+ atrazine and MET 1486 were all active. All the herbicides and

Transcription

1 Agronomy THE RESULTS OF RECENT PRE-EMERGENCE HERBICIDE SCREENING TRIALS FOR SUGARCANE IN SOUTH AFRICA P.E.T. Turner I South African Sugar Association Experiment Station Mount Edgecombe, South Africa ABSTRACT Of 23 new herbicides or herbicide mixtures evaluated, U atrazine, Velpar (DPX 3674), DPX 2851, Velpar + diuron, Destun (MBR 8251), Destun + atrazine, CGA atrazine, CGA CGA 29696, Dowco 291, CGA atrazine, CGA atrazine, BFN + atrazine, MET 1486, EL 103 and AC were active against grasses at certain rates. Velpar, Velpar + diuron, CGA atrazine and MET 1486 gave long term control, whilst SN 40624, LS and Dowco 233 were ineffective at the rates tested. On Cyperus escu/enfus, Velpar, DPX 2851, Destun, CGA atrazine, CGA CGA 29696, Destun + atrazine, Velpar + diuron, CGA $ atrazine, CGA atrazine, CGA atrazine and MET 1486 were all active. All the herbicides and herbicide mixtures with the exception of U atrazine, SN 40624, LS , AC and WL were active on broadleaf weeds. Only EL 103 and Destun showed any activity on Cyperus ro fundus. INTRODUCTION Twenty three new herbicides or herbicide mixtures were evaluated for their effect on Cyperus esculentus, Cyperus rotundus, grasses and broadleaf weed, in five pre-emergence weed control trials during the period The combined results represent the completion of a project initiated in 1973'. Combinations with atrazine (a standard broadleaf weedkiller in the South African Sugar Industry) were used in instai~ces where previous work or data on the product submitted by commercial companies suggested weak activity on broadleaf weeds when used alone. Experiments were conducted in fallow sugarcane fields, some of which contained a few volunteer sugarcane plants. The soil was prepared to an even tilth, as would be required for planting sugarcane, before application of herbicide treatments, which were made by means of a gas operated sprayer or a lever operated knapsack sprayer. Spraying Systems TK5 and TK2,5 floodjets, and 8003,fanjets were used, delivering volumes of from 200 to 350 litres qf wateraper hectare. Treatments were applied to the soil as soon after land preparation as possible, to avoid any weed emergence at the time of spraying. The soil textule, moisture status and climatic conditions were recorded at the establishment ($raying) of each trial. 1405,.! t\ +p

2 1406 AGRONOMY Each sprayed plot was 8 m x 2,5 m in area, with an unsprayed control strip at least 1 m wide around it. Weed control ratings were based on the European Weed Research Council scale of 1-9, where 1 = complete control, 4 = just acceptable control, 5 = just unacceptable control and 9 = no effect. Ratings were done separately for Cyperus e'sculentus, Cyperus rotundus, grasses and broadleai weeds, each plot being rated in comparison with the surrounding control strip. Standard treatments, herbicides or herbicide mixtures which are currently registered for use in sugarcane fields and which are known to give acceptable weed control, were included for comparison. All standard treatments are underlined in the tables. Descriptions of ~limate and soils at the time of establishment of each trial are given in Table I. TABLE I. Climate and soil data on five experiment sites. Temperature Trial (OC at Soil analysis Soil ~aihfall am). moisture mm Volume weather 0-14 days applied number Dry Yet Clay Silt Sand $ 0-20 after bulb bulb $ $ $ cm spraying 1 25,7 23, ,7 320 Olear I1 23,O 22, , Clear I11 25,O 23,O ,O Clear IV >10, Overcast V 14,5 14,O h10,o Drizzling EXPERIMENTAL PROCEDURE AND RESULTS ; 1 Experiment I. The herbicides were applied to a Cartref series soil which was dry at the time of spraying, but 52,7 mm of rain were recorded within 14 days after treatment. Dominant weeds which germinated in the control areas were: Cyperus esculentus, Eleusine indica and Commelina benghalensis. Standard treatments included for comparison were alachlor + atrazine, Sencor, 2,4-D amine, MCPA and diuron. Mean visual ratings of weed control made 36, 56 and 77 days after spray application are presented in Table 11. Treatments are listed in order of decreasing effect on grasses, these being the most important weed group in South African sugarcane fields. Rates of herbicides are given in kilograms (kg) or litres (1) of active ingredient (ai) or acid equivalent (ae j per hectare. \I, 1 i 5 ',

3 P.E.T. TURNER 1407 TABLE 11. Mean visual weed control ratings made 36, 56 and 77 days after treatment in Experiment I. - - Experiment ZZ. Five herbicides selected from Experiment I were applied to a Shortlands series soii which received 79 mm of rain during a 14 day period after spraying. Dominant weeds in the control areas were: Panicum glabrescens, Echinocloa colonum, Rottboellia exaltata, Conzmelina benghalensis, Hibiscus trionum and Acalypha ecklonii. Standard treatments included for comparison were: alachlor + atrazine and Sencor. Mean visual ratings of the control of broadleaf weeds and grasses, 50 and 70 days after spray application are presented in Table 111. Treatments are arranged in order of decreasing effect on grasses. F,sL, t )'.>, v/,44,l

4 I 1408 AGRONOMY TABLE 111. Mean visual weed control ratings made 50 and 70 days after treatment I in Experiment 11. Treatments Mean ratings Herbicide litres ai or ae/ha Grasses 1 Broadleaf Velpar Velpar Destun DPX ,8 CGA atraz$~el2,0 + 1,O Destun I 2,25 DPX ,5 4,3 Alachlor + 5,5 6,8 CGA atraeine11,5 + 1,0 12,8 4,O 1 4,O 5,3 Sencor EL 103 n 103 ' r' '5 5 Experiment 111.,I' Two new herbicides, 1 new mixture and 4 previously tested herbicides or herbicide mixtures were compared with 5 standard treatments on a sandy loam soil which received only 5 mm of rain during the 14 days after spraying, although a further 46 mm w(ere recorded during the ensuing two weeks. Dominant weeds which germinated in the control areas were: Cyperus rotundus, Amaranthus spinosus, Nicandra physalodes, Portulaca oleracea, Datura stramonium, Lepidium didymus and Cleome monophylla. The standard treatments included for comparison were: alachlor + atrazine, Sencor, Sencor + diuron, MCPA and 2,4-D amine. Mean visual ratings of weed control 29, 43, 63 and 84 days after spray application are presented in Table IV. Treatments are arranged in order of decreasing effect on broadleaf weeds. Experiment ZV. Promising herbicides and herbicide mixtures were applied to a moist clay ioarn which received 40 mm of rain during the 14 days following treatment. Weeds which dominated the control areas were: Bidens pilosa, Commelina benghalensis and Flaveria bidentis. Standard treatments included for comparison were: Sencor, alachlor + atrazine, Sencor + diuron and MCPA. Mean visual ratings of weed control 33 and 51 days after spray application are presented in Table V. Treatments are arranged in order of decreasing effect on broadleaf weeds.

5 P.E.T. TURNER TABLE IV. Mean visual weed control treatment in Experiment 11, Herbicides Treatments Y I Rate in kg or litres ai or ae/ha ratings made 29, 43, 63 and 84 days aftel -- TABLE V. Mean visual ratings of b~ treatment in Experiment I L Treatments ' Rate in! kg or Herbicides lityes days days ai or ae/ha Sencor ,O 235 Alachlor + atrazine Sencor + diuron ~estun'+ atraeine Destun + atrazine Dowco 291 CGA atraeine MCPA Dowco 233 Destun + cyanazine Velpar Destun + cyanazine = ladleaf weed control 33 and 51 days after Mean ratings

6 1410 AGRONOMY Experiment V. Eleven test herbicides and 3 standard herbicides and herbicide mixtures were applied to a moist Longlands series soil which received 51 mm of rain in the 14 days after spray application. Weeds dominant in the control areas were: Cyperus esculentus, Eleusine indica and Panicum maximum. Standard treatments included for coirlparison were: alachlor + atrazine, metribuzin and 2,4-D amine. Mean visual ratings of weed control 23, 30, 44 and 105 days after application are presented in Table VI. Treatments are arranged in order of decreasing effect on grasses. TABLE VI. Mean visual tatipgs of weed control 23, 30, 44 and 105 days after treatment in Experiment V:'. 7'il <$ - Treatments Mean ratings I Herbicides ai or ae/ha Velpar MET 1486 Velpar + diuron CGA atraeine CGA atrazine CGA atraeine I---- CGA atrazine Alachlor + atraeine MET 1486 Destun + atrazine Velpar Destun + atrazine ~estun Destun BFN atrazine Sencor Dowco 291 Dowco 233 FN atrazine

7 P.E.T. TURNER DISCUSSION Pre-emergence control of Cyperus esculentus Herbicides and herbicide mixtures giving control superior to that of the standard alachlor + atrazine treatment were: Velpar, Destun, DPX 2851, Destun + atrazine, CGA atrazine, CGA CGA 29696, CGA atrazine, MET 1486, CGA atrazine, CGA atrazine and Velpar + diuron.3 Exceptional control was achieved by Velpar, Destun, Destun + atrazine, DPX 2851 and CGA atrazine. BFN atrazine was equal in activity to alachlor + atrazine. U atrazine, EL 103, Dowco 291, Dowco 233, AC 92553, LS , SN and the standards MCPA and 2,4-D amine were relatively ineffective. Pre-emergence control oj Cyperus rotundus The only products to show any pre-emergence activity on Cyperus rotundus were EL 103 at 3,O kg ai/ha, and Destun at 3,O kg ai/ha, the latter treatment achieving acceptable control after 43 days. Pre-emergence control of grass Herbicides and herbicide mixtures giving pre-emergence grass control superior to alachlor + atrazine were: Velpar, CGA CGA 29696, DPX 2851, CGA atrazine, Destun, U atrazine, MET 1486, CGA atrazine, Velpar + diuron, CGA atrazine and CGA atrazine. Long term control was achieved by Velpar (0,675 kg a i/ha), MET 1486 (3,5 kg ai/ha), Vepar + diuron (0,45 + f 2,O kg ai/ha) and CGA atrazine (1,6 + 1,6 kg ai/ha) in one experiment. Herbicide less active than alachlor + atrazine, but equai to or better than Sencor, include: BFN atrazine, Dowco 291 and low rates of active herbicides - Destun, Velpar, Destun + atrazine, CGA atrazine. Herbicides less active than both standards - but still providing acceptable control for a period were: EL 103, AC 92553, LS , Dowco 233 and lower rates of the mixtures Velpar + diuron and BFN atrazine, these all being,equal to MCPA or 2,4-D amine. SN did not provide acceptable control at any stage., i 5,

8 1412 AGRONOMY Pre-emergence control oj broadleaf weeds All herbicides and herbicide mixtures except WL 63611, SN 40624, AC 92553, Destun + cyanazine, Dowco 233, Dowco 291, and Destun and Velpar at certain rates, demonstrated adequate broadleaf weed control, being equal or superior to the standard alachlor + atrazine treatment. Long term control was given by.velpar (0,675 kg ai/ha) Velpar + diuron (0,45 + 2,O kg ai/ha) CGA atrazine (1,6 + 1,6 kg ai/ha) and. MET 1486 (3,5 kg ai/ha). In experiment I11 al\ treatments which included atrazine prevented any germination of weed seeds, while treatments which showed control from 29 days obviously did not prevent germination but were effective through uptake by young roots of developing plants. As only 5 nlm of rain were recorded in the 14 days:,after spraying, the other chemicals may not have been sufficiently washed into the soil to reach the zone of weed seed germination. After further rain, however, they may have been absorbed and may thus only then have begun to act. Alternatively all the herbicides may have been present in the soil at the correct depths, but absorption of Sencor, diuron, Velpar and Destun may be far greater by developing roots than by. germinating seeds. Phytotoxicity to sugarcane The only treatments to show phytotoxic symptoms on the sugarcane volunteers, which germinated in two of the experimental sites, were Velpar and DPX 2851 at rates of 2,5 and 4,8 kg aijha respectively. Velpar produced chlorotic leaves while DPX 2851 caused chlorosis and slight stunting of sugarcane. General Of the promising herbicides or mixtures for weed control in sugarcane the products CGA CGA 29696, DPX 2851, CGA atrazine, U atrazine, CGA atrazine, CGA atrazine have been dropped from further evaluation by the various companies. The activity of those remaining is briefly discussed below. Velpar In both heavy (44% clay) and light (5% clay) soils, Velpar alone, at rates of 0,675 kg ai/ha and higher, has shown activity against broadleaf weeds, grasses and Cyperus esculentus far superior to that of alachlor + atrazine and Sencor. At rates of 0,5 kg aijha the activity against broadleaf weeds and grasses, demonstrated by the product alone, has been equal to that of standard alachlor +,atrazine in light soils (6% clay) but inferior in heavy soils (41% clay). At all rates Velpar has been superior to the standard for Cyperus esculeiztus control. At high rates Velpar has shown phytotoxicity to sugarcane but the 0,5 kg ai/ha rate has had no detrimental effect.

9 P.E.T. TURNER Velpar + diuron Velpar + diuron at 0,45 + 2,O kg ai/ha is more active than either of the standard treatments against grasses, of which it gives excellent longterm control, and Cyperus esculentus. At rates of 0,225 $- 0,8 kg ai/ha it was less effective than the standards. 3. Destun At a high rate of 4,5 kg ai/ha Destun was more effective than alachlor + atrazine for Cyperus esculentus, broadleaf and grass control, in both light and heavy soils. At lower rates of 2,25 and 2,O kg ai/ha, activity on broadleaf weeds has been inferior to that of alachlor + atrazine, while the activity on grasses at 3,O and 2,O kg ai/ha has been slightly inferior to that of alachlor + atrazine. Activity at all rates on Cyperus esculentus has been far superior to that of alachlor + atrazine. Destun has shown some activity at high rates against Cyperus rotundus. 4. Destun + atrazine At the rate 2,5 + 1,O kg ai/ha Destun + atrazine is far superior to the standard alachlor + atrazine for Cyperus esculentus control, equal for broadleaf control and slightly inferior for grass control. 5. Destun + cyanazine I At rates of 1,6 + 1,6 and 2,12 + 1,08 kg ai/ha this mixture was less effective than alachlor + atrazine and the atrazine combinations of Destun. 6. CGA atrazine (Primextra) I At the rate of 2,O + 1,O kg ai/ha Primextra showed acceptable control of broadleaf weeds but it was inferior when compared with the standard alachlor + atrazine in a medium soil (19% clay). At a higher rate (3,O + 1,5) broadleaf weed control was equal to that obtained with alachlor +atrazine. On a iight soil (6% clay) Primextra has shown activity equal to that of alachlor + atrazine for grass control and slightly better for Cyperus esculentus control. At rates of 0,8, 1,2 and 1,6 kg ai/ha EL 103 was inferior to the standard alachlor + atrazine treatment in both light (5% clay) and heavy /

10 I AGRONOMY (44% clay) soils for control of grass and Cyperus esculentus while at 1,6 kg ai/ha it was equal to alachlor + atrazine for broadleaf control. At 3,O kg ai/ha excellent long term control of broadleaf weeds was achieved and some activity was shown against Cyperus rotundus, although at no stage did control reach an acceptable level. Its activity on broadleaf weeds was delayed, acceptable control being achieved only after the first 29 days. This delayed action was common to other herbicides such as Sencor and Velpar, possibly indicating that the action of these herbicides occurs after uptake by seedling roots, rather than through inhibition of seed germination. 8. MET 1486 At a rate of 3,5 i/ha the ac6vity of MET 1486 against Cyperus esculentus was acceptable after 30 days, by contrast with that of alachlor + atrazine which was acceptable only up to 30 days. At the same rate, and at 1,75 kg ai/ha, the product controlled grass more effectively than did alachlor + atrazine, the higher rate achieving exceptionally long-term control with no delay in the attainment of acceptable control. CONCLUSION Weed control superior or equal to that obtained with standard treatments has been demonstrated for a number of products. Three of these have recently been registered for use in the South African Sugar Industry. They are : I 1. Velpar + diuron, which is registered as a formulated mixture Velpar K5, for use as a directed spray 011 ratoon cane only. The rate of application is 4,2 kg product/ha, which contains 0,45 + 2,O kg active ingredients of Velpar + diuron. 2. CGA atrazine, which is registered as a formulated mixture Primextra. The rate of application is 6 litres product/ha, which contains 2,O + 1,O litres or kg active ingredients/ha. 3. Destun, which is registered alone or in combination with atrazine. The rate of application is 5 kg product/ha or 5 kg + 1,25 kg product/ha. This contains 2,5 + 1,O kg active ingredient/ha. Several of the products evaluated have been withdrawn from further immediate evaluation. These include: CGA 17020, CGA 24704, CGA 29696, U27267, DPX 2851, WL 63611, BFN 7310, AC 92553, LS , 2,4-D lithium, Dowco 291. Of the remaining products,el 103 and MET 1486 warrant further investigation.

11 P.E.T. TURNER ACKNOWLEDGEMENTS I acknowledge my irldebtedness to Mr. G. Iggo who conducted all the experimental work and produced the results. Thanks are also due to the chemical comp 'nies for the supply of product samples and to Huletts Sugar Ltd. fok\&p ovision of trial sites. 1 REFERENCES 1. Iggo, G.A. (1975). Results of screening pre-emergence herbicides for sugarcane. Proc. S. Afr. Sug. Technol. Ass. 49, Approved common name APPENDIX I. HERBICIDES USED Metribuzin Perf luidone Tebuthiuron Fernimine 7 Fernimine 4 Gesaprim 80 Karmex Sencor DPX 2851 CGA CGA CGA CGA MET 1486 U ,4-D Lithate Dowco' 291 Dowco 233 BF'N 7310 WL SN AC ae = acid equivalent wp = wettable powder +p = water soluble powder 1 = liquid

12 141 6 AGRONOMY RESULTADOS Dl3 LAS PRUEBAS DE YERBICIDAS PREEMERGENTES EN LA CARA DE AZUCAR SEMBRADA EN AFRICA DEL SUR P.E.T. Turner RESUMEN De unos 23 yerbicidas nuevos y sus combinaciones de 10s mismos, U f Atrazine, Velpar (DP X 3674), DP X 2851, Velpar + Diuron, Destun (MBR 8251), Destun + Atrazine, CGA Atrazine, CGA CGA 26696, Dowco 291, CGA Atrazine, CGA $- Atrazine, BFN Atrazine, MET 1486, EL 103 y AC demonstrar6n?*kibn contra 10s yerbajos a ciertas concentraciones. El Velpar, el Velpar + Diuron, CGA Atrazine y el MET 1486 resultaron efectivas a un largo plazo, rnientras que SN 40624, LS y el Dowco 233 fueron inefectivos en las dosis usadas'i" 'El Velpar, DPX 2851, Destun, CGA Atrazine, CGA CGA 29696, Destun + Atrazine, Velpar + Diuron, CGA Atrazine, CGA Atrazine, CGA Atrazine y MET 1486, todos fueron efectivos contra Cyperus escu/entus. Todos 10s yerbajos y sus mezclas, con la excepcion de U Atrazine, SN 40624, LS , AC y WL fueron efectivos contra Ibs yerbajos de hoja ancha. Solamente el EL 103 y el Destun demostraron actividad contra Cyperus rotundus.