POST-EMERGENCE SPOT CONTROL OF GUINEA GRASS, (PANICUM MAXIMUM JACQ. ) ABSTRACT

Transcription

1 POST-EMERGENCE SPOT CONTROL OF GUNEA GRASS, (PANCUM MAXMUM JACQ. ) G. F. Mason Caroni Research Station, Carapichaima, Trinidad, W.. ABSTRACT Agronomy Nine trials were conducted during 1977 and 1978 to study the efficacy of certain herbicides and herbicidal mixtures as post-emergence spot control treatments for guinea grass (Panicum maximum Jacq.) growing in cane fields. Of the herbicidal spray solutions tried, buthiadzole at 90'0 g/loo liters, glyphosate at 1200 g/loo liters and hexazinone at 360 or 540 g/100 liters effectively controlled the weed. The first two mentioned treatments, however, were moderately to severely phytotoxic to cane, causing stunting and/or death particularly in the case of glyphosate. Hexazinone, which only causpd marginal stunting of the canes adjacent to treated guinea grass clumps, was observed to be the most suitable treatment for spot control. ts use, however, was limited to times when guinea grass growth was vigorous. NTRODUCTON n Trinidad, as in many other countries, guinea grass (Panicum maximum Jacq.) is a major weed in sugar cane fields (Holm et ap). ts unchecked growth for many years near water courses and defunct railway lines has served as reservoir of seed material in this country as has been reported in the case of Queenstand (Javier3) and Mauritius (RochecousteG). Pre-emergence and early post-emergence (seedling) control of this weed is fairly easily achieved with a number of common herbicides. However, late-post emergence control is much more difficult and often manual methods, split herbicide applications and even products severely phytotoxic to sugarcane are the only means of control (Anon1, McAleese4, Pembro ke5, Rochecouste6). Guinea grass is often not noticed until it has attained a moderate size since its early stages of growth or regrowth is morphologically similar to young sugarcane. Further, this weed is shade tolerant and grows unaffected in cane fields, often within cane stools, regardless of the stage of the crop (Holm eta/? Rochecouste6). For these reasons clump cannot be controlled by the normal broad spectrum herbicidal treatments. n Trinidad, therefore, hand-weeding by digging out was the standard method of control and this proved to be slow and costly. For example, to clear a moderately infested four hectare field containing about 15,000 clumps requires in excess of 30 man-days. This paper describes a series of trials which were undertaken in order to obtain a cheaper and more effective means of post-emergence control, 99 r(,. -1

2 ! 1W 1 than manual digging. MATERALS AND METHODS \\line trials were conducted, four in 1977 and five in Each trial was set out in a randomized complete block design with four replications. Plot size in each trial was either 10, 15, or 20 guinea grass clumps. Each clump was individually marked by placing a 0.4 m picket next to or within it, n all cases only the marked clumps were considered for purposes of treatment and subsequent assessments. The herbicidal products used are shown in Table 1. n trials 5 to 9 conducted in 1978 only the two most promising treatments from the trials 1 to 4 of 1977 were retained and applied at two rates each along with two rates of a new product, terbutryn (trade name gran). Control treatments, either unweeded or hand-weeded, were also included in trials 5 to 9. Herbicide applications were done using knapsack sprayers fitted with hollow cone nozzles having a 45' spray angle. n this way the swath width was relatively narrow and so the likelihood of spraying canes adjacent to the weeds was reduced. ndividual clumps were sprayed just to give complete cover but well before the run-off point. Herbicidal treatment rates were taken as the concentration per 100 liters spray solution. TABLE. Description of herbicides used in trials Common Name Trade Name Formulation Manufacturer Trial AmetryneMSMA Gesapax Plus % Ciba-Geigy 4 Buthiadazole Ravage 75% W.P. Velsicol 1 to 9 Cyanatry na Lysof ix 40% S.C. Shell 5 to 9 Glyphosate Roundup 480 glliter Monsanto 1 to 4 Hexazinone Velpar 90% W.S.P. Du Pont 1 to 9 Hexazinonel Diuron Velpar-K 44116% W.P. Du Pont 1 to 2 MSMA Daconate 35% a. i. Diamond 1 to 3 Shamrock Co. Terbutryn lgran 500 glliter Ciba-Geigy 5to9 flowable E.C. awitfidrawn duping Post application assessments were made visually at approximately twoweek intervals and scores recorded as the percent of clumps killed. These *

3 i i assessments were continued for periods ranging from 8 to 13 weeks as conditions permitted. Phytotoxicity to sugarcane was determined by measuring heights of sprayed and unsprayed stalks and calculating the ratio of the former to the latter. RESULTS AND DSCUSSON The results of trials 1 to 4 are summarized in Table 2. From these trials,, buthiadazole was the most effective treatment giving complete control in every trial. Hexat inone was also very effective since complete guinea grass control was achieved in trials 2, 3 and 4. n trial 1, however, hexazinone gave unsatisfactory control. n this trial, herbicide application was made during the dry season when weeds were growing very slowly and leaves were tougher unlike the case in the latter trials when weed growth was vigorous and leaves were soft. Satisfactory control was obtained with glyphosate in trials 2, 3 and 4 and with hexazinone/ diuron in trial 2. However, these two treatments gave little control in trial ', presumably again because of the application being made before the weed resumed vigorous growth. Ametryne/MSMA in trial 4 and MSMA in trial 3 gave moderate control but their action on larger clumps (those taller than 20 cm) was shortlived, regrowth occurring from the base of the clumps after about four weeks. TABLE 2. Per cent guinea grass controlled in cane fields with various herbicides in Trials 1 to 4 Trial No Waterloo Edinburgh Edinbugh Caroni Location Est. 107(154) PF32 (124) Est 38(142) F105 N(383) Cane variety B HJ 5941 B B Date of application 17/5/77 27/5/77 1 1/6/77 22/6/77 No. of clumps/plot Per cent weed control Treatment Date-concn/ 00 liters Days after application AmetryneMSMA g Buthiadazole 900 g Cyanatryna 400/800 g Glyphosate 1200 g Hexazinonea g HexazinoneDiuron g MSMAa g '~owerates were used in Trials and 2.

4 102 AGRONOMY With respect to cane phytotoxicity, buthiadazole and glyphosate were severely phytotoxic, particularly glyphosate which caused neighboring canes to be either killed or extremely stunted. Buthiadazole caused moderate stunting of larger plants and death of small tillers. Hexazinone caused slight to moderate stunting in larger shoots depending upon the quantity of spray to which it was subjected. Table 3 summarizes the extent to which the various treatments affected heights of those primary and secondary stalks which could not be avoided during application. Buthiadazole, glyphosateand hexazinone, in descending order, caused the greatest restrictions in stalk heights. TABLE 3. Phytotoxic effects of herbicides on cane stalks adjacent to treated guinea grass in Trials 1, 2 and Trial Nosa Waterloo Edinburgh Caroni Location Est. 107(154) PH 32 N(124) F 105 (3831 Cane variety B HJ 5741 B Date of application 17/5/77 27/5/77 22/6/77 Stalk height % control Treatment Rate-Concn/l 00 liters Days after application AmetryneMSMA g - 83 Buthiadazole Cyanatryn 400/800 g Glyphosate g Hexazinone g Hexazinone/Diuron g MSMA 875 g 'cane growth in trial 3 was poor due to wader-logging. The results of trials 5 to 9 (conducted in 1978) are summarized in Table 4. Terbutryn was ineffective while buthiadazole and hexazinone were effective at both rates. However, hexazinone at the lower rate gave unsatisfactory control in trials 5 and 6, probably again because of the lack of vigorous growth of the guinea grass at the time of application. The hand-weeded treatments carried out in trials 7, 8 and 9 resulted in varied control from unsatisfactory to good. Despite the care taken to completely remove clumps in all cases, small pieces of the crown which were left behind gave regrowth. Buthiadazole and hexazinone also caused phytotoxicity to the crop in these trials as was observed in the previous year. Table 5 shows the relative

5 TABLE 4. Per cent guinea grass controlled in cane fields with various herbicides in Trials 5 to Waterloo Waterloo Felicite Felicite Caroni Location Est. 11 (348) Est. 12 (349) 3 W 6 (253) 5 W 9 (230) F 105 N 1383) Cane variety B B HJ 5741 HJ 5741 B Date of application 24/4/ /5/78 17/5/78 2/6/78 Nn nf rl~~mns/nlnt "T Per cent weed control *.., _ Treatment Rate-Concn/100 liters Days after application Unweeded Control Control Manual digging Buthiadazole 675 g Buthiadazole 1000 g Hexazinone 270 g Hexazinone 400 g Terbutryn 750 g ' Ter bu tryn 1150g

6 stalk heights due to the various treatments for trials 5, 7 and 8. (Trials 6 and 9 had too little cane to make it worthwhile). n trial 5, where the control was unweeded, heights in all cases exceeded that of the control. n trials 7 and 8 where the controls were hand-weeded, mean sfalk heights were inferior in almost all cases. This, therefore, demonstratesthat stalk heights are curtailed by both the presence of guinea grass and the use of herbicidal spot spraying. TABLE 5. Stalk heights of cane adjacent to herbicide treated guinea grass relative to those in unweeded/manual weeded plots in trials 5, 7 and 8 Trial NO.^ ~aterlbo Felicite Felicite Location Est. 11 (348) 3 W 6 (253) 5 W 9 (230) Cane variety B HJ 5741 HJ 5741 Date of application 24/4/78 17/5/78 17/5/78 Treatment Control Control Buthiadazole Buthiadazole Hexazinone Hexazinone Terbuton Terbutryn Rate-Concn/l00 liters Unweeded Manual digging 675 g 1000 g 270 g 400 g 750 g Stalk heights % control Days after application a~rials 6 and 9 were disrupted before stalk heights measurement by removal of pickets, etc,, by intruders. Post-emergence control of guinea grass can be efficiently achieved by tlie use of buthiadazole at 900 g per 100 liters, glyphosate at 1200 g per 100 liters, and hexazinone at 300 to 450 g per 100 liters. As a spot treatment, however, hexazinone was the most successful because of its relatively lower phytotoxic effect on the cane crop. The phytotoxic effect of this chemical on sugarcane seem to be restricted to stalks which receive direct spray because of their Proximity to the weed. On the other hand, spot spraying with buthiadzaole may cause extreme stunting or death of the cane crop. As a substitute for manual digging, the use of hexazinone would greatly reduce operating costs and these would undoubtedly outureigh any losses due to growth reductions.,hexazinone

7 application CONTROL for successful control of guinea grass, however, seems to be restricted to periods when the weed is growing vigorously. Until further work is successfully carried out, which would make it possible to reduce or eliminate the prospect of crop phytotoxicity, and to extend control to slow growing clumps during the dry season, spot application with hexazinone will prove to be a worthwhile method of control. REFERENCES Anon (1977). Guinea grass in '"Chemical Weed Control" Cane Growers' Quart, Bull. Vol. 40 (31, p. 91. Holm, L:-G., Donald L. Plucknett, Juan V. Pancho and James P. Herberger (1977). Panicum maximum Jacq. in The World's Worst Weeds - distribution and biology. Publ. The University Press of Hawaii, Chapter 54, p Javier, E. (1970). The flowering -. habits and mode of reporduction of guihea grass (Panicurn maximum Jacq.) in Proc. of the 11th ntern. Grassland Congress, edited by M.J.T. Norman, Univ. of Queensland Press, p McAleese, C. M. (1970). Major weeds of the northern district and their control. Cane Growers' Quart. Bull. Vol. 33 (41, p Pembroke, E. A. (1970). The control of weeds in the Mackay area. Cane Growers Quart. Bull. Vol. 33 (3), p Rochecouste, E. (1967). Panicum maximum in weed control in sugar cane. Publ. Mauritius Sugar ndustry Research nstitute, p. 82. DE MERBA DE GUNEA (PANCUM MAXMUM Jacy.) EN POST EMERGENCA CON APLCACONES DRGDAS. G. F. Mason WESUMEN Dmrante 6977 y 1978 se lkvaron a cab0 nueve ensayos para estudiar la eficacia de ciertas herbicidas y mezclas de herbicidas para controlar la hierba de guinea (Panicum maximum Jacq.) creciendo en cafiaverales mediante aplicaciones dirigidas en post-emergencia. De todas las soluciones de herbicidas yrobadas butiadazole a 900 g/100 litros, glifosato a 1200 g/100 litros y hexazinone a 360 o 540 g/100 litros rindieron un control muy bueno de h maleza. Los primeros dos tratamientos mencionados. sin embargo, fueron moderadamente

8 106 AGRONOMY a severamente fitotoxicos para la cafia, impidiendo el crecirbiento y/o muerte particularmente en el caso de glifosato. Hexazinoae que solamente impidio el crecimiento marginal de las caiias adyacentes a amacollos de hierba de guinea tratada se consider0 el trataniiento mas apropiado para aplicaciones dirigidas. Su uso, sin embargo fue limitado a las yeces cuando el crecimiento de la hierbq de gluinea era vigoroso.