TH INFLUNC OF RATOON CROPPING ON SWT SORGHUM YILD, SUGAR PRODUCTION, AND INSCT DAMAG R. R. DUNCAN and W. A. GARDNR' tdepartments f Agrnmy and ntmlgy, Gergia xperiment Statin, Griffin, Ga. 30212. Received 14 JuIy 1983, accepted 22 Nv. 1983. Can. J. Plant Sci. Dwnladed frm www.nrcresearchpress.cm by 37.44.206.132 n 01/26/18 DuNcaN, R. R. an GanNsn, W. A. 1984. The influence f ratn crpping n sweet srghum yield, sugar prductin, and insect damage. Can. J. Plant Sci.64: 261-273. As multiple crpping practices cntinue t spread in the sutheastern U.S.A., ratn crpping (tw harvests frm a single planting) prvides an additinal duble-crpping scheme fr farmers. Furteen sweet srghum (Srghum biclr (L.) Mench) cultivars were evaluated in a ratn duble-crpping system at tw lcatins during 1980 and 1981. Significant cultivar x lcatin interactins were detected bth years. nvirnmental cnditins (particularly air and sil temperatures) and genetic capability gverned perfrmance f cultivars in the ratn crpping system. The Castal Plain lcatin prvided a mre stable envirnment fr ratn crpping f srghum than the Piedmnt lcatin and this prductin dependability was attributed t warm temperatures during April-May and Octber- Nvember cupled with at least 230* frst-free days. Ttal whle-plant green weights were 36V higher in the Castal Plain than in the Piedmnt. Percent sugar cncentratin was l5v higher n the first crp and 9V htgher n the ratn crp in the Piedmnt than in the Castal Plain. Calculatin f ttal sugar yield per hectare revealed that the cultivars prduced 43Va mre sugar when grwn in the Castal Plain than in the Piedmnt. Rma was the best cultivar in the Castal Plain while Brandes, Wray, and Keller were the best cultivars in the Piedmnt. MN 960 and Ramada shuld be avided when ratn crpping. Insect damage was significantly greater n the ratn crp than n the first crp. Fall armywrm (Spdptera frugiperda (J.. Smith)) larvae caused the majr fliar damage n the ratn crp. Genetic imprvements are needed in sweet srghum cultivars used in ratn crpping t increase ttal plant weight prductivity (especially n the ratn crp), sugar accumulatin in the stem (particularly n the first crp), tillering capability in the ratn crp, germinatin and seedling vigr in cl sils, and disease and insect resistance. Key wrds: Srghum biclr (L.) Mench, duble crpping, cultivar by lcatin interactin, Spdptera frugiperda (J.. Smith), Helithis zea (Bddie) [ffets de Ia culture de repusse sur le rendement, la prductin de sucre et les d6gats dus aux insectes chez le srgh sucr6.l Titre abr6g6: Rendement et r6sistance aux insectes des plants de repusse de srgh suc16. La culture multiple se gagne la faveur d'un nmbre crissant de cultivateurs du sud-est des tats-unis. Or, la culture de repusse cmpte parmi les mdes de culture duble que ces derniers peuvent chisir. Nus avns 6valu6 14 cultivars de srgh sucrd (Srghum biclr (L.) Mench) cultiv6s de cette fagn ir deux endrits diff6rents, en 1980 et en 1981. Les deux ann6es, nus avns bserv6 une interactin significative entre le cultivar chisi et I'endrit de culture. Le rendement des cultivars ainsi cultiv6s d6pendait des cnditins du milieu (ntamment la temp6rature de I'air et du sl) et des caract6ristiques g6n6tiques des plantes. La Can. J. Plant Sci. 642 261-273 (Apr. 1984) 26r
262 CANADIAN JOURNAL OF PLANT SCINC Can. J. Plant Sci. Dwnladed frm www.nrcresearchpress.cm by 37.44.206.132 n 01/26/18 plaine cdtibre ffre un milieu plus stable pur la cuiture de repusse du srgh que la r6gin de Piedmnt et la prductin supdrieure btenue au premier endrit est attribuable aux tempdratures plus chaudes enregistr6es en avril-mai et en ctbre-nvembre et d une p6ride sans gel d'au mins 230jurs. Le pids frais des plantes entidres cultiv6es dans la plaine cdtibre d6passait de 36Va celui des plantes prvenant de la r6gin de Piedmnt. Par cntre, la teneur en sucre de ces dernidres d6passait de l57 (premidre r6clte) et de 9V (repusse) celle des plantes de la plaine cdtibre. Cependant, une 6valuatin du rendement ttal en sucre par hectare a mntrd que les cultivars prduisaient 43Va de plus de sucre dans la plaine cdtibre que dans le Piedmnt. Rma 6tait le meilleur cultivar dans la plaine c6tibre tandis que Brandes, Wray et Keller dnnaient les meilleurs r6sultats dans le Piedmnt. Pur leur part, les cultivars MN 960 et Ramada ne cnviennent pas h la culture de repusse. Les d6gats caus6s par les insectes snt sensiblement plus imprtants chez les plants de repusse que chez ceux de la premibre r6clte. Les dmmages inflig6s au feuillage snt surtut dus aux larves de la l6ginnaire d'autmne (Spdprera frugiperda (J.. Smith)). Il faudra apprter des am6liratins g6n6tiques aux cultivars de srgh sucr6 utilis6s en culture de repusse pur en accritre la prductivit6 ttale (ntamment celle des plants de repusse), la teneur en sucre des tiges (surtut de la premibre r6clte), le tallage des plants de repusse, la germinatin et la vigueur des plantules en sls frids et la r6sistance aux maladies et aux insectes. Mts cl6s: Srghum biclr (L.) Mench, culture duble, interactin cultivarendrit de culture, Spdptera frugiperda (J.. Smith), Helithis zea (Bddie) Srghum (Srghum biclr (L.) Mench) is a versatile crp which can be grwn fr grain, frage, silage, sirup and/r sugar prductin. The crp can be planted ver a wide range f climatic as well as sil envirnments. Because f this versatility, srghum is readily adaptable t mst multiple crpping prgrams. Since many states in the sutheastern U.S.A. have lng grwing seasns (225+ frst-free days), multiple crpping practices are being adpted. Duble-crpping f such warmseasn crps as crn, vegetables, tbacc, and srghum is prviding increased revenue frm the same land during a single grwing seasn. Ratn crpping is an additinal duble-crpping scheme whereby the crp is harvested tw r mre times frm a single planting during the grwing seasn. Srghum can be ratn-crpped fr grain, frage, r silage (Duncan 1979, 1981, 1983; Plucknett et al. 1970). Varius agrnmic parameters invlving ratned srghum have been investigated (scalada and Plucknett 1975a,b, 1911; Prabhakar 197 6; Mlina et al. 197'7 ; Tuchtn and Martin 1981) including weed cntrl (Banks and Duncan 1983; Duncan 1981; Obrien et al. 1916). Sweet srghum can be grwn fr either sirup (Cleman 1970; Freeman et al. l9'7 3) r sugar (Bradhead 1973; Cet and Smith 1974; Sund et al. 1976) prductin in the U.S.A. In additin, sweet srghum has ptential as a primary alternate surce f renewable energy (Reeves et al. 1979; Smith and Reeves 1979, 1981). Infrmatin n the ratn capability f sweet srghum is lacking. This study investigated the influence f ratn crpping n green weight, sugar prductin, and insect damage fr several sweet srghum cultivars. MTHODS AND MATRIALS These experiments were cnducted during 1980 and 1981 at tw lcatins in Gergia: The Castal Plain regin n a Greenville sandy clay lam sil (Rhdic Paleudult) near Plains (Sumter Cunty) and the Piedmnt regin n a Cecil sandy lam sil (Typic Hapludult) near Griffin (Pike Cunty). The prductin schedule, rw
DUNCAN AND GARDNR - YILD AND INSCT DAMAG OF RATOON CROPS. SWT SORGHUM 263 Can. J. Plant Sci. Dwnladed frm www.nrcresearchpress.cm by 37.44.206.132 n 01/26/18 spacings, sil ph, and ttal amunt f irrigatin water applied fr each year and lcatin during the study are prvided in Table l. Generally, the sweet srghum was planted in early April, initially harvested by early August, and the ratn crp harvested in mid- t late Nvember. Rw spacings were 91 cm at Plains and'76 cm at Griffin. Sil ph ranged frm 6.4 at Plains t 5.8 at Griffin. Mre irrigatin water was needed fr ptimum plant grwth at Plains due t the drught-susceptible characteristics f the Greenville sil. Seeding rate was apprximately 86 500 seed per hectare at bth lcatins. Plant ppulatins at emergence were nt adjusted t unifrnr levels since the capability f the varius sweet srghum cultivars t germinate, emerge, and grw in less-than-ptimum sil temperature (<18'C) cnditins was an imprtant cnsideratin in the study. Furteen cultivars (Table 2) were planted in three-rw plts 5.2 m lng and yield, stand cunts, and refractmeter readings were taken frm the center rw nly. The experimental design was a randmized cmplete blck with three replicatins. The center rw f each three-rw plt was harvested at apprximately the sft dugh stage f develpment fr the first harvest and the sft dugh t mid-dugh stage fr the secnd harvest. Cutting height was apprximately l2 cm. Several cultivars exhibited sme variability in stage f maturity at harvest (i.e. MN 1500 had nt reached the sft dugh stage at the first harvest) and, therefre, had nt attained a peak in sugar prductin. Bimass yields were measured frm hand-harvesting and weighing f 5.2- m plts. Fertilizer applicatins n the initial and ratn crps (Table 3) were based n sil test Table l. Prductin schedrrle and agrnmic data by year fr the ratn study at Plains and Griffint Dates Year Lcatin Plant Harvest-1 Harvest-2 l 980 198 l Plains Griffin PIains Griffin 8 Apr 18 Apr 7 Apr. 8 Apr. 30 July 7 Aug 3 Aug 30 July l3 Nv. l9 Nv. 23 Nv. l9 Nv. Rw spaclng (cm) Sil ph Irrigatin (mm) lgreenville sandy clay lam sil (Rhdic Paleudult) and Cecil sandy lam sil (Typic Hapludult), respectively 91 / 91 76 6.4 5.8 6.3 5.9 Table 2. Descriptin f sweet srghum cultivars in the ratn crpping study PI n.t MN n.i Descriptin Reference t52857 r52959 t5296s 152961 1529',7 r 154814 Brandes Dale Theis Keller Ri Ramada Rma Wray 0960 I 048 1054 105 6 I 060 Germplasm lines Sirup srghums Sugar srghums Freeman (1979) Freeman (1979) Freeman (1979) Freeman (1979) Freeman (1979) Freeman (1979) 419 54 368 76 Bradhead and Cleman (1974) Bradhead and Freeman (1973) Bradhead et al. (1978a) Freeman et al. (1919) Bradhead (1972) Freeman et al. (.19'74) Freeman et al. (1972) Bradhead et al. (1978b) tplant intrductin identificatin number. tspecific number allcated t the line when it was intrduced int the sweet srghum breeding prgram at Meridian. MS (U.S.A.). MN stands fr 'Meridian.'
264 canadtan JURNAL F plant scinc Table 3. Fertihzer applicatins by year fr the primary and ratn crps at Plains and Griffin Lcatin Year Preplant (kg'har) Starterfl Pstemergence (L ha r) (kg'har) Ratn (kg'ha ') Plainsf Griffini I 980 1981 1 980 198 I 560 6-12 65 785 5-10-ls 673 s l0-15 560 5-10-15 94 10-34-0$ t96il t8-46-0 90 34-0-0s I 12 34-0-0 336 34-0-0 336 34-0-0 s6 34-0-0$ 168 34-0-0 336 34-0 0 336 34-0-0 Can. J. Plant Sci. Dwnladed frm www.nrcresearchpress.cm by 37.44.206.132 n 01/26/18 tgreenville sandy clay lam sil (Rhdic Paleudult). lcecil sandy lam sil (Typic Hapludult). $N-P2O5-K2O. flapplicatin immediately after planting. //Kilgrams per hectare applied apprximately 5 cm t the side f the seed and 5 cm deep. recmmendatins. Preplant applicatins were bradcast and incrprated. Starter fertilizer was applied at bth lcatins in 1981 t enhance early seedling grwth in a cl (<18"C) sil (Duncan 1981). Applicatins f starter fertilizer included banding (f liquid 10-34-0 (N-P-K)) ver the rw at Plains and sidedressing (f slid 18-46-0) in a 5 x 5-cm placement (apprxtmately 5 cm t the side f the seed furrw and 5 cm deep) immediately after planting at Griffin. Fertilizer amendments fr the ratn crp were applied in a band between rws n the surface and irrigatin water was applied t incrprate the nitrgen. The P and K requirements were adjusted prir t planting and sufficient quantities were applied t grw tw successrve crps. Weeds were effectively suppressed at Piains with a pstemergence applicatin f 1.68 kg/ha active ingredient (a.i.) atraztne (2-chlr- 4(ethylamin)-6-(isprpylamin) -s-triazine) and at Griffin with a preemergence applicatin f 2.20 kg/ha a.i. prpazine (2-chlr-4,6- bis(isprpylamin)-s-triazine). Weeds in the ratn crp were cntrlled with pstdirected applicatins f paraquat ll.l'-dimethyl-4.4'- bipyridinium in) at a rate f 0.56 kg/ha a.i. N insecticides were applied t the research plts at either lcatin during the study. Insects were surveyed n bth the initial and ratn crps fr damage at Griffin in 1981. Fur sweet srghum cultivars were selected fr cmparisn with tw silage-type cmmercial srghum hybrids (checks). Individual plts were sampled fr lepidpteran larvae and rated fr damage during the vegetative stage f grwth (apprximately 35 cm height). Fliar damage was visually rated (Wiseman and Davis 1979) n 2O plants per plt based n the scale 0 : n damage and Q : plant killed. Sugar determinatins were made frm 5-cm basal stem segments cllected at harvest. Five randmly selected stem segments per replicatin were placed in a plastic bag, sealed, and stred in a freezer fr apprximately I m. Sugar estimatins were made using a Bausch & Lmb hand-held refractmeter (n. l3-965- 120, 1w reading range 0 t 60V slids) based n extracted juice samples frm each basal stem segment. The sweet srghum (at the sft t middugh stage f develpment) juice cntains apprximately 957 sugars and 5Va rganic/ inrganic mineral salts (i.e. apparent ttal sluble slids in slutin). Ttal sugar prductin fr specific cultivars was calculated accrding t the fllwing frmula: grss whle-plant (green) weight in Mg'ha t x 0'70 (cnversin f grss weight t stalk weight based n previus sweet srghum variety trial data in Gergia in which stalk weights and whle plant weights have been cmpared) x 0.45 (uice extractin efficiencyt x sugar cntent (frm refractmeter reading i.e' a 76V reading wuld be 0.16 in this frmula) x 0.95 (sugar extractin efficiency) : Mg ttal sugar'ha l These calculatins prvide nly a rugh estimatin f ttal sugar prductin and values will vary with increased r decreased efficiencies in juice and/ r sugar extractin as well as higher r lwer sugar measurements. A significant cultivar x lcatin interactin was fund fr the agrnmic characteristics which were measured. Cnsequently, all data were evaluated n a per-lcatin basis. Mean air temperatures and mnthly rainfall measurements are presented in Table 4 fr Plains and Table 5 fr Griffin. Althugh the mean air temperature cmparisns ver the 2-yr study were nly 0.7"C higher at Plains than at Griffin, temperatures during the critical mnths f April-
DUNCAN AND GARDNR YILD AND INSCT DAMAG OF RATOON CROPS, SWT SORGHUM 265 Table 4. Mean air temderatures and rainfall bv mnth fr the Castal Plain lcatinf Can. J. Plant Sci. Dwnladed frm www.nrcresearchpress.cm by 37.44.206.132 n 01/26/18 Data Year Apr May June July Aug Sept 1980 16.8 l98r r9.5 1980 108 198 l 053 2l.t 25.3 20.4 26.1 89 096 68 l0l 27.8 27.8 27.2 1/ < 25.9 22.6 16.8 r6.8 046 096 76 88 108 134 11 92 t32"n latitude, 84'W lngitude, elevatin 160 m. Sumter Cunty (Plains), Ga. frainfall frm planting t ratn harvest date. mmt Table 5. Mean air temperatures and rainfall by mnth fr the Piedmnt lcatinf tz.t zl.l 12.9 21.4 Ttal 0l 600 36 603 Year Apr. May June July Oct. Mean 1980 t6.2 19.7 i981 18.3 19.4 1980 t2 t67 1981 s8 056 25.5 28.l 26.7 26.6 27.0 24.4 78 054 108 46 tt2 183 25.7 22.O 124 011 15.9 15.2 130' l6'n latitude, 84" 17'w lngitude, elevatin 282 m. Pike Cunty (near Griffin), Gergia. IRainfall frm planting t ratn harvest date. May and Octber-Nvember were cnsistently warmer at Plains. Plains and Griffin are lcated n apprximately the same lngitude (84' W) but differ by 2" in latitude. Griffin is situared 145 km nrth f Plains and is 122 m hisher in elevatin. RSULTS AND DISCUSSION Whle-plant green weights, plant height, and stand cunts at harvest fr each sweet srghum cultivar grwn in the Castal Plain regin are given in Table 6. Brandes prduced the highest whle-plant weights while Ramada prduced the lwest n the first crp. MN 1500 had the highest ratn weights and MN 960, the lwest. Cmparisn f ttal prductin (first plus ratn plant weights) values revealed that MN 1500 had the highest while MN 960 and Ramada had the lwest weights. Ratn plant weights range frm 457 (MN 960) t l42% (Ramada) f the first-crp plant weights. Mst f the cultivars prduced ratn plant weights which were 50-807 thse f the first crp. Grain hybrids were generally fund t be less efficient in prducing the ratn crp (Duncan 1979, 198 1). Ratn efficiency (R : ratn weight/ttal weight) reflects the capability 049 t2l 10. 8 21.r 11.9 20.6 Ttal 7r 723 21 608 f the specific gentype t prduce the ratn crp. A high R value indicates that a greater prprtin f the ttal weight was prduced by the ratn crp than the first crp. Ramada and Ri had the highest R values and in bth cultivars, the ratn yield exceeded the first crp yield. Hwever, ttal prductin f these tw cultivars was lw. Mst f the cultivars gave R values ranging frm 35 t 45. Idealistically, an R value f 50 means that the gentype prduced equal weights n the first and ratn crps, but this value ccurred nly with three f the cultivars (Keller, Ri, and Ramada) which were lw in ttal prductivity (except fr Keller) in cmparisn with the ther cultivars. Plant height determinatins revealed that MN 1500 and Theis were the tallest cultivars in the first crp while MN 960 was the shrtest. Fr the ratn crp, MN 1500 was the tallest and MN 1054 was the shrtest. The ratn-crp height ranged frm 75 t 9l7 f the first crp. Since equal amunts f seed (seed size was similar) were planted and germinatin rates were similar fr all cultivars, the stand cunts at harvest in the first crp re-
266 CANADIAN JOURNAL OF PLANT SCINC +F OFs r-hor-r-,c--+3= OOnON-*Nh*+rOr +l<- h ^!! S S 15::!aa\:3 \\ r-- n d--rcro-- lrr r@@*nh Can. J. Plant Sci. Dwnladed frm www.nrcresearchpress.cm by 37.44.206.132 n 01/26/18 -! 4 > F z.- il a ; a s a N F. t =tt:ti*ti "* -rr.-6\odsrr* a6+@ rs\nrhn ndoor$ -O\O-d-C r r r r6ra "i i "ti:stt \ hnrtf N$---- O O\+n@-OOnnON -NdN-dNNNdNN_N a s c-q a a 3 aa +$+-r-@$@rs @N+Odn6-O-* NNONdNONdd6ONd n+n *n6-6o-o\ 66VOO++tO+$n-n 6nOOd*O-6 n*nn +n@h r 60$$! G C A a S G C B \la-sa'qs *6! a n!-\qqq9q9\!q9 -*r@ -r--6 dd++-ooooao6 n :::::v*i.j dd c r*+-r\ sssid- idgs u= dici-;i^id<;ir6; $ t*.+s$ss- ^ ^ ^!!!!! k:f* s s s 3 tr - s t B s s-s!\ rohod nn\oo\-noo d;;.-i rrrr 9 h6nt$n ^j -jd-i -i ri ^i +. 2 S? =9 \ As i ez izz Fz7+, 6>B>>F&,>>J,&,>;, "2 il 6 5 >.:. ;try X J:: il i: B,;5 Iili Fi6 S. F y:6 ill stu ^ *a Y
DUNCAN AND GARDNR - YILD AND INSCT DAMAG OF RATOON CROPS, SWT SORGHUM 267 Can. J. Plant Sci. Dwnladed frm www.nrcresearchpress.cm by 37.44.206.132 n 01/26/18 veals the capability f the specific gentypes t germinate and emerge in a cl sil (18"C). Brandes and Dale had the greatest number f plants per plt while MN 960, Ramada, and MN 1056 had the fewest number f plants n the first crp. The stand cunt f the ratn crp ind-icates tillering capability f the cultivars and indirectly accunts fr lss f plants fllwing harvest. Keller and MN 1054 prduced the highest number f tillers in the ratn crp while MN 960 prduced the lwest. Hwever, calculatin f tillering capacity (ratn tiller number/first crp plant number) indicated that MN 960 prduced an identical plant ppulatin n the first and ratn crps. Wray was the nly cultivar t have a lwer plant ppulatin n the ratn crp than n the first crp. Brandes, Dale, and MN 1060 maintained similar plant ppulatins n the tw crps while the remaining gentypes prduced 23-74V increases in their plant ppulatins. The prductivity f the specific sweet srghum cultivars was different in the Piedmnt regin (Table 7). Whle-plant green weight cmparisns revealed that Brandes, Wray, and Keller prduced the highest weights n the first crp and MN 960, MN 1056, and Ramada prduced the lwest. Ratn plant weights varied frm a high f 31.7 Mg.ha-'fr Wray t a lw f 9.0 Mg.ha-t fr MN 960. Ttal plant weight cmparisns shwed that Wray, Brandes, and Keller had the highest weights while Ramada, MN 960, and MN 1056 had the lwest values. The ratn weights ranged frm 34 t 68V f the firstcrp weights, with the exceptin f MN 1056 (95) and Ramada (ll7%). Ratn efficiency (R) cmparisns shwed that all but three cultivars (Rma, MN 1056, and Ramada) prduced 32-367 f their ttal prductin in the ratn crp. Brandes prduced nly 23V f its ttal prductin in the ratn crp. Plant height measurements at Griffin revealed that Theis was the tallest cultivar in the first crp and MN 1056 was the shrtest. On the ratn crp, Keller was the tallest and MN 1054 was the shrtest. Height f the ratn crp was 6l-817 the height f the first crp fr mst cultivars; hwever, Wray was 6V taller and MN 1056 was l3v taller in the ratn crp than in the first crp. Keller had the highest plant ppulatin n the first and the ratn crps while MN 960 had the lwest ppulatin n bth crps. Tillering capacity cmparisns revealed that MN 1056 mre than dubled its plant ppulatin n the ratn crp ver the initial stand cunt while MN 960 and Ramada exhibited a 50V increase in the plant ppulatin. Hwever, these three gentypes had lw stand cunts n the initial crp. The plant ppulatin in MN 1060 decreased in the ratn crp. The remaining 10 cultivars increased ratn tiller ppulatins frm 4-22V ver the initial ppulatin. Brandes maintained identical ppulatins fr bth crps. The cultivars were rated fr their ability t grw in lessthan-ptimum sil cnditins (<18'C) fr germinatin and early seedling grwth during April at the Piedmnt lcatin. Keller was the best cultivar fllwed by Dale and Ri, MN 1500, Wray, and Brandes. The remaining cultivars were slw t germinate and seedling vigr was extremely pr. Percent sugar cmparisns between Plains and Griffin are presented in Table 8 fr each cultivar. At Plains, Rma and Ri prduced the highest percent sugar while Brandes and MN 1500 prduced the lwest fr the first crp. N significant differences were fund fr sugar cncentratin n the ratn crp; hwever, the percent sugar (acrss cultivars) was 37V higher fr the ratn crp than fr the initial crp. The same trend was bserved at Griffin where the mean percent sugar cncentratin f the ratn crp exceeded the cncentratin f the initial crp by 29V. Rma prduced the highest sugar value while MN 1500 had the lwest n bth crps. Dale
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210 CANADIAN JOURNAL OF PLANT SCINC Can. J. Plant Sci. Dwnladed frm www.nrcresearchpress.cm by 37.44.206.132 n 01/26/18 and Theis als had lw values in the ratn crp. Ttal sugar prductivity (which invlves green weight, percent sugar cncentratin, and cnversin factrs fr grss-t-stalk weight, juice extractin, and sugar extractin) is an imprtant cnsideratin fr sweet srghum prductin, regardless f whether the bjective is sugar, sirup, r alchl prducts. Sugar prductin values were calculated fr each cultivar and are shwn in Table 8. The calculated yields f sugar at Plains ranged frm 0.82 (Ramada) t 2.12 (Rma) Mg'ha ' n the first crp and frm 0.51 (MN 960) t 2.72 (MN 1500) Mg'ha-r n the ratn crp. Mean values acrss cultivars fr the tw crps were similar at the Castal Plain lcatin. Rma prduced the highest ttal sugar yield and MN 960 prduced the lwest. Sugar yields at Griffin ranged frm 0.50 (Ramada) t 2.19 (Wray) Mg'ha ' n the first crp and frm 0.46 (MN 960) t 1.56 (Wray) Mg'ha-l n the ratn crp. Mean values acrss cultivars were 0.50 Mg' ha-i higher fr the initial crp than fr the ratn crp. Wray prduced the highest ttal sugar yield while MN 960, MN 1056, and Ramada had the lwest prductin. Sugar prductin values acrss cultivars were 0.36 Mg'ha-' higher at Plains than at Griffin fr the initial crp, and values fr Plains were 0.83 Mg'ha t higher fr the ratn crp than fr Griffin. Cnsequently, ttal ratn duble-crpping sugar yield at Griffin was I. l9 Mg'ha- t less than at Plains. Ttal sugar prductin expectatins culd be increased by imprvement in juice extractin efficiency. The 0.45 cnversin factr used in Table 8 is based n efficiency frm a single pass thrugh a rller mill press. If the stalks were squeezed a secnd time (pssibly with increased external pressure plus the additin f water), a 0.95 juice extractin efficiency is pssible which wuld increase ttal sugar prductin. Tw species f phytphagus lepidpteran larvae were fund feeding n the vegetative-stage fliage f sweet srghum (Table 9). Crn earwrm (Helithis zea Bddie)) was fund n the first crp. Fliar damage ratings and number f crn earwrm larvae were nt significantly different amng cultivars. Fall armywrm (Spdpterafrugiperda (J.. Smith)) was fund n the ratn crp. Wray had the highest damage rating while Theis had the Table 9. Cmparisn f fliar damage ratings and lepidpteran larvae cunts fr selected sweet srghum cultivars n the initial and ratn crps during 1981 in the Piedmnt regin Variety Brandes Theis Keller Wray Checks Cnlee NRG Richardsn Sugar-red Visual fliar damage ratrng r 1.2a r.5a l.4a.la l.3a l.0a First crp N. CWI larvae/10 plants 0a la za Oa 0a 0a Visual fliar damage ratlng Ratn crp N. FAW$ larvae/ I 0 plants tratingswerebasedna0tgscale,with0:ndamageandg:plantkilledaccrdingtwisemanand Davis (19?9). Ratings were taken during the vegetative grwth stage between panicle initiatin and prebt. +CW : crn earwrm (Helithis zea (Bddie)). $FAW : fall armywrm (Spdptera;frugiperda (J.. Smith)). c-c Mean separatins are within clumns accrding t Duncan's multiple range test at the 5V level f significance. 3.2b z. lc i.-td 3.8a 3.5ab 5. ZO 11.2a 0r -3b 10.0a 09-3a 08.0a 06.2a
DUNCAN AND GARDNR - YILD AND INSCT DAMAG OF RATOON CROPS. SWT SORGHUM 27I Can. J. Plant Sci. Dwnladed frm www.nrcresearchpress.cm by 37.44.206.132 n 01/26/18 lwest. In additin, number f FAW larvae was significantly lwer fr Theis than fr the ther cultivars. When insect cunts and damage ratings were cmbined acrss cultivars, highly significant differences were detected between the initial crp and the ratn crp (Table 10). Crn earwrm larvae were fund slely n the first crp while fall armywrm larvae were damaging nly the ratn crp. Damage ratings were higher n the ratn crp than n the first crp. This same pattern f damage was bserved n srghum ratned fr grain (Gardner and Duncan 1983). CONCLUSIONS Ratn crpping f sweet srghum is an additinal duble-crpping ptin fr farmers in the sutheastern U.S.A. and in areas with similar climatic and edaphic envirnmental cnditins. Prper management is the key t success in this prductin prgram. Climatic cnditins (particularly air and sil temperatures during April-May and Octber-Nvember) are extremely imprtant and will gvern the level f prductivity f the specific cultivars. In general, the Piedmnt lcatin (Griffin) had mean air temperatures which were 1-2C cler in the early spring and fall than the Castal Plain lcatin (plains). Griffin averages abut 227 frst-free days per year while Plains averages 232 days (Duncan l98l). Since mst sweet srghum cultivars require apprximately I 30-- I 35 days frm planting t harvest fr ne crp, ratn crpping seems, at best, a marginal prductin scheme. Hwever, the ratn crp gains 2-3 wk ver replanting because the ratn crp begins immediately frm buds n plant stubs which have an established rt system. The first crp shuld have abut 120 days frm planting t harvest while the ratn crp needs 110-120 days and will usually be terminated by freezing temperatures. The Piedmnt lcatin has nt cnsistently prvided an envirnment fr successful ratn crpping f srghum due t late spring and early fall frsts. The srghum ratn research prgram in the Piedmnt has been successful apprximately 50V f the time while the upper Castal Plains has been 1007 successful fr ratn duble-crpping. Results frm this study shwed a significant gentype X lcatin interactin fr mst f the characteristics invlved in ratn duble-crpping, i.e. plant weight, height, and sugar prductin. Sweet srghum cultivars apparently differ in their adaptability fr ratn crpping. Grain srghum hybrids (Duncan 1979, l98l) as well as parental lines (Duncan et al. 1980) have previusly been fund t exhibit genetic differences when ratned. At Plains, Brandes and MN 1500 prduced high ttal green plant weights but had lw sugar cncentratins. Rma had a lwer ttal green plant weight, but a higher sugar cncentratin in the stem. Cnsequently, ttal calculated sugar prductin was highest fr Rma. MN 960 Table 10. Cmparisn f lepidpteran larvae cunts and fliar damage ratings acrss cultivars fr the initial and ratn crps during l98l in the piedmnt regin Crp N. CW/10 plantst N. FAWi l0 plantsf Fliar damage ratingsg First 0.5. 1.2 Ratn 0.0 7.8 3.2 x*{ ++ ** 1CW : crn earwrm. +FAW : fall armywrm. $Visual rating where 0 : n damage and 9 : plant killed accrding t Wiseman and Davis (1979). Ratings were taken between panicle initiatin and the prebt stage f develpment. tl/mean separatins are within clumns a"crding t single degree f freedm cmparisns between the first and ratn crps as indicated by the F test (0.01).
2'72 CANADIAN JOURNAL OF PLANT SCINC Can. J. Plant Sci. Dwnladed frm www.nrcresearchpress.cm by 37.44.206.132 n 01/26/18 and Ramada shuld nt be ratn-crpped at Plains. At Griffin, Brandes, Wray, and Keller prduced high ttal green plant weights and percent sugar values were near the mean average fr lcatin. Rma had a lw ttal green plant weight, but had the highest percent sugar cncentratin in the stem. Wray was calculated t have the highest ttal sugar prductin fllwed by Keller and Brandes. MN 960, Ramada, and MN 1056 shuld nt be ratn-crpped at Griffin. The best cultivars fr this dublecrpping prgram at Griffin wuld include Wray, Keller, Brandes, Dale, Ri, and MN 1500. Phytphagus lepidpteran larvae may require remedial cntrl treatments, especially fr the ratn crp. Larvae f crn earwrm and fall armywrm tend t burrw int and feed within the whrl f vegetative-stage srghum plants, thus making insecticidal cntrl difficult. Repeated applicatins f a txicant r utilizatin f high vlumes f carrier (465-560 L'ha ') are recmmended t btain satisfactry cntrl (Yung 1979). Hwever, ecnmic threshlds fr these pests n sweet srghum are undefined. Martin et al. (1980) established a threshld f ne larva per plant fr grain srghum hybrids, but this level appears inadequate fr ratned grain srghum (Tuchtn and Martin 1981) and may nt be satisfactry fr ecnmic cntrl f these larvae n sweet srghum. SUMMARY Sweet srghum cultivars can be ratn duble-crpped. Hwever, this study addressed nly the agrnmic and nt the ecnmic feasibility f such a prductin scheme. Since apprximately ne-furth f the cst f a sweet srghum crp is incurred prir t harvest and the remaining three-furths are invlved in harvesting and prcessing t the final prduct, ttal bimass and sugar prductin per hectare must be high enugh t justify tw harvests in cmparisn with a single crp. As with all sugar-accumulating crps, sweet srghum has a grwth (vegetative) phase fllwed by an accumulatin (reprductive) phase. An early harvest (as exemplified by the first harvest in this study) in rder t attain tw successive crps may prvide a reasnable bimass prductin, but culd sacrifice ptential sugar prductin. In additin, the secnd harvest resulted in lw bimass prductin and high sugar accumulatin. cnmic cnsideratins in cmmercial prductin f sweet srghum wuld prbably necessitate bth high bimass and high sugar prductin frm bth crps t justify ratn crpping in cmparisn with a well-managed single crp. These cmparisns are essential befre any judgments n the actual value f ratn crpping f sweet srghum can be made. Several assumptins were made when calculating ttal sugar prductin. The 0.70 cnversin factr fr estimating stalk prductin frm ttal whle-plant green weights is an apprximate figure fr mature sweet srghum. The value can vary widely amng cultivars and culd have been lwer fr the immature srghum in the study, particularly n the first crp. Similarly, the cnversin f refractmeter readings t percent sugar in the juice extracts may have been quite variable fr immature sweet srghum. The rati f nnsugar slids t sugars decreases with maturity, i.e. the purity increases. Cnsequently, the calculatins wuld prvide nly very rugh estimatins f ttal sugar prductin fr the immature sweet srghum cultivars, such as MN 1500, and may nt reflect prductin ptential. In additin, the sugar readings may have been cnservative estimates f the actual sugar cncentratin in the plant since the sugar cntent is frequently lwer in the basal interndes f the stalk in cmparisn t the upper interndes during reprductive grwth stages. A cmbinatin f plant characteristics is essential t maximize sweet srghum ra-
DUNCAN AND GARDNR - YILD AND INSCT DAMAG OF RATOON CROPS, SWT SORGHUM 273 Can. J. Plant Sci. Dwnladed frm www.nrcresearchpress.cm by 37.44.206.132 n 01/26/18 tn duble-crpping prductin with existing cultivars: cl sil germinatin and seedling vigr prduce 60-80 Mg.ha I green weight n the first crp, and 50-60 Mg'h3-t green weight n the ratn crp, prduce and maintain sufficient tillers (plant ppulatin) n the ratn crp, imprve disease resistance (Fusarium spp. and anthracnse, incited by Cllettrichum graminicla (Ces.) G. W. Wils.), prduce percent sugar levels abve I 17 n the first crp and abve 15V n the ratn crp, and ability t withstand peridic cl envirnmental cnditins during the fall mnths withut an adverse effect n grwth and develpment. Genetic manipulatin f these characteristics culd imrve verall perfrmance f sweet srghum cultivars and lead t mre stable first-crp and ratn crp bimass prductin and sugar accumulatin. These maniulatins culd expand the gegraphic area fr dependable ratn duble-crpping f sweet srghum. BANKS, P. A. and DUNCAN, R. R. 1983. Weed cntrl evaluatins in ratn-crpped grain srghum lsrghum biclr (L.) Menchl. Weed Sci. 31.254-258. BROADHAD, D. M. 1972. Registrarin f Ri sweet srghum (Reg. N. 113). Crp Sci. 12: '7 16. BROADHAD. D. M. 1973. ffects f deheading n stalk yield and juice quality f Ri sweet srghum. Crp Sci. 13: 395-396. BROADHAD, D. M. and COLMAN, O. H. 1974. Registratin f Brandes sweet srghum (Reg. N. 116). Crp Sci. 14: 494. BROADHAD, D. M. and FRMAN, K. C. 1973. Registratin f Dale sweet srghum (Reg. N. 114). Crp Sci. 13: 776. BROADHAD, D. M., FRMAN, K, C., COLMAN, O. H. and ZUMMO, N. 1978a. Registratin f Theis sweet srghum (Reg. N. 117). Crp Sci. 18: 165. BROADHAD, D. M., FRMAN, K. C. and ZUMMO, N. 1978b. Wray, a new variety f sweet srghum fr sugar prductin. Miss. Agric. Fr. xp. Sta. Res. Highlights 41(8). COTO, J. A. and SMITH, B. A. 1974. Factry scale tests f sugar prductin frm sweet srghums in Mexic. Prc. Int. Sc. Sugarcane Technl. 3:1356-1362. COLMAN, O. H. 1970. Syrup and sugar frm sweet srghum. Pages 416-440 in J. S. Wall and W. M. Rss, eds. Srghum prductin and utilizatin. Avi Publishing C., Inc. Westprt, Cnn. DUNCAN, R. R. 1979. Cmparative grain yield relatinships f three maturity grups f srghum hybrids under ratn crpping. Cereal Res. Cmmun. 7: 27-32 DUNCAN, R. R. (ed.) 1981. Ratn crpping f srghum fr grain in the sutheastern United States. Gergia Agric. xp. Sta. Res. Bull. 269. DUNCAN, R. R. 1983. Ratn crpping f srghum: an alternative multiple crpping scheme. Crps Siis 35: 10-11. DUNCAN, R. R., MILLR, F. R. and BOCK- HOLT, A. J. 1980. Inheritance f tiller regrwth in ratned srghum. Can. J. Plant Sci. 60:4'73-4'78. SCALADA, R. G. and PLUCKNTT, D. L. 1975a. Ratn crpping f srghum. I. Origin, time f appearance, and fate f tillers. Agrn. J. 67: 473418. SCALADA, R. G. and PLUCKNTT, D. L. 1975b. Ratn crpping f srghum. II. ffect f daylength and temperature n tillering and plant develpment. Agrn. J. 67: 4'79-484. SCALADA, R. G. and PLUCKNTT, D. L. 1977. Ratn crpping f srghum. IIL ffect f nitrgen and cutting height n ratn perfrmance. Agrn. I. 69: 341-346. FRMAN, K. C. 1979. Germplasm release f sweet srghum lines with resistance t dwny mildew, leaf anthracnse and rust with adequate cmbining ability t prduce prgeny with agrnmic characters acceptable fr cmmercial sirup and/r sugar prductin. Miss. Agric. Fr. xp. Sta. Res. Rep.4(2). FRMAN, K. C., COWLY, W. R., RO- SNOW, D. T., SMITH, B. A., BROAD- HAD, D. M., ZUMMO, N. and COLMAN, O. H. 1972. Rma, a new variety f sweet srghum fr ptential sugar prductin in Texas. Texas A&M Univ. L-1031. FRMAN, K. C., BROADHAD, D. M. and ZUMMO, N. 1973. Culture f sweet srghum fr sirup prductin. ARS-USDA Agric. Handbk. n. 441, Washingtn, D.C. FRMAN, K. C., COWLY, W. R., RO- SNOW, D. T., SMITH, B. A., ZUMMO, N., RYS, L., BROADHAD, D. M. and SUND, K. A. 1974. Ramada, a new variety f sweet srghum fr ptential sugar prductin in
2'74 CANADIAN JOURNAL OF PLANT SCINC Can. J. Plant Sci. Dwnladed frm www.nrcresearchpress.cm by 37.44.206.132 n 01/26/18 Texas. ARS-S-41, Suthern Regin, USDA. FRMAN, K. C., BROADHAD, D. M. and ZUMMO, N. 1979. Keller, a new high-sucrse sweet srghum with ptential fr sugar prductin. Miss. Agric. Fr. xp. Sta. Res. Rep. 4(8). GARDNR, W. A. and DUNCAN, R. R. 1983. ffects f planting date and ratn crpping n the natural incidence f selected insect pests f grain srghum in central Gergia. J. Ga. ntml. Sc. 18: 327-335. MARTIN, P. B., WISMAN, B. R. and LYNCH. R.. 1980. Actin threshlds fr fall armywrm n grain srghum and cstal bermudagrass. Fla. ntml. 63: 3'75-405. MOLINA, A. B., Jr., CABANGBANG, R. P. and QUINTANA, R. V. 1977. Ratn perfrmance f selected grain srghum varieties at three levels f plant ppulatin and nitrgen fertilizatin. Philippine J. Crp Sci. 2: 109-125. OBRIN, S. R., PLUCKNTT, D. L., de la PNA, R. S. and SCALADA, R. G. 1976. Chemical weed cntrl in a ratn crpping system fr srghum. InPrc.5th Asian-Pacific Weed Sci. Sc. Cnf., Tky, Japan. pp. 334-338. PLUCKNTT, D. L., VNSON, J. P. and SANFORD, W. G. 1970. Ratn crpping. Adv. Agrn. 22: 285-330. PRABHAKAR, M. 1976. Agrnmic investigatins n ratning f srghum [Srghum biclr (L.) Menchl. Mysre J. Agric. Sci. 10: 716. RVS, S. A., Jr., HIPP, B. W. and SMITH, B. A. 1979. Sweet srghum bimass. I. Agrnmic data. Sugar y Azucar 74: 23-30. SMITH, B. A. and RVS, S. A., Jr. 1979. Sweet srghum bimass. IL Plant cmpsitin. Sugar y Azucar 74:3V35. SMITH, B. A. and RVS, S. A., Jr. 1981. Sweet srghum bimass. III. Cultivars and plant cnstituents. Sugar y Azucar 76:-37-50. SUND, K. A., COWLY, W. R., SMITH, B. A. and FRMAN, K. C. 19'76. Sweet srghum varieties fr sugar prductin in Suth Texas. Sugar J. 39:4143. TOUCHTON, J. T. and MARTIN, P. B. 1981' Nitrgen and insecticide applicatins fr ratning grain srghum. Agrn. J. 73: 298-300. WISMAN, B. R. and DAVIS, F. M. 1979. Plant resistance t the fall armywrm. Fla. ntml. 62: 123-130. YOUNG, J. R. 1979. Fall armywrm: cntrl with insecticide. Fla. ntml.62: 731-133. YOUNG, J. R. 1979. Fall armywrm:cntrl with insecticide. Fla. ntml. 62: 131-133'