd Zeiger 22; Mittler 26; Li et l. 28). Aiotic nd iotic stress conditions my result in extensive loss in citrus production (Olsen et l. 2; Fernndez-Bllester et l. 23; Li et l. 26; Syvertsen nd Hnlin 28). Most stresses fced y plnts re either iotic (e.g. neroe, flooding, cidity, slinity, het, drought, or nutrient deficits) or iotic (e.g. insect, disese or pthogen), which re relted to environmentl conditions (White 1984; Mttson nd Hck 1987; Dorn et l. 1999; Li et l. 23, 23; Rmirez-Rodriguez 25; Grrett et l. 26; Li et l. 26, 28). Plnts show some degree of stress when exposed to unfvorle environments nd these stresses cn collectively contriute to ffect plnt growth nd crop productivity (Blum 1996; Tiz nd Zeiger 22; Jones et l. 23; Li et l. 23, 25, 26, 27). It is estimted tht up to 82% of potentil crop yields re lost due to iotic stress nnully (Bry et l. 2). In North Americ, citrus production totls 14.9 illion kilogrms, representing 18% of world totl production. Florid produces 82% of totl citrus production in North Americ. Citrus, wrm climte fruit tree in the Rutcee fmily, performs est in sutropicl climtes, where there is slight chnge of seson ut little or no chnce of freezing wether. Received: 26 August, 28. Accepted: 14 Octoer, 28. Invited Review
Tree nd Forestry Science nd Biotechnology 3 (Specil Issue 1), 66-78 29 Glol Science Books Citrus is dpted to wide rnge of soil types nd is more tolernt of high or low ph. Citrus trees re grown on lmost pure snd in centrl Florid, to orgnic muck ner the Evergldes, to lomy, hevy, high-ph soils in the Sn Joquin Vlley of Cliforni (Rieger 25). Citrus fruits otin their highest internl qulity (juice content, sugr nd cid levels) in Florid sutropicl humid climtes, while irrigted citrus fruits chieve est externl qulity in Cliforni Mediterrnen climte (Rieger 25). However, citrus species re susceptile to numer of disese nd insect infesttion (Olsen et l. 2) nd citrus trees generlly do not tolerte soil flooding for more thn few dys without injury (Rieger 25). Temperture nd soil wter re the min environmentl fctors controlling citrus tree helth nd qulity (Flivene et l. 26; Syvertsen nd Hnlon 28). Florid citrus soils rnge from welldrined Entisols on reltively high, rolling lndscpes to poorly-drined Alfisoils nd Spodosols on low-lying fltwoods (Orez nd Collins 22). Most fltwoods soils contin high levels of ctive hydrogen ecuse of high rinfll, luminum from soil recting with wter to give free hydrogen (Li et l. 27). Biology of citrus root weevil Diprepes revitus (L.) The root weevil, Diprepes revitus (L.) (Coleopter: Curculionide), originlly from the Crien, hs ecome mjor pest of citrus nd other griculturl crops in Florid in recent yers (Nigg et l. 21; Futch 23; Grhm et l. 23; McCoy et l. 23; Nigg et l. 23; Sturt et l. 24). Diprepes root weevil dults re citrus lef feeders of ll tree vrieties nd femles deposit eggs in msses glued etween leves in the citrus cnopy. Htching neontes fll to the soil surfce, nd move into the soil where they feed on roots nd susequently pupte (Nigg et l. 21; McCoy et l. 23). Diprepes lrvl growth is consistently fst t mient temperture of 22-26 C (Lpointe 2). Growth of Diprepes lrve could e n increse of 36-375 times of their weights s 1-dy-old neontes within 3 dys of infesttion, nd 24-37 times within 4 dys of infesttion on citrus roots in room temperture in the greenhouse (Li et l. 23, 26, 27). The time for single genertion from Diprepes oviposition to dult emergence is estimted to e out 22 weeks (or 15 dys) t 26 C under the lortory conditions (Lpointe 2). Diprepes root weevil dults might e ttrctive to locl trees where their emerging sites re in citrus orchrds s the weevils move reltively little (Nigg et l. 23). In citrus orchrd in centrl Florid, totl of 619 dult weevils were cptured nd then 58 dults were mrked nd relesed. Over period of 1 weeks of relese, 146 weevils (or 25% of the relesed weevils) were re-cptured (Nigg et l. 23). It ws reported tht 4% of recptured mrked dult weevils moved within -24 m, 41% of the re-cpture dults moved within 25-72 m from the relese points. The movement of ll recovered dult weevils ws within 72 m from the relese point during this relese period (Nigg et l. 23). This movement informtion hs een useful for chrcteriztion of reltionships etween citrus trees, soils nd Diprepes root weevil. If the root weevil dults tend to remin reltively close to where they emerge from the soil, then the root weevil popultion might e relted to soil nd wter vriles tht my influence the performnce of trees on which the weevils feed (Li et l. 23, 25). Synthesis of citrus tree iotic nd iotic stress Plnt iotic stress is signled y low lef wter potentil nd stomtl conductnce (Jones et l. 23; Li et l. 24). Aiotic stress of citrus trees ssocited with flooding, wterlogging, high soil cidity nd unlnced nutrient hs received much ttention in Florid (Syvertsen et l. 1983; Orez nd Collin 22; Li et l. 24). Citrus rootstock physiologicl growth process nd stomtl regultion re sustntilly influenced y flooding nd high cidity (Li et l. 26). Among the most importnt fctors tht could influence citrus tree helth sttus, ir/soil tempertures, soil wter, ph, nd Fe, Mg nd C concentrtions were ssocited with Diprepes weevil development ptterns (Li et l. 24, 27). Since Diprepes lrve, pupe nd tenerl dults re soil-hiting, soil physicl nd chemicl chrcteristics could influence lrvl development nd dult weevil density. This finding hs een consistent in severl greenhouse simultion studies (Rogers et l. 2; Li et l. 23, 24, 26, 27), nd series of field studies in different citrus orchrds cross centrl nd southern counties in Florid (Nigg et l. 21, 23; McCoy et l. 23; Li et l. 23, 24, 27, 27c, 27d). Citrus trees were vulnerle to ttck y the Phytophthor-Diprepes weevil complex in fine-textured, poorly drined soils (Grhm et l. 23). A vriety of pproches of chemicl nd iologicl controls hve een tested ut s no effective nd sfe control methods hve een found, this species is still spreding. Becuse of the smll size, neonte lrve re virtully impossile to detect in the soil nd the initil injury