Plant Protection
 
Tea Weed Management
Weed control in tea

Introduction

Weeds can cause problems in tea growing areas especially when the tea is still young. By 1965, the work on evaluating systems of weed control involving the use of chemical weed killers had reached a stage where advanced practical field control measures were spelt out (14859; Digitarious, 1965]).

As early as 1952, twenty six species covering sixteen families were identified and collected in a herbarium[ii]. Interest in the herbarium apparently waned though recently, work has been started to establish a new herbarium for the important tea weeds in Kenya[iii].

Early work on the control of couch grass and lalang

Early research concentrated on the search for economic methods of eradicating couch grass (Digitaria scalarum) or lalang grass (Imperata cylindrica) instead of cultivation operations which were too severe making weaker both young and old tea[iv]. Preliminary observational experiments were done using substances such as:-

(a) TCA (sodium trichloroacetate) which had a good reputation as a weed killer, but which also affects the tea;

(b) Sovacide, a yellow oil which had proved effective against lalang infestation in Malaya.

(c) Concentrated sulphate of ammonia which had been recorded as being effective against certain Digitaria species in the USA.

Only TCA was effective in controlling couch grass[v]. Due to the successful use of TCA, further experimentation was done with it in the subsequent years and it reduced couch, other grasses and soft weeds[vi]. Based on these results the prospects and advantages of using weed killers were subsequently presented and discussed at the Tea Research Institute of East Africa 3rd Conference[vii].

Later herbicide trials with Dowpon (dalapon - 2,2-dichloropropionate) showed better long-term control of couch grass than TCA[viii] as couch grass continued to be the major weed problem[ix]. TCA was also found to be better than Dalapon for generally clearing of land prior to planting[x].

Herbicides

Herbicides vs. manual weeding

Use of herbicides is much superior to manual weeding[xi]. Summaries were then given on weed control in tea[xii] in which the use of herbicides were encouraged in preference to manual weeding. This made it necessary to educate farmers on the correct use and maintenance of spraying equipment[xiii]. Results of all the previous chemical weed control experiments in Kenya were summarised in 1989 (200543; 32705).

Time of application

In Kenya, tea plantations are kept weed free throughout the crop cycle. But a number of crops can coexist with weeds during certain stages of the crop cycle. Experiments were done to determine the critical stage of the tea crop when competition with weeds leads to crop losses which are so large that they justify the costs of weeding[xiv]. Crop performance decreased as weed removal was delayed from the period of planting.

Comparison of herbicides

Formal herbicidal investigations were started in 1962. Karmex, Eptam, Amizine, Fenotiol, Benzac, Simazine, 2-4-Dow, Hyvar and Amiben[xv] were compared in these studies. The results can summarised as follows:

(a) Karmex was shown to be the best pre-emergence weed killer tested.

(b) Simazine was less effective than Karmex as a pre-emergence herbicide and had no effect on young weeds;

(c) All triazine herbicides tested killed weeds effectively.

(d) Paraquat (gramoxone) was a startlingly effective desiccant giving a complete kill when applied to young weeds. Indeed a mixture of Karmex and Paraquat (2 gm, 1 cc) gave excellent control.

(e) Simazine did not control any grass.

For standing broad-leaved weeds, Diuron was outstanding and Linuron and Simazine gave significant effects (13280).

Paraquat and Gramoxone

Methods of keeping tea plantations without weeds were summarised in 1963[xvi]. Paraquat was shown to completely kill Kikuyu grass with repeated applications, Gramoxone only scorched weed leaf even with use of surfactants like Teepol and Agral 90, and Paraquat completely controlled young weeds[xvii] and weeds generally[xviii]. Amitrole was established as a post-emergence herbicide for use in a mixture with persistent herbicides for control of resurgent weeds[xix]. Although guidelines on economising the use of Gramoxone in controlling weeds were also given[xx].

Mixtures of herbicides

Mixtures of herbicides controlled weeds in young or pruned tea[xxi]. The predominant weeds were Kikuyu grass (Pennisetum clandestinum Chiov), and Nutgrass (Cyperus spp). The herbicide mixtures enhanced the performance of individual herbicides. The best results for controlling Kikuyu grass and Nutgrass were obtained with a cocktail of Fusilade/Roundup. Individually Roundup gave the best result. However, Roundup reduced shoot growth rate of tea (202441). Dalapon-Paraquat mixture was effective in controlling Kikuyu grass[xxii]whilst the troublesome weed Oxalis latifolia was found to be controlled by Roundup or Dalapon-Gramoxone mixture (16928; 235731).

Round-up

Trials with Roundup showed that it affected tea bushes, making it important that it does not get into contact with tea bushes[xxiii]. Roundup (Glyphosate) showed a higher percentage of weed control than either Gramoxone or hand weeding[xxiv]. The symptoms of the effect of Roundup began showing on weeds about two weeks after spraying and consisted mainly of severe chlorosis. Roundup had a prolonged effect on the weeds Cyperus rigidifolius Stend, Kyllinga bulbosa P. Beaur and Mariscus keniensis Kuk.

Further experiments were performed in 1983 to assess the performance of different rates of glyphosate (Roundup) in controlling sedges (Cyperus spp) couch grass (Digitaria scalarum L.) and Kikuyu grass (Pennisetum clandestinum).

Gallant and Basta

Further experiments compared the effects of Roundup, Goal, and Gallant EE on Kikuyu grass (Pennisetum clandestinum)[xxv]. Roundup showed considerable weed reduction after two weeks whereas Gallant EE showed reduction after four weeks. Sensor and Goal had minimal effects on Kikuyu grass. More experiments compared Roundup, Gramoxone, Gallant EE, Roundup/Gallant EE mixture and Gramoxone/Gallant EE mixture (06696; 241631). Roundup was significantly superior to Gramoxone and Gallant EE, followed by Gallant EE and finally Gramoxone. Tank mixtures at half rates and Gallant EE/Roundup mixture was equal to Roundup alone at full rate, but Gallant EE/Gramoxone mixture was inferior even to Gallant EE alone.

Basta, a non-selective partially systemic contact herbicide, was compared with Roundup and Gramoxone in the control of perennial grasses (05684; 05576; 21034). Performance of Basta improved with concentration and at 5 L/ha it performed as well as Roundup[xxvi]. Gramoxone only scorched the leaves indicating that the herbicide use on Kikuyu grass and related grasses was not satisfactory. The effectiveness of Basta improved with repeated applications and increased rates (05684; 241633; 21034).

MON series of herbicides

Further trials evaluated the use of MