PRELIMINARY INVESTIGATIONS INTO THE COMPETITIVE EFFECTS AND CONTROL OF CYPERUS ROTUNDUS L. IN SUGARCANE FIELDS

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1 Proceedings of The South Afrcan Sugar Technologists'kssociation June PRELMNARY NVESTGATONS NTO THE COMPETTVE EFFECTS AND CONTROL OF CYPERUS ROTUNDUS L. N SUGARCANE FELDS ' By P. E. T. TURNER South African Sugar Association Experient Station, Mount Edgecobe, Natal Abstract Preliinary results of four experients designed to deterine the copetitive effects of Cyperus rotundus L. on sugarcane and to investigate ethods of controlling this weed, are reported. A trial in which a plant crop of varieties N13 and N8 was grown under rainfed conditions showed that copetition fro C. rotundus caused decreases in yield of 85 and 83% respectively. n a second trial under irrigation, stalk elongation and tillering were slower in plots of plant cane which contained C. rotundus. Methods of reestablishing sugarcane which showed effective control of C. rotundus include: iniu tillage with a second application of glyphosate (Roundup), conventional tillage with a single or repeated application of Roundup onto eerged C. rotundus plants; and to a lesser extent, the use of Epta Super at the tie of planting. Two trials in ratoon cane showed that any treatents provide short ter control of C. rotundus populations, even in the following ratoon. The best treatents were repeated applications of Roundup, hexazinone (Velpar) and MSMA, and hand hoeing. The growth of ratoon sugarcane was not iproved by controlling C. rotundus, but no treatent eliinated C. rotundus copletely. Crop growth will be onitored in subsequent ratoons to assess the effect of reduced C. rotundus populations. ntroduction Cyperus rotundus L. (purple nutsedge) is a weed of soe 52 crops in 92 countries and is regarded as the world's worst weed (Hol et a13). n South Africa it occurs in heavy and light soils in both the northern irrigated areas and the war coastal rainfed areas where 1% ground cover is coon. A nuber of crops are affected by the severe copetition of this weed (Hol et al;' Meissner et a14) and in sugarcane, decreases in yield of 75% in Argentina and 38% in Australia (even with cultivation) have been reported (Hol et a13). Large reductions in yield caused by the weed have been reported fro Mauriti~s.~ The results of research in South Africa suggested that good control of eerged C. rotundus plants could be achieved with 2,4D and paraquat (Gosnell& Thopson2) and preeergence control could be achieved with EPTC (Epta Super) and butylate in plant cane (Thopson & G~snell;~ Turner7). C. rotundus was however not eradicated and relatively high rates of 2,4D ($3 kg ae/ha) were required for acceptable control. The ~uose of the four ex~erients re~orted here was to deterheihe copetitive effe'cts of the weed on the plant crop of varieties N13 and N8 grown on a weak sandy soil with rainfall only and on the plant crop of variety NCo 376 grown under irrigation on a sandy loa soil. Various ethods of controlling the weed were evaluated by deterining their effects on the yields of ratoon crops of variety N8 on a coastal sandy soil and variety N52/219 under irrigation on a sandy loa soil. Experiental Procedure Details of the site, soil type, variety, crop and rainfall are presented in Table 1. A randoised block design with one to six replications was used in all experients. The gross size of the plots used in experients to easure the effects of copetition in plant cane, ranged fro four rows 16 long to four rows 6 long. The three or four interrow areas used for the weed control experients were 4 long. The two outer rows and one etre fro each end of the reaining rows were discarded at the tie of harvesting in the experients designed to study the effects of weed copetition on crop yield. For coparison, an unsprayed control strip at least one etre wide was left at the end of every plot in the weed control experients. n all four experients, a leveroperated knapsack sprayer fitted with an APM Green Albuz floodjet was used. The nozzle was held between the cane rows except when glyphosate (Roundup) was used to kill sugarcane or C. rotundus, when the spray was directed over the cane or C. rotundus. ediately after Epta Super was applied, tractordrawn or hand held otorised rotary hoes were used to incorporate the product into the soil. Weed control was assessed either by visual ratings of percent control relative to unsprayed areas, or by eans of saple counts of C, rotundus plants in a 2 X 2 area. Where subterranean parts of plants were counted, the size of the saple was 2 X 2 X 15. Crop growth was easured regularly in all experients. height was easured fro ground level to the top visible dewlap of 2 randoly selected stalks in each plot and the stalks in one net row of each plot were counted. Where the cane was harvested and weighed, a saple of 12 stalks was taken fro each plot for sucrose analysis. TABLE 1 Experient details Experient No. 1 A 1 B Site Udloti : Natal Estates Udloti : Natal Estates Hluhluwe : Glen Park Ests Mt Edgecornbe : Natal Estates Hluhluwe : Glen Park Ests Series Clansthal Clansthal Oakleaf Fernwood Oakleaf Soil type Clay O/o Variety N13 N8 NCo 376 N8 N52/219 Crop Ratoon Ratoon rrigated or rainfed Rainfed Rainfed gated Rainfed rrigated Rainfall Oh of LTM* 63 Total rainfall plus igation () Up to 5,5 ths 561 * LTM = long ter ean

2 144 Proceedings of The South African Sugar Technologists' Association June 1984 Experient 1A and 1B The site at Udloti had been treated with glyphosate to reove Cynodon dactylon which had died and the area becae infested with C. rotundus. n Experient 1A variety N13 was used and the treatents were: 1. C, rotundus plants and tubers were left to grow and copete with sugarcane. 2. C. rotundus plants and tubers reoved to a depth of 15 by sieving the soil. n Experient 1B with variety N8, 1. C. rotundus plants were left to grow and copete with sugarcane. 2. C. rotundus plants were treated three ties with Roundup prior to planting. n the 'no C. rotundus' plots, any plants which gerinated subsequently were reoved by hand. All plots were treated with alachlor (Lasso) plus atrazine at planting to control grass and broadleaf weeds and any subsequent grass and broadleaf weeds which grew were reoved by hand. The soil in 'C. rotundus' plots was disturbed with hand hoes to siulate the sieving operation in the 'no C. rotundus' plots in case disturbing the soil reduced the daage to cane by parasitic neatodes. The neaticide aldicarb was applied to all plots. Furrows were drawn and planting was done by hand. Cane setts were planted endtoend in a double row at a depth of approxiately 1. Experient 2 are shown in Table 2. The young ratoon crop on the site of the experient was infested with C. rotundus to which a herbicide ixture based on paraquat had been applied once. All the cane on the site was cut back and the cane in the plots for the iniu tillage treatent was left to grow. The other plots were ploughed as indicated in the table of treatents. C. rotundus grew again and was dense in the iniu tillage plots; ing was done by hand after ridgg with a three furrow tractordrawn ridger. Standard Fertilizer Advisory Service analytical data were used for deterining the fertilizer requireents. The plots consisted of four rows 32 long; half of each row was treated to control C. rotundus and the other half was not treated. Two saple areas each consisting of two 6 long rows in each subplot were used for easuring crop growth and assessing the population of C. rotundus. Experient 3 are listed in Table 3. 1 (oxynil + 2, 4D) 2 MCPA + surfactant (S) 3 MCPA + S 4 Aetryne + (ioxynil + 2, 4D) 5 Aetryne + MSMA 6 Aetryne + MSMA 7 (oxynil + 2, 4D) 8 MSMA 9 MCPA + paraquat 1 Hexazinonelhexazinone 11 Hexazinoneldiuron + (ioxynil + 2, 4D) 12 Diuron + (ioxynil + 2,4 D) (repeated) 13 Hexazinonelhexazinone 14 Glyphosate (Roundup) TABLE 3 used in Experient 3 Rate in kg or P ai or aelha 1, , , ,44, ,88 2,88 1,6 +,6,675/,54,67512,O +,875 2, +,875/2, +,875,3381,338 1% solution Coents Single applications on 25 October Split applications on 16 Septeber and Applied with a brush Control : Plough (C. rotundus left to copete) Treated : Plough + Roundup on C. rotundus (1 application) Treated : Plough + RoundGp on C. rotundus (2 applications) Control : Plough (C. rotundus left to copete) Treated : Plough + Epta Super at planting Control : Plough (C. rotundus left to copete) Treated : Plough + Dual + aetryne + paraquat Control : Min, tillage1 Wup application (C. rot. left to copete) Treated : Min. tillage1 Wup application + Epta Super on row Control : Min. tillage2 Wup applications (C. rot. left to copete) Treated : Min. tillage2 Wup applications + Epta Super on row TABLE 2 reatents used in Experient 2 No. of subplots Weed control prograe Dual + aetryne + paraquatldiuron + 1 (ioxynil + 2, 4D) Diuron + (ioxynil + 2, 4D)(2 applications) Diuron + (ixoynil + 2, 4D) (2 applications) Diuron + (ioxynil + 2, 4D)(2 applications) Diuron + (ioxynil + 2, 4D) (2 applications) Tillage procedure No soil disturbance after Roundup application. Ridged directly into soil Rotary hoe for incorporation into soil Notes on treatents: 1. All furrows in plots were drawn by a three furrow tractordrawn ridger body. 2. Plough treatent consisted of a cross ripping (in two directions) and two subsequent discing operations except in treatent A which had only one discing operation. 3. Regrowth of C, rotundus was extensive where Roundup had been applied so another 6 Uha was applied to one plot of each treatent. 4. Where Epta Super was used in iniu tillage plots, fiu~ows for planting did not always follow through the treated area only. A hand held otorised rotary hoe was used to incorporate the herbicide into the soil. 5. Where Epta Super was used in ploughed plots, a tractordrawn rotary hoe was effective in incorporating the herbicide into the soil and also produced an extreely fine soil tilth. No soil disturbance nrow incorporation only No soil disturbance nrow incorporation only

3 Proceedings of The South African Sugar Technologists' Association June A ratoon crop of variety N8 was growing on the weak sandy soil of this site in which the infestation of C. rotundus was very heavy. were applied on three occasions and rainfall received during these periods is given in Table 4. TABLE 4 Weather conditions during and after spraying on three dates 16 Septeber October Noveber ,O 46 Rainfall () 6 Sunshine All weeds other than C. rotundus were reoved by hand. C. rotundus populations above and below the ground and the growth of the crop were assessed at intervals after treatent. Then (seven onths after the first treatent) the plots in which the two treatents were ost effective, were sapled and the viability of the tubers tested by replanting the in pots and watering the. Tubers fro two soil saples (2 X 2 X 15 ) fro each treatent were used and the nuber of tubers which subsequently gerinated were counted. Experient 4 are listed in Table ,6 1,6 3,4 15,8 5,9,4 1,O 68 TABLE 6 TABLE 5 used in Ex~erient 4 Ex~lanation 1 Untreated 2 Hand hoe repeatedly 3 Aetryne + (ioxynil + 2, 4 D) repeated 4 Alachlor + 2, 4D + paraquat followed by aetryne + (ioxynil + 2, 4D) 5 MSMA repeated " 6 Glyphosate repeated A ratoon crop of variety N52/219 was harvested at the end of October 1982 and the field was used for this experient. were applied between the cane rows to control as any C. rotundus plants as possible. n treatent 6 Roundup was applied to plants in the interrow only so that the cane crop was not daaged. The degree of control of C. rotundus was assessed prior to the foration of the leaf canopy and after harvesting, any residual effects were exained. Crop growth was easured throughout the growing period and will be continued in subsequent ratoons to try to deterine whether there will be any benefit in crop growth due to the residual control of C. rotundus. Experient 1. C. rotundus control To allow full C. rotundus copetition Conducted four ties at 23,5 week intervals to siulate echanical cultivation Conducted on interrow plants only Repeated twice. Rates ai/ha = 1,75 +,77 Rates ai/ha = 1,99 + 1,22 +,26 and 1,75 +,77 respectively Repeated twice. Rates ai/ha = 2,52 Repeated three ties. Rates 1% solution Applied with nylon brush and wiped onto interrow weeds only nrow weeds reoved by hand pulling Results C. rotundus plant and tuber populations at the tie of planting or spraying glyphosate and shortly before and after harvesting on 3 Septeber Experient la Experient 1B plant T~bers~' C. rotundus No C. rotund '1' 1 ' ]3* '1: C, rotundus 8 Aug ' No C. rotundus [ length C. rotundus 1 population No C. rotundus * and tuber populations before spray were eans of saples fro all plots 1,o 1 r2 spray... s2. 8 Aug C. rotundus [ length No C. rotundus spray C. rotundus population No C. rotundus.+*4==",.* *** /*.\, *.* '...*. //, '\ /+ //, p** L ',, T~bers~',/ Z \ ',*<...._ Crop age (days) Crop age (days) FGURE 1 Effect of treatents on length and population of stalks in Experient 1 A FGURE 2 Effect of treatents on length and population of stalks in Experient 1 B.

4 146 proceedings of The South ;frican Sugar Technologists' Association June 1984 sieving the top 15 A of soil was effective in reducing the nuber of C. rotundus plants but they were not eliinated copletely. Roundup applications in Experient 1B were less effective in controlling C. rotundus and spot spraying was necessary on two occasions after the initial treatent. Population counts after harvesting indicate the degree of control achieved. Crop growth Gerination of cane was slower in plots with C. rotundus and the production of tillers was retarded in both varieties. The differences between the effects of treatents on the nuber and length of stalks were obvious throughout the growth period of the crop. Variations in stalk population can be attributed partly to daage caused by terites in plots of both treatents. Yield data Yields were low even where there was no C. rotundus. The cane yielded 2,9 tons per hectare per onth in Experient 1A and 2,7 tons per hectare per onth in Experient 1B. These yields were however reduced by 83 and 85% respectively as a result of copetition fro C. rotundus. The effect of the weed ay have been exacerbated by stress because the crop received only % of the average rainfall during its growth period. Experient 2 C. rotundus control C. rotundus was well controlled only by treatents which included glyphosate. Two applications of glyphosate were ore effective than a single application to newly eerged C. rotundus both after ploughing, and particularly in the iniun tillage plots. This could have been because cbverage of C. rotundus plants in the interrow was poorer when sprays were directed over the cane row. Other reasons could have been the length of tie between the h t spray and planting and the fact that not all the tubers had gerinated when the plot was first treated. Crop growth C. rotundur No C. rotundus CV % 1 Cane tha 5,3* 3,7 45 Yield Suc % cane 11,35 12,65 1 = Plough 2 = Plough t 1 Roundup spray 3 = Plough 4 = Plough + 2 Roundup sprays 5 = Plough 6 = Plough + Epta Super 7 = Plough 8 = Plough + Dual + aetryne + paraquat 9 = Miniu tillage (1 Roundup spray) 1 = Miniu tillage t Epta Super (1 Roundup spray) 11 = Miniu tillage (2 Roundup sprays) 12 = Miniu tillage t Epta Super (2 Roundup sprays) FGURE 3 C. rotunduspopulations: ean of counts on three sapling dates. $9 Experient 1A (N13) Suc tha,66* 3,94 TABLE 7 Harvest results, Experient 1 length (),57**,94 * statistically siificant at the 5% level ** Statistically significant at the 1% level ul N length irnl 5 F 8 o E ul.8 C n Ot d.6 Ln 7 5 P.5 21,B.4 o E F c 1, i? 2 $.2 e P tj $,l 47,8 3,9 popn. (loockha) i Cane tha 3,82** 25,O 17,6 Yield Suc % cane 1,2 1,97 62 Experient 1B (N8) Suc tha,4** 2,74 19,O length ( 4,54** 1,55 1, = Plough 2 = Plough t 1 Roundup spray 3= Plough 4 = Plough + 2 Roundup sprays 5= Plough 6 = Plough + Epta Super 7 = Plough 8 = Plough t Dual + aetryne + paraquat 9= Miniu tillage (1 Roundup spray) 1= Miniu tillage t Epta Super (1 Roundup spray) 11 = Miniu tillage (2 Roundup sprays) 12 = Miniu tillage t Epta Super (2 Roundup sprays) FGURE 4 Crop easureents at 5,5 onths of age. popn. (1 OOCkha) 37** ,l : Y G

5 Proceedings of The South African Sugar Technologists' Association June After $5 onths, there were arked differences between treatents in the length and population of cane stalks. s were generally longer where glyphosate had been applied to C. rotundus or in the iniu tillage syste where only the repeat application resulted in a arked iproveent. Applications of Epta Super in conventionally tilled plots resulted in longer stalks but had a detriental effect on cane growth in iniu tillage plots where glyphosate was applied twice. s in plots which had been treated with Dual plus aetryne plus paraquat were only slightly longer than those in the unsprayed plots.. C. rotundus infestation and crop growth xx population a x +.A length C. rotundus population (1/2) FGURE 