to roots cn e difficult to quntify (Jones nd Schroeder 1983; Rogers et l. 2). Citrus tree decline symptoms re not pprent until the lrve re well-estlished on the roots nd extensive dmge hs occurred (Grhm et l. 23). Individully, iotic stress of dult weevil lef feeding nd lrvl root feeding pressures of Diprepes root weevil hve een the suject of intensive reserch in Florid (Nigg et l. 21; Grhm et l. 23; Li et l. 23; Nigg et l. 23; Li et l. 26, 27). It is reported tht Diprepes root weevil lrve cn consume 2-8% of the citrus seedling roots within six weeks of infesttion (Rogers et l. 2). Long period feeding of Diprepes lrve cn rek the resistnce of citrus roots to infection y Phytophthor spp., nd oth lrvl feeding nd disese cn led to tree decline to n unproductive stte or deth y extensive lrvl root injury (Grhm et l. 23). Temperture would e likely to hve significnt effect on occurrence, timing, development, dispersl nd movement of insect pests (White 1984; Mttson nd Hck 1987; Viens nd Bosch 2; Li et l. 27c, 28). Wrm temperture cn cuse insect outrek, chnge insect ehvior nd influence efficcy of insecticides on pest control (Vicens nd Bosch 2; Amrsekre nd Edelson 24; Pecock et l. 26). High ir nd soil tempertures cn sustntilly cuse high density of Diprepes root weevil dult popultion in citrus orchrds in Florid (Li et l. 27c). Reducing citrus tree iotic nd iotic stress Mngement of root weevil pest is often otined y repeted folir ppliction of chemicl tretments when pest densities exceed n economicl threshold tht requires tretments (Grhm et l. 23; Byers nd Cstle 25). Typiclly, in the sence of erly detection methods nd effective mngement tools, citrus growers control the Diprepes weevil popultion y four pplictions of insecticides ech yer, nd usully uniform rte is pplied over the orchrd (Li et l. 27d). However, the excess use of costly pesticides cn hrm the environment (Byers nd Cstle 25). Understnding plnt, soil nd insect reltions hs impliction in reducing plnt stress (Li et l. 28). In Florid, simultion studies in the greenhouse hve shown citrus seedling root injury under oth flooding neroic effects nd Diprepes root weevil lrvl feeding pressure (Li et l. 23, 26, 27). Field scle studies Diprepes root weevil life cycle, neonte dropping from tree cnopy to soil, dult weevil emergence from soil, ctive dult weevil popultion nd iologicl control hve een the reserch focus for control of this pest (Lpointe 2; Rogers et l. 2; Nigg et l. 21; Grhm et l. 23; McCoy et l. 23; Nigg et l. 23; Sturt et l. 24). Orchrd scle studies of citrus tree, soil nd Diprepes root weevil were primry 67
Citrus iotic nd iotic stress. Hong Li Fig. 2 Citrus orchrd lyout in Osceol County. The trees were 2-yer old Hmlin ornge trees on Single rootstock. Fig. 1 Citrus orchrds tht reltionships of citrus trees, soils nd Diprepes root weevil were ssessed during 21-24. Diprepes root weevil dult popultion hs een surveyed cross six counties in center nd southern Florid: Lke County, Osceol County, Polk County, Indin River County, DeSoto County nd Hendry County. Some of the dt were reported in Futch (23) nd Li et l. (23, 24, 25, 27, 27c, 27d). done in the six counties cross center nd southern Florid: Lke County, Osceol County, Polk County, Indin River County, DeSoto County nd Hendry County (Fig. 1). Citrus tree iotic nd iotic stress prolems hve een ssessed in different orchrds cross center, southern nd south-western counties of Florid (Nigg et l. 21, 23; Grhm et l. 23; Li et l. 23, 24, 26, 27). The mesurements include the susceptiility of citrus rootstocks to Phytophthor disese ssocited with Diprepes lrvl root feeding injury (Grhm et l. 23), tree helth rting, tree cnopy volume nd ornge fruit yield relted to soil physicl nd chemicl conditions nd Diprepes dult popultion development (Li et l. 24, 25). The effects of flooding nd lrvl feeding on citrus rootstock shoot growth nd root injury, multi-yer sptil nd temporl overly ptterns of citrus tree decline, Diprepes dult weevil emergence from soils, ctive dult popultion, soil flooding pttern, wter tle, soil wter content, ph, nd soil Fe, C, Mg, K, P, Cu nd Zn concentrtions re nlyzed, quntified nd mpped (Li et l. 23, 24, 27, 27, 27c, 27d). This pper ttempts to summrize the susceptiility of citrus trees to iotic nd iotic fctors (flooding, wterlogging, soil cidity, unlnced nutrient in soil) nd citrus tree mngement informtion from county-scle field studies nd greenhouse simultion studies conducted in Florid. This pper lso ttempts to discuss out using lef stomtl conductnce, soil redox potentil, soil chemicl nd physicl chrcteristics nd root weevil survivl dt in development of mngement tools for reducing citrus tree decline from iotic nd iotic stress. Time series models nd exponentil growth models would e useful for reducing the cost of field monitoring nd for less frequent spry for integrted citrus tree mngement. CITRUS TREE DECLINE UNDER ANAEROBE, HIGH SOIL IRON AND ROOT WEEVIL FEEDING The simultneous occurrence of soil hiting root weevil, soil cidity, wterlogging nd wter-relted soil chemicl components hs een chllenge for sustinility mngement of citrus orchrds. Citrus tree decline in reltion to soil conditions nd Diprepes root weevil infesttion ws ssessed in 9.5-h citrus orchrd in Osceol County, Centrl Florid (28 22 N, 81 58 W) in 22 (Fig. 2). The site ws locted out 5 m in the south of Lke Tohopeklig, the lrgest lke (76 km²) in Osceol County. The citrus trees were Hmlin ornge trees on Swingle citrumelo rootstock (Citrus prdisi Mcfd. x Poncirus trifolit (L.) Rf.), 2-yr old, plnted on rised 2-row eds with dringe furrows etween the eds, 17 m prt (Fig. 3). In the study re, there were totl of 149 mture trees nd 758 young trees replnted in 2 for reserch purposes (Fig. 3). All trees received regulr liming, irrigtion nd fertiliztion sed on regionl recommendtion ut no chemicl tretments for pest control (Li et l. 24). The mture trees hd een infested y Diprepes root weevil during the lst 1 yers in the orchrd. Two yers (2 nd 21) of dt showed tht dropping numers of Diprepes root weevil lrve from the tree cnopy verged 37 nd 94 neontes per m 2 of soil surfce under tree cnopy (McCoy et l. 23; Nigg et l. 23). Lrvl numers in the soil under tree cnopy were on verge of 5 lrve per m 3 of fresh soil, mesured y tree removl (n = 6 trees) nd sieve smpling round the centrl root re (McCoy et l. 23). The soils, formed in the fltwoods sediments, were clssified s lomy Mollisol (USDA-NRSC 23). Flooding occurred, depending on rin pttern, ecuse of high rinfll (138 mm per yer) nd low elevtion (depression t the lke), cusing soil redox potentil (E h ) fr elow zero (- 26 mv) in flooded res (Fig. 4). Wter tle depth, component for distinguishing the soil unsturted nd sturted zones, vried etween.6-1.4 m cross the orchrd during dry period (Fig. 5A). Soil electricl conductivity (SEC) showed negtive correltion with wter tle depth s the SEC ws high in the deep wter tle res (Fig. 5B). The soils (-.3 m in the depth) were smpled ner (.3 m) tree trunk to evlute the reltionship etween tree decline nd soil wter nd nutrient conditions (Li et l. 24). A totl of 5 soil smples were tken in 34 x 25 m grid cross the orchrd. The soils were ir-dried nd Mehlich I extrcted ctions nd nions (P, K, Mg, C, B, Zn, Mn, Fe nd Cu) were nlyzed using n inductively coupled rgon plsm emission spectrophotometer (Horwitz 2). As the result of wterlogging, the soil in the orchrd ws highly cidic (ph 4.9 ±.4) nd high in Fe concentrtions (36 ± 14 mg kg -1 ). Acid soils contin high levels of ctive hydrogen nd/or luminum in reltion to C nd Mg, nd plnts hve limited tolernce to low ph (Kidd nd Proctor 21). Soil liming dds considerle mount of C nd Mg to the soil ut too much C nd Mg in the soil cn interfere with the vilility of other nutrients (Sopher nd Bird 1982; Bohn et l. 21). Iron (Fe), micronutrient for plnt growth, de- 68
Tree nd Forestry Science nd Biotechnology 3 (Specil Issue 1), 66-78 29 Glol Science Books Klig muck Flooding res 14 Jn. 23 Flooding res 1 Jn. 23 Flooding res 3 Dec. 22 Floridn sndy snd Pined sndy lom Sturtion or wet res during the flooding period Flooding re Sturtion or wet res Fig. 3 Osceol citrus orchrd study. Mp of the citrus tree ( Hmlin ornge trees on Swingle rootstock) rting t the Osceol study site in 9.5-h citrus orchrd with soil type oundry, tree, tree ed nd Tedders trp loctions, tree rting, nd flooding res. T, trnsect (tree ed); T-W, west trnsect; T-WC, west-center trnsect; T-C, center trnsect; T-EC, est-center trnsect; T-E, est trnsect. Re-printed from Li H, Futch SH, Sturt RJ, Syvertsen JP, McCoy CW (27) Assocition of soil iron with citrus tree decline nd vriility of soil ph, wter, mgnesium nd Diprepes Root weevil: two-site study. Environmentl nd Experimentl Botny 59, 321-333, 27, with kind permission from Elsevier Pulisher. Flooded E h = - 26 mv (n = 3) Non-flooded E h = + 24 mv (n = 3) Fig. 4 Osceol citrus orchrd study. Flooding occurred fter period of rin. Flooded noxic soil hd negtive soil redox potentil E h tht cused tree decline. creses significntly when soil ph increses from 5 to 6 (Sopher nd Bird 1982; Bohn et l. 21). High concentrtions of Fe 2+ in the soil solution could form plque to ffect sorption of nutrients y roots (Liu et l. 27). Citrus tree decline ws ssessed y visul quntifiction of tree decline symptoms using the chrcteristics defined y Blzquez (1991). The tree rnking ws ssessed using numericl 1-4 rnking system s follows: 1 = severe decline, 2 = moderte decline, 3 = decline, nd 4 = slight decline. The tree chrcteristics in rting ws: 1 = cnopy esily seen through, flush on mjor lims only or on less thn hlf of the tree, leves smll); 2 = moderte decline (cnopy esily seen through, flush on secondry nd higher lims scttered round the entire cnopy, leves smll); 3 = decline (well-defined cnopy, more thn hlf of which cnnot e seen through, flush on secondry nd higher lims, leves lrge); nd 4 = slight decline (well-shped nd welldefined cnopy tht cnnot e seen through, flush on secondry nd higher lims, leves lrge nd green) (Li et l. 24). More severe decline nd decline trees were situted in the flooded re thn non-flooded res (Fig. 3). The regression plot of tree helth rting (THR) ginst soil Fe concentrtion showed tht tree decline ws linerly correlted to soil Fe t the Osceol site (Fig. 6). More thn 5% of the severely decline (rting 1) nd modertely decline (rting 2) trees were situted with high soil Fe concentrtion of 4-8 mg kg -1. Severely decline nd modertely decline trees were 6.2% of the totl infested trees. Only two trees of rting 3 (decline trees, or 3.9% of totl infested trees) were with soil Fe concentrtion > 4 mg kg -1. All the helthier trees (rting 4, slight decline) were in res low in Fe concentrtions etween 13 nd 39 mg kg -1 (Li et l. 27). Severe citrus tree decline ws found in shllow wter tle res nd flooded res, where the stomtl conductnce (g s ) of mture, top young leves of the citrus rootstock seedlings decresed from 152 mmol m -2 s -1 to 94 mmol m -2 s -1 under the flooded conditions (Fig. 7). However, lef wter potentil P did not differ mong trees in the flooded res (.66 ±.18 MP) vs. the non-flooded res (.66 ±.1 MP) (Li et l. 24). Stepwise multiple liner models for tree helth rting (THR) relted to SWC (g kg -1 ), soil ph, nd soil Fe (mg kg -1 ) showed the trends s follows: THR = 4.6598.34SWC.353pH.326Fe R 2 =.26, P <.87 [1] The model Eq. [1] ws lso significnt (F = 4.37, df = 3, 46), nd the estimte prmeters were significnt for the intercept (P <.343), nd Fe (P <.17) (Li et l. 27). Too much Fe in soil could ffect plnt growth s shown 69
Citrus iotic nd iotic stress. Hong Li Shllow A B Soil EC (ms/m) Fig. 5 Osceol citrus orchrd study. Sptil ptterns of wter tle (A) nd soil electricl conductivity (B) cross the Oseceol citrus orchrd. Deep Wter tle depth (m) Medium Tree helth rting (THR) Slight decline Decline Moderte decline Severe decline THR = -.271Fe + 3.4533 r = -.42, P <.1, n = 5 2 4 6 8 1 Soil Fe concentrtion (mg kg -1 ) Fig. 6 Osceol citrus orchrd study. Regression reltionship of soil Fe concentrtion vs. tree decline rting (1 = severe decline, 2 = moderte decline, 3 = decline, nd 4 = slight decline) on the Mollisol t the Osceol site. Re-printed from Li H, Futch SH, Sturt RJ, Syvertsen JP, McCoy CW (27) Assocition of soil iron with citrus tree decline nd vriility of soil ph, wter, mgnesium nd Diprepes Root weevil: two-site study. Environmentl nd Experimentl Botny 59, 321-333, 27, with kind permission from Elsevier Ltd. Shllow Shllow 94 mmol m -2 s -1 g s dringe could lso result in decresing soil Fe level to reduce tree decline (Li et l. 27). CITRUS TREE ABIOTIC STRESS FROM POOR SOIL REDOX POTENTIAL AND LEAF STOMATAL CONDUCTANCE Plnts demnd oxygen, wter nd nutrients for growth. It is estlished tht flooding cn result in oxygen deprivtion in the root system, nd led to distur plnt-soil system equilirium, dmge in roots nd rrest plnt growth (Pezeshki nd Delune 1998; Oren et l. 21; Li et l. 23, 24, 26). Soil oxidtion-reduction (redox) potentil (E h ), cn e reduced y soil wterlogging, which trnslted into greter demnd for oxygen within the soil nd incresed plnt wter stress (Pezeshki nd Delune 1998; Li et l. 23, 26). Plnt physiologicl responses to flooding stress re reflected y to reduced lef stomtl conductnce (g s ), lef gs exchnge, lef wter potentil (Oren et l. 21; Li et l. 23; Mielke et l. 23; Blnke nd 152 mmol m -2 s -1 g s Fig. 7 Osceol citrus orchrd study. Comprison of plnt lef stomtl conductnce (g s) in flooding nd nonflooding res. Re-printed from Li H, Syvertsen JP, Sturt RJ, McCoy CW, Schumnn A, Cstle WS (24) Soil nd Diprepes root weevil sptil vriility in poorly drined citrus grove. Soil Science 169, 65-662 27, with kind permission from Lippincott, Willims & Wilkins, Wolters Kluwer Pulisher. Deep Deep Flooded plnts Non-flooded plnts Lef stomtl conductnce ( g s ) Medium Medium Shllow Deep y the severely declined trees in res high in Fe concentrtion. The high level of extrctle soil Fe could e due to the low soil ph (4.9), high SWC (26 g kg -1 ) nd flooding (Li et l. 27). Soil Fe concentrtion ws negtively correlted with wter tle depth (r = -.38, P <.1), showing tht high soil Fe concentrtion ws ssocited with high soil wter content. Soil Fe is more solule t low ph level, nd lrge mount of Fe cn ecome ville under neroic conditions (Bohn et l. 21). The increse of extrctle soil Fe concentrtions with incresing SWC nd decresing soil ph re consistent with the Fe chemistry mechnism descried in Sopher nd Bird (1982) nd Bohn et l. (21). These might explin why severely declined trees were ssocited with high soil Fe concentrtions > 4 mg kg -1 (Fig. 6). Thus, incresing soil ph nd improving soil Cooke 24: Li et l. 24). Flooding induced stomtl closure nd lef conductnce nd lef turgor potentil were signi-ficntly reduced in flooded 2-yr old sour ornge plnts (Ruiz-Snchez et l. 1996). In poorly drined citrus grove, flooded trees were more wter stressed thn non-flooded trees, s indicted y lef g s, which ws significntly lower in n re flooded for three weeks thn in non-flooded re (Li et l. 23). In citrus, plnt environmentl stress from flooding cn occur simultneously with root weevil infesttions (Li et l. 23, 24, 24, 26). It is reported tht the Diprepes revitus (L.) root weevil cn e dispersed nursery rootstock into citrus groves nd injury inflicted y Diprepes lrve on roots hs resulted in plnt decline nd deth (Jones nd Schroeder 1983; Quintel nd McCoy 1997; 7
Tree nd Forestry Science nd Biotechnology 3 (Specil Issue 1), 66-78 29 Glol Science Books Tle 1 Greenhouse study. Experimentl tretments nd procedures with two citrus rootstocks Swingle (SWI) nd Smooth Flt Seville (SFS). 1. Flooding procedures (one seedling in ech 13 cm 3 pot) Tretments Rootstock vriety SWI, SFS Flooding (dys) non-lrve (non-flooding & non-lrvl feeding), 8 reps per vriety + 5 lrve fter flooding, 1, 2 nd 3-dy flooding nd 4-dy lrvl feeding, 8 reps per vriety 2. Drining for one week for flooded seedlings fter flooding termintion. 3. Lrvl feeding for 4 dys using flooded nd non-flooded seedlings fter drining procedures. Soil redox potentil (mv) 3 2 1-1 F3 F2 NF F1 NF-ND All tretments Swingle -2 Flooding period Drining Lrvl feeding period period -3 1 5 1 15 2 25 3 35 4 45 5 Fig. 8 Greenhouse study. Temporl ptterns of soil redox potentil for Swingle throughout Experiment I. NF, non-flooded; F3, 3-dy flooded; F2, 2-dy flooded; F1, 1-dy flooded tretments. Ech point represents the men nd stndrd error of 8 mesurements. Re-printed from Li H, Syvertsen JP, Sturt RJ, McCoy CW, Schumnn A (26) Wter stress nd root injury from simulted flooding nd Diprepes root weevil feeding in citrus. Soil Science 171, 138-151 26, with kind permission from Lippincott, Willims & Wilkins, Wolters Kluwer Pulisher. Stomtl conductnce (mmol m -2 s -1 ) 4 35 3 25 2 15 1 5 Flooding dy Flooded seedlings Non-flooded seedlings 1 1 2 3 4 5 6 Experimentl dys Fig. 9 Greenhouse study. Men nd stndrd error of lef stomtl conductnce (g s) two citrus rootstock vrieties (Swingle nd Smooth Flt Seville) y flooded nd non-flooded seedlings cross the period of 6 dys. Ech point represents the men of n = 48 for flooded seedlings nd n = 16 for non-flooded seedlings. Rogers et l. 2). The soil environment influenced plnt growth nd the undnce of most herivorous insects (Orins nd Fritz 1996). Flooding incresed soil ph, decresed nutrient vilility nd lef dry mtter yield (Li et l. 23; Yoo nd Jmes 23) ut lef eetle lrvl pupl weight ws not influenced y nutrient or flooding conditions to the plnt (Lower et l. 23). Flooding events nd soil wterlogging cn e criticl stress fctors for citrus trees. In Florid, citrus is often cultivted on low-lying fltwoods soils with poor dringe (Orez nd Collins 22). Citrus root injuries from lrvl feeding were ssocited with lrvl density, rootstock vriety, soil type nd moisture nd root injury to different rootstocks growing in well-drined soil rnged from 5 to 8% y 4 dys fter infesttion y 2-5 Diprepes neonte lrve, nd mny root tissues were completely consumed fter 79 dys (Rogers et l. 2). However, does plnt growth or root injury e relted to lrvl survivl? Are the responses of flooded trees to lrvl feeding different thn non-flooded trees? Are flood-dmged seedlings more vulnerle or susceptile to lrvl feeding injury thn non-flooded seedlings? Does the comintion of flooding nd lrvl feeding complicte tretments for weevil control? A greenhouse simultion study ws conducted in the greenhouse house to investigte chnges of citrus soil redox potentil, lef stomtl conductnce, plnt growth nd lrvl survivl under flooding nd Diprepes lrvl feeding tretments, how the comined effects of soil flooding nd Diprepes lrvl feeding on citrus tree root dmge. It is expected tht plnts nd lrve to grow etter in non-flooded conditions thn in flooded conditions, ecuse flooding prohiits gs exchnge in the plnt-soil system nd flooded soil is compcted. The studies ttempted to quntify how long seedling plnts cn tolerte flooding stress. The greenhouse study ws conducted t the Citrus Reserch nd Eduction Center, University of Florid. Threemonth old seedlings of two commercil citrus rootstock vrieties, Swingle citrumelo (Citrus prdisi Mcfd x Poncirus trifolit (L.) Rf.) nd Smooth Flt Seville (Citrus urntium L.) were used in the study (Tle 1). The tretment consisted of four levels of flooding durtion (, 1, 2 or 3 dys), nd two levels of Diprepes lrve ( or 5 lrve per seedling), feeding for 4 dys (Tle 1). The design ws 2 vrieties 4 flooding durtions 8 replictes, rrnged in completely rndomized design. There were totl of 8 seedlings. Seedlings were selected for uniformity of root density nd cnopy size for ech vriety efore trnsplnting into 13-cm 3 plstic pot for sumergence. Soil ws Cndler fine snd, ph 6, contining 965 g kg -1 (or 97%) of snd, similr to the verge snd content of citrus soils in Florid (Li et l. 23, 26). The flooding tretments were pplied y sumerging seedlings to 2 cm ove the tops of seedling pots nd the shoots remined in the tmosphere. The 3-dy tretments were sumerged for 1 dys then the 2-dy tretments were flooded. After flooding for 1 more dys, the 1-dy tretments were sumerged (Li et l. 26). As result, the flooding tretments were completed t the sme time. All flooded seedlings were removed from the wter then put for dringe (Tle 1). All flooding tretments (, 1, 2 or 3 dys) were infested y 5 Diprepes neonte lrve per seedling week of dringe. There ws control for non-flooding nd nonlrvl feeding (NF-ND), which consisted of 2 vrieties 8 replictes. One-dy old Diprepes lrve were inoculted to the soil for ll feeding tretments week fter completing the flooding procedure (Tle 1). The seedlings were not flooded during the lrvl feeding period. Except the flooding period, ll tretments received the sme rtes of fertilizers nd wters. Tempertures in the greenhouse vried etween 28 ± 4 C throughout the experiment (Li et l. 26). The results of the study showed tht the soil redox potentil (E h ), mesured using the Orion oxidtion-reduction proe, decresed ruptly following sumergence of ech tretment nd the E h ecme negtive within 1-3 dys of flooding (Fig. 8). The soil E h vried within -1 nd -18 mv nd it showed complete lck of oxygen tht ws ttined s quickly s 1 dy fter sumergence (Li et l. 26). Lef stomtl conductnce (g s ), mesured using the Delt-T A4 porometer, decresed significntly within in- 71
Citrus iotic nd iotic stress. Hong Li Tle 2 Greenhouse study. Anlysis of vrince for citrus seedling lef stomtl conductnce (g s) nd soil redox potentil (E h) during flooding period of two rootstocks Swingle nd Smooth Flt Seville. Sources df Soil E h Lef g s Model 42 236** 7.25** Rep 7.55 ns 2.69* Vriety (V) 1.47 ns 89.5** Flood (F) 3 3286** 7.3** Rep x V 7.44 ns 1.9 ns V x F 3 8.** 43.1** Rep x F 21.56 ns 1.5 ns R 2.99.94 : ns, not significnt; *, P <.5; **, P <.1. Re-printed from Li H, Syvertsen JP, McCoy CW, Schumnn A (23) Soil redox potentil nd lef stomtol conductnce of two citrus rootstocks sujected to flooding nd Diprepes root weevil feeding. Proceedings of the Florid Stte Horticulturl Society 116, 252-256, 23, with kind permissions from Florid Stte Horticulturl Society. cresing flooding durtion (Fig. 9). The g s vlues strted to decrese fter 2 dys of flooding nd then decresed consistently with durtion of flooding (Li et l. 26). The g s vlue ws high (35 mmol m -2 s -1 ) efore flooding ut it ws s low s 4 mmol m -2 s -1 y the end of 3 dys of flooding (Fig. 9). The nlysis of vrince, determined using PROC GLM procedure (SAS, 199), showed tht flooding tretment hd the significnt effects on soil E h (F = 3286, df = 3, P <.1) nd citrus lef g s (F = 7.3, df = 3, P <.1). The interction etween vriety nd flooding ws lso significnt on soil E h (F = 8., df = 3, P <.1) nd citrus lef g s (F = 43, df = 3, P <.1).The ontrst showed lso tht soil E h nd citrus lef g s were significntly different etween Flooding tretments (Tle 2). Shoot growth ws significntly higher in the control (non-flooded) thn in flooded tretments for oth rootstocks (Fig. 1A, 1B), which ws result of stronger root development in the non-flooded seedlings (Fig. 1C, 1D). Shoot growth of citrus tree seedlings rrested during the flooding period. Root injury, estimted y clssifying the whole seedling root system y percentge dmge s % (control), -25%, 25-5%, 5-75%, nd >75% dmge, ws minly ttriuted to flooding neroic (Li et l. 26). Flooded soil ph ws found to increse with flooding durtion. The ph vlue of 4-dy floodwter incresed y.7 units y the end of 4-dy flooding period compred to.3 units for the 2-dy flooding tretments. However, chnges in flooding wter hd no significnt effects on seedling shoot growth (Li et l. 26). The effect of flooding ws significnt on shoot growth nd root rting for the two rootstock vrieties (Li et l. 26). With initil shoot lengths of 39.4 ± 3.9 cm in SWI nd 27.6 ± 6.4 cm in SFS, shoot lengths grew fster in SWI (2.7 ± 1.5, 1.5 ± 1.2, nd.3 ±.6 cm) thn in SFS (.3 ±.5,.4 ±.7, nd.3 ±.4 cm) for the F1, F2 nd F3 tretments, respectively, during the flooding period. However, during the lrvl infesttion period, shoot growth ws greter in SFS (3.1 ± 5.1, 1.4 ± 1.8, nd.1 ±.1 cm) thn in SWI (.2 ±.1,.1 ±.1, nd.3 ±.3 cm) for the previously flooded F1, F2 nd F3 tretments, respectively. There were significnt differences in shoot growth for lrvl feeding tretments compred to non-lrvl feeding tretments (Tle 3). Citrus rootstocks could vry in their responses to flooded soil conditions nd citrus lef hydrulic conductivity nd stomtl conductnce were reduced significntly under flooded neroic conditions (Syvertsen et l. 1983; Li et l. 23). It ws reported tht the ility of citrus seedlings to tolerte lrvl feeding differs mong rootstocks, nd the correltion etween root loss nd lrvl weight gin ws significntly positive (Li et l. 24). The ssessment of the degree of plnt physicl stress from soil flooding events y mesuring plnt lef stomtl conductnce (g s ) hs yielded the insights of reltionship of soil wterlogging nd citrus tree decline in the humid environment. Citrus rootstocks showed mximum cpcity of three weeks to resist to flooding dmge ut ten dys of flooding showed the significnt effect on lowing lef stomtl conductnce nd slowing shoot growth of citrus rootstocks (Li et l. 26). Shoot growth (cm) No lrve With lrve 1 1 A B SWI SFS SWI SFS 8 8 c 6 6 c 4 2 d c 4 2 Shoot growth (cm) Root dry weight (g) 24 2 16 12 8 4 SWI c C SFS c SWI c D SFS c 24 2 16 12 8 4 Root dry weight (g) NF F2 F3 NF F2 F3 Flood tretments NF F2 F3 NF F2 F3 Flood tretments Fig. 1 Greenhouse study. Comprison of shoot growth (A-B) nd root dry weight (C-D) with nd without Diprepes lrvl feeding. The tretments were SWI, Swingle; SFS, Smooth Flt Seville; NF, non-flooded; F2, 2 dy-flooded; F3, 3 dy-flooded. Ech r represents the men nd stndrd error of 8 seedlings. Re-printed from Li H, Syvertsen JP, Sturt RJ, McCoy CW, Schumnn A (26) Wter stress nd root injury from simulted flooding nd Diprepes root weevil feeding in citrus. Soil Science 171, 138-151 26, with kind permission from Lippincott, Willims & Wilkins, Wolters Kluwer Pulisher. 72
Tree nd Forestry Science nd Biotechnology 3 (Specil Issue 1), 66-78 29 Glol Science Books Tle 3 Greenhouse study. Contrst for soil redox potentil (E h), lef stomtl conductnce (g s), shoot length, lrvl survivl, nd root rting for flooding nd non-flooding tretments of two citrus rootstocks (Swingle nd Smooth Flt Seville). Seedlings n = 8 per flooding nd non-flooding tretment per rootstock. Contrsts df E h g s Shoot length Lrvl survivl Root rting Flooding period NF vs. F 1 118** 8.22** 15.6** F1 vs. F2 1 7.96** 4.6* ns 4.7* F1 vs. F3 1 6395** 17.1** 7.6** Lrvl feeding period ND vs. D 1 45.7** 3.7 ns 8.6** 6.8** NF-ND vs. NF-D 1 2.5 ns.1 ns 3.2 ns 6.* F1-D vs. F2-D 1 1.4 ns 5.7* 1.2 ns 26.4** 27.1** F1-D vs. F3-D 1 3.5 ns 14.** 2.1 ns 461.7** 41.3** F vlues. ns, non significnt, nd * nd **significnt t P <.5 nd P <.1. F1, 1-dy flooded; F2, 2-dy flooded; F3, 3-dy flooded; F4, 4-dy flooded tretments. ND, no-diprepes lrve; NF, non-flooded tretments. Re-printed from Li H, Syvertsen JP, Sturt RJ, McCoy CW, Schumnn A (26) Wter stress nd root injury from simulted flooding nd Diprepes root weevil feeding in citrus. Soil Science 171, 138-151 26, with kind permission from Lippincott, Willims & Wilkins, Wolters Kluwer Pulisher. CITRUS TREE TOLERANCE TO LARVAL FEEDING AND ROOT WEEVIL LARVAL SURVIVAL Becuse root wterlogging nd lrvl feeding occur underground, the identifiction of specific underground infesttion sites for root weevils might reduce the re to tret nd could contriute to reduced tretment costs for chemicl nd iologicl control (Li et l. 24). As Diprepes neonte lrve invde the soil fter htching from eggs lid y dults in the citrus cnopy nd lrve feed on tree roots nd susequently pupte in the soil, injury inflicted y Diprepes lrve cn result in tree decline nd deth (Rogers et l. 2). However, the initil injury to roots cn e difficult to quntify. It is reported tht the ility of citrus seedlings to tolerte lrvl feeding differs mong rootstocks, nd the correltion etween root loss nd lrvl weight gin ws significntly positive (Rogers et l. 2; Li et l. 24). Root injury of different rootstock seedlings growing in well-drined sndy soil vried etween 5 to 8% within 4 dys of inocultion of 2-5 Diprepes neonte lrve, nd mny root tissues were completely consumed fter 79 dys (Rogers et l. 2). The reltive vulnerility of citrus rootstock seedlings to Diprepes root weevil lrvl feeding injury, determined in the ove greenhouse simultion study (methods detiled in previous section), showed tht root injury y lrvl feeding incresed with the durtion of previous flooding. The injury rnged etween -3% of roots for the non-flooded rootstock seedlings, -6% of roots for the 1-dy flooded nd 2-dy flooded seedlings, nd 3-12% of roots for the 3-dy flooded seedlings in oth Swingle nd Smooth Flt Seville vrieties (Li et l. 26). These mesurements showed tht citrus seedling root injury ws ttriuted to oth flooding nd lrvl infesttion. As compred to the control (non-flooded) seedling roots, whole seedling root dmge y flooding nd lrvl feeding incresed with flooding durtion. Aout 25-5% of root dmge ws found in rootstock seedlings previously flooded for 2 dys, nd root dmge incresed significntly to 5-75% for rootstock seedlings tht were previously flooded for 3 dys (Li et l. 26). Lrvl survivl ws significntly different etween the previously flooded tretments (P <.5, Li et l. 26). With n initil infesttion of 5 neonte lrve per seedling, the lowest lrvl survivl ws found in the non-flooded tretment (6 ± 22%), nd the survivl rte ws significntly greter in the longest flooded tretments, 3-dy flooded (88 ± 1%) for oth vrieties (Li et l. 26). In ddition, difference in lrvl survivl ws found etween the two citrus rootstock vrieties (Swingle, 78 ± 22%; nd Smooth Flt Seville, 82 ± 14%). Totl weight of survivl lrve vried etween 25 nd 182 mg per seedling. The initil lrvl weight ws on verge.5 mg (5 1-dy old neontes). Lrvl weight incresed y 5-364 times fter 4 dys of feeding on seedling roots, indicting strong growth (or feeding) potentil of neonte lrve. Lrvl growth ws the highest in the non-flooded tretments. It might e ecuse less flooding compction would men etter ertion in the sndy soil tht could e more fvorle to lrvl survivl (Li et l. 26). Flooded nd wterlogged soils were typiclly more compcted with higher ulk density thn non-flooded soil (Sqi et l. 24). In other seprte greenhouse study with lomy soil, lrvl survivl ws significntly lower, 66 ± 19% for Swingle nd 5 ± 22% for Smooth Flt Seville seedlings flooded 2-4 dys (Li et l. 27). It ws reported tht n increse of.5 unit ph in the flooded soil could reduce significntly lrvl survivl (Li et l. 27c). In other studies, surviving numers nd ctivity levels of lrve were significntly reduced in the tretment with low ph of 5, high nitrte exposure levels of 2 mg L -1 (Htch nd Blustein 2). A significnt increse in soil ph ws found in flooded soil (Yoo nd Jmes 23). It is suggested tht 2-dy flooding durtion is the threshold for citrus rootstock seedling plnt wter stress nd root injury from flooding dmge (Li et l. 24). Citrus rootstock seedling roots could e injured y wterlogging nd lrvl feeding. A negtive soil redox potentil nd decrese in lef stomtl conductnce could e n erly indictor of plnt wter stress nd root dmge from flooding, nd soil type nd soil texture could lso e fctors ffecting lrvl survivl in the field. There is need for more informtion out the ssocitions of wterlogging, redox potentil, soil ph, soil texture, nd lrvl survivl for citrus rootstock protection. Soil-inhiting Diprepes lrvl survivl nd growth were relted to citrus rootstock, soil type nd soil moisture in the greenhouse studies (Rogers et l. 2; Li et l. 24, 26). The cuses relted to lrvl survivl were complex. Some experimentl dt showed tht erly lrvl survivl ws more sensitive to cid stress (low ph) nd high Al nd NO 3 nd Cl slt solutions hd the toxicologicl effects on the numer of surviving lrve (Schrder et l. 1998; Htch nd Blustin 2). Diprepes root weevil lrvl survivl nd growth could reduce from 8% to 6% when soil ph incresed from 4.8 to 5.6 in cidic soil (Li et l. 27c). IMPLICATION OF TIME SERIES MODEL IN ROOT WEEVIL CONTROL FOR REDUCING CITRUS BIOTIC STRESS Economic costs from citrus tree infesttion of Diprepes root weevil nd the ssocited root disese in citrus could e s much s $6 per hectre (Grhm et l. 23). The relted mngement for tree protection hs een spryed with four pplictions of insecticides ech yer with one ppliction in ech seson. However, field monitoring of insect popultions for tretment determintion could e criticl ecuse of the time nd lor cost. Mthemtic models were useful to define prolems, understnd the systems, nd 73
Citrus iotic nd iotic stress. Hong Li Fig. 11 Hendry citrus orchrd study. Soil units (Boc snd, Alfisol; Choee fine sndy lom, Mollisol), soil type oundries nd trp loctions for monitoring Diprepes root weevil dults fter emerging from the soil (n = 1) under Swingle rootstock tree cnopy. Re-printed from Li H, Futch SH, Syvertsen JP, McCoy CW (27d) Time series forecst nd soil chrcteristicssed simple nd multivrite liner models for mngement of Diprepes revitus (L.) root weevil in citrus. Soil Biology nd Biochemistry 39, 2436-2447 27, with kind permission from Elsevier Ltd. mke predictions for purposes of insect nd soil mngement, which hve shown n ility to predict insect development ptterns to reduce costs from monitoring field dt (Worner 1991; Toin et l. 21; Byers nd Cstle 25; Crowder nd Onstd 25; Li et l. 27, 27d). These models included time-step simultion models, non-liner degree-dy models, nd est-fit polynomil nd exponentil regression models. If Diprepes root weevil development ptterns were ssocited with time nd ir/soil tempertures (Li et l. 27c), mthemticl equtions derived from their correltions in susequent yers would e useful for the weevil control through predicting its development pttern with time (Li et l. 27d). The development of Diprepes root weevil popultion ws monitored in fltwoods citrus orchrd in Hendry County, south Florid (26 44 37 N, 81 31 33 W). The citrus trees were 1-yer old Hmlin ornge trees on Swingle citrumelo rootstocks, plnted in high density (3 8 m), 2-ed rows. The trees hd een infested y Diprepes root weevils during the 6 yers prior to the eginning of the study, nd the ornge fruit yield in the orchrd vried etween 36-5 Mg h -1 (Li et l. 27d). The Diprepes root weevil popultion ws monitored in 3 12 m grid using 1 pyrmidl Tedders trps cross period of three yers (21-23). During the study period, the citrus trees received regulr grove cre including irrigtion, fertiliztion, nd pest control using the regionl recommendtion (Li et l. 27d). In the Diprepes root weevil monitoring res, there were two soil types, Boc snd (Alfisols) nd Choee fine sndy lom (Mollisols), formed in thick eds of sndy nd lomy mrine sediments (USDA- NRCS 23). Boc snd zoned etween Choee fine sndy lom (Fig. 11). The Boc soil is modertely permele soil nd the Choee soil is slowly permele soil. Due to low elevtion in the depression, the Boc snd nd Choee lom were poorly drined. The dringe system in the orchrd consists of dringe furrows in every 4 rows of trees for evcuting surfce wter (Li et l. 27d). The dt showed tht totl of 962, 945 nd 549 dult weevils were trpped in 21, 22 nd 23, respectively (Li et l. 27d). The weekly dult density vried etween 5.5-9.6 weevils per trp (Tle 4). The weevil popultion ws more undnt in the est nd south thn other res cross the orchrd ech yer (Fig. 12). The higher weevil density ws found in the Mollisol soil, nd the interpolted res of high weevil density were limited to the Mollisol (Choee lom) nd some trnsition res cross the Alfisol (Boc snd) during the three yers (Fig. 12). The weevil popultion peked in the spring when the tempertures were wrm up to 25 C ech yer. For exmple, the dult popultion peked in lst week of April (112 weevils) nd the second week of My in 21 (13 weevils). The ctive weevil density ws on verge.23 ±.18 weevils m -2 cross the three yers nd the highest density ws.91 weevils m -2, monitored in 21. Difference in weevil density etween the three yers ws significnt (ANOVA, F = 8.9, df = 2, 297, P <.2), nd the contrsts showed significnt difference in weevil density for 21 vs. 23 (F = 13.9, P <.2), nd 22 vs. 23 (F = 12.78, P <.4) (Li et l. 27d). From the strt of the yer to the popultion pek in the spring, the cptured dult Diprepes weevils showed n exponentil pttern ech yer. Up until the popultion pek (within the first 19-21 weeks of the yer), the growth of the weevil popultion (Di) with time (t, week) could e descried y the exponentil equtions s shown in Li et l. (27d) s follows: 21: Di = 7.747e.1333t (R 2 =.72, P <.1) [2] 22: Di = 8.2465e.1461t (R 2 =.7, P <.1) [3] 23: Di = 3.259e.1557t (R 2 =.54, P <.5) [4] The outrek of Diprepes dult weevils from the strt of the yer (mid Ferury) to the pek in the spring (April- My) exhiited n exponentil trend of insect growth (Fig. 6). The threshold weekly tempertures for the root weevil outrek were 2-27 C s men ir temperture nd 22-29 C s men soil temperture (Li et l. 27d). The exponentil growth of the Diprepes weevil popultion showed the est fit y the 3-yr men popultion (R 2 =.81, P <.1, Li et l. 27c). The growth of popultion ws exponentil in theory when popultions were in the initil growth 21 A 22 B 23 C Fig. 12 Hendry citrus orchrd study. Interpolted sptil ptterns of Diprepes dult root weevil density (dults per 3 12 m 2 ) in 21 (A), in 22 (B) nd in 23 (C). Re-printed from Li H, Futch SH, Syvertsen JP, McCoy CW (27d) Time series forecst nd soil chrcteristics-sed simple nd multivrite liner models for mngement of Diprepes revitus (L.) root weevil in citrus. Soil Biology nd Biochemistry 39, 2436-2447 27, with kind permission from Elsevier Ltd. 74
Tree nd Forestry Science nd Biotechnology 3 (Specil Issue 1), 66-78 29 Glol Science Books Tle 4 Hendry citrus orchrd study. Descriptive sttistics of weekly Diprepes root weevil popultion monitored in 21, 22 nd 23, grvimetricl soil wter content (SWC), time domin reflectory volumetric wter content (TDR), cly, snd, silt, soil orgnic mtter content (SOM), nd Mehlich-I extrctle nutrient vriles determined in 23 (n = 1). Vrile Men SD Min. Mx. Kurtosis Skewness CV (%) Di1 9.6 9. 38..7 1.2 93.2 Di2 9.5 8.5 35..2 1. 9.3 Di3 5.5 5.6 22. 1. 1.3 11.3 SWC.52.38.3.167.294 1.39 73.5 TDR.71.65.2.27 2.252 1.735 91.4 Snd 96 44 754 986.5 -.7 4.9 Cly 34 28 1. 12 -.2.5 83.4 Silt 6 39 8. 246 5.3 2. 65.3 SOM 1.1 5.7 2. 24.7 -.8.4 56.4 CEC 7.8 6.1 1.8 26.5 2.5 1.7 78.2 ph 6.3.7 4.8 7.5 -.9 -.3 11.8 P 27 16 5.5 7 -.3.6 57.9 K 38 3 5. 179.5 3.4 1.3 79. Mg 78 54 1 237 -.3.8 69.7 C 156 116 174 4799 4.5 2.3 14.7 Mn 4.2 1.3 1.7 8. -.3.2 31.5 Fe 31 6.8 14.1 45.8 -.2.2 22.1 Weekly Diprepes dult popultions in 21, in 22, nd in 23, respectively. SWC, grvimetric soil wter content (kg kg -1 ), TDR, volumetric soil wter content (m 3 m -3 ), snd, cly, silt in g kg -1, orgnic mtter content (g kg -1 ), CEC in (Cmol kg -1 ), nd P, K, Mg, C, Mn nd Fe in mg kg -1. Re-printed from Li H, Futch SH, Syvertsen JP, McCoy CW (27d) Time series forecst nd soil chrcteristics-sed simple nd multivrite liner models for mngement of Diprepes revitus (L.) root weevil in citrus. Soil Biology nd Biochemistry 39, 2436-2447 27, with kind permission from Elsevier Ltd. Tle 5 Hendry citrus orchrd study. Correltion etween weekly men Diprepes root weevil density in 21, 22, 23, nd 3-yr weekly men Diprepes root weevil density relted to grvimetricl soil wter content (SWC), time-domin-reflectory volumetric soil wter content (TDR), soil texture (snd, cly, nd silt), orgnic mtter content (SOM), ph, ction exchnge cpcity (CEC), nd mcro nd minor soil nutrients (P, K, Mg, C, Mn nd Fe). Vriles Di1 Di2 Di3 3-yr Di Person correltion coefficient (r) Di2.63** 1 Di3.47**.56** 1 3-yr Di.88**.86**.77** 1 SWC.37**.52**.42**.51** TDR.36**.47**.39**.48** Snd -.34** -.34** -.33** -.4** Cly.38**.52**.55**.56** Silt.11 ns.1 ns -.3 ns.5 ns SOM.44**.55**.55**.6** ph -.23* -.4 ns -.11 ns -.17 ns CEC.38**.57**.54**.57** P.23*.35**.29**.34** K.42**.53**.55**.58** Mg.49**.65**.53**.65** C.32**.52**.48**.5** Mn.28**.26**.14 ns.28** Fe.14 ns.32**.19 ns.24* Diprepes root weevil popultion in 21, 22, 23, nd 3-yr totl popultion (3-yr Di). n = 1. : ns, * nd **, non significnt, significnt t proility P <.5 nd P <.1. Re-printed from Li H, Futch SH, Syvertsen JP, McCoy CW (27d) Time series forecst nd soil chrcteristics-sed simple nd multivrite liner models for mngement of Diprepes revitus (L.) root weevil in citrus. Soil Biology nd Biochemistry 39, 2436-2447 27, with kind permission from Elsevier Ltd. phses t the strt of the seson when competition nd dmge-induced plnt stress should hve less influence (Byers nd Cstle 25). It is suggested tht increses in temperture hve numer of implictions for meteorology-dependent insect pests in spce nd time (Li et l. 27c). The study found tht the weevil density ws.4,.42 nd.27 weevils per m 2 in the slowly permele Mollisol ginst.17,.14 nd.64 weevils per m 2 in the modertely permele Alfisol in 21, 22 nd 23, respectively. The honestly significnt difference (HSD) ws.67 weevils per m 2 in the slowly permele Mollisols nd.28 weevils per m 2 in the modertely permele Alfisols (Li et l. 27d). The soil nlysis found lso tht soil physicl nd chemicl chrcteristics were vrile (Tle 5) nd soil wter content, orgnic mtter, nd Mg, K nd P concentrtions were high within the Mollisol (Fig. 13). The correltion nlysis found tht Disprepes root weevil dult popultion development ws positively correlted (P <.5) to soil wter content, cly content, orgnic content, nd P, K, Mg, C nd Mn concentrtions (Tle 5). Since most life stges including lrve, pupe nd tenerl dults occur in soil (McCoy et l. 23; Nigg et l. 23), nd chrcteristics of the soil nd the citrus trees on which root weevil feed cn directly or indirectly influence dult weevil development (Li et l. 24, 25, 27, 27d). Soil nutrients influence citrus tree cnopy performnce (Alv et l. 23) nd soil orgnism cycles (Klironomos et l. 1999). The weevils might e more ttrcted to igger, helthier, fuller trees for feeding nd egg lying for more undnt dult occurrence (Li et l. 24, 27, 27d). Using the moving verge forecst model (SAS Institute 1993), the future Diprepes popultion pttern ginst time (t) is estimted s the verge of the lst N monitoring of the underlying time series, which cn e the 3-yr mens of the weekly Diprepes field monitoring dt. The simple un-weighted moving verge model is descried y the eqution s shown in Li et l. (27d) s follows: Dit Dit 1 Dit 2... Dit j Di t+1 = [5] N 75