5 Relationship between C. rotundus population and (1) length and (2) population of stalks. Generally, the level of control of C. rotundus was unacceptable coercially, although all treatents provided soe easure of control for at least one.onth. Horone ixtures provided soe control while the effect of MSMA ixtures was very shortlived. Repeated treatents of hexazinone or glyphosate provided the best control and a arked reduction in the nuber of C. rotundus plants was apparent in these treatents in February, three onths after the second application. A saple taken in February showed that there were no fewer tubers after the treatents but their viability had been affected. Gerination of tubers fro plots treated with glyphosate and hexazinone, expressed as a percentage of gerination of tubers fro unsprayed plots Hexazinone (sprayed twice) Glyphosate Tuber gerination f% of unsrraved control) Despite the slight reduction in viability (Table 9) it could not be concluded that the treatents had prevented or eliinated any C. rotundus copetition. Crop easureents show that there was no arked difference in crop growth between treatents which is to be expected because no treatent controlled C. rotundus adequately and any control which was obtained, was probably too late to affect cane growth. Aetryne or MSMA caused severe scorching in variety N8 but this effect eventually disappeared. Experient The relationship between C. rotundus infestation (using the ean of plant population counts ade on four occasions) and crop easureents is shown in Figure 5. t was expected that gerination of cane would be affected by copetition fro C. rotundus. The population at an early stage (1,5 onths) provides an indication of the effects on gerination. The results show that there is a distinct decrease in crop growth with increasing infestations of C. rotundus, while a arked increase in crop growth appears to be associated with low populations of the weed. Experient 3 1 NE 15 \ a n i year later n TABLE 8 C. rotundus populations and visual ratings of C. rotundus in Experient 3 1 (oxynil + 2, 4D) 2 MCPA + S (full rate) 3 MCPA + S (high rate) 4 Aetryne + (ioxynil + 2, 4D) 5 Aetryne + MSMA (full rate) 6 Aetrvne + MSMA [half rate) 7 (~oxynil + 2,4D) + 'MSMA ' 8 MSMA 9 MCPA + Daraauat 1 ~exazinonk repeated 11 Hexazinone/diuron + (ioxynil + 2, 4D) 12 Diuron + fioxvnil D) reated Ratings ( control) 11 Nov 13Dec 4Feb Counts plant2 as Vo of unsprayed 4 Feb Hexazinone rehated (low dose) Glyphosate = Untreated 2 = Hand haed 3 = Aetryne + (ioxynil + 2,4D) repeated 4 = Alachlor + 2,4D + paraquat/aetryne + (ioxynil + 2,4D) 5 = MSMA repeated 6 = Glyphosate repeated FGURE 6 C, rotundus populations at spraying (two onths after harvest). and one year later

6 . C. rotundus control Fro Figure 6 it can be seen that C. rotundus populations ore than doubled fro one crop to the next in untreated plots. Populations were saller in all treated plots than in the untreated plots but only repeated MSMA or glyphosate treatents resulted in a decrease with tie in C. rotundus populations. n the treatent involving hand hoeing, populations were held at the sae level. s in the rows were not controlled in the plots treated with glyphosate because the spray swath was restricted to the interrow for fear of daaging the cane. Crop growth 148 Proceedings of The South African Sugar Technologists' Association June 1984 TABLE 1 Crop easureents at 9 onths of age and visual ratings of C. rotundus control (ean of four assessents on 2 Dec, 7 Jan, 2 Jan and 8 Feb) Crop easureents Ratings popn. (1 OOkh) 1 Unsprayed control 2 Hand hoe 3 Aetryne + (ioxynil + 2,4D) repeated 4 Alachlor + 2,4D + paraquatlaetryne + fioxvnil D) 5 MSMA repeated ' 6 Glyphosate ~ ~ ~ ~ ~ ~ ) 1 The differences in crop growth between treatents were probably due ore to natural variability than to effects of the treatents. There were no obvious benefits to crop growth fro controlling C. rotundus. Discussion 2,3 51,O 33,O 29,o 51,O 8,O 2,13 2,16 2,lO 2,14 2,17 2, Copetitive gects Severe reductions in.yields of plant crops of varieties N8 and N13 were caused by copetition fro C. rotundus on weak sandy soils under rainfed conditions. Crop growth easureents suggest that the weed ay have less effect on NCo 376 grown under igation. Thus a variable response to C. rotundus copetition in plant cane can be expected. n ratoon cane, there was no obvious effect of copetition fro C. rotundus. However the difficulty of eliinating C. rotundus fro the 'no C. rotundus' plots before any adverse effects could occur, eant that true coparisons could not be ade in these experients. f there were any benefits fio controlling C. rotundus they ay have been offset by daage to the sugarcane by the herbicide treatents. However easureents suggest that crop growth was not arkedly affected by the herbicide treatents, so the copetitive effects of C. rotundus ay have been very liited in the two experients on ratoon cane. These experients will be onitored during the next ratoon crop where the residual effects fro soe treatents have alost eliinated C. rotundus copetition. Weed control Application of glyphosate to eerged plants was the ost successful ethod of C. rotundus control. A single or repeated application after conventional ploughout was very successful while two applications in iniu tillage plots were even better. t is very difficult to eradicate C. rotundus with glyphosate (Doll et all) and repeated applications are extreely expensive. t is usehl for controlling weeds in the interrow of ratoon cane but is ineffective for weeds in the rows where control is probably ore iportant. Weed control and iproveent in crop growth in plant cane was liited when EPTC was used shortly before planting. n ratoons, treatent with glyphosate and repeated applications of MSMA were able to reduce the weed population fro one crop to the next and this ay have a beneficial effect on the growth of the following ratoon crop. Single applications of MSMA were not effective. The long ter residual action of a herbicide such as hexazinone applied to the soil appeared to reduce plant populations when the treatent was repeated but again there was no advantage to the growth of that particular ratoon. Any benefits in the following ratoon will be recorded. Conclusions cane ay suffer severely fro the effects of copetition fro C. rotundus but this ay vary depending on conditions, eg oisture stress is likely to increase the effect. The ost suitable ethod for reestablishing cane fields infested with C. rotundus appears to be the use of glyphosate on newly eerged C. rotundus plants after conventional ploughout. Further work is necessary to investigate rates and ethods of application for the best results. The effects of C. rotundus on ratoon cane are difficult to elucidate and herbicide applications to control the weed in ratoon cane should be ade with care and with the knowledge that resulting daage to the crop ay offset the advantage due to treatent. REFERENCES 1. Doll, J. D. & Piedrahita, W. (1982). Effect of glyphosate on the sprouting of Cyperus rotundus L. tubers. Weed Res Vol22: Gosnell, J. M. & Thopson, G. D. (1967). The effects of herbicides on Cyperus spp. Proc S Afr Sug Technol Ass 41: Hol, L. G., Plucknett, D. L., Pancho, J.!., Herbefger, J. P. (1977). The world's worst,wee&. The University Press of Hawau, Honolulu. 4. Meissner, Ruth, Nel, P.C., Sith, N. S. H. (198). The influence of red nutgrass (Cyperus rotundus) on growth and developent of soe crop plants. Proc 3rd Weeds Conf of S Africa: MSR Ann Rep 198, l98i. 6. Thopson, G. D. & Gosnell, J. M. (1963). The results of herbicide trials conducted in the cane belt of Natal 1962/63. Proc S Afr Sug Technol Ass 38: Turner, P. E. T. (). Epta Super and Sutan Plus for control of Cyperus rotundus L. in plant crops of sugarcane. Proc S Afr Sug Technol Ass 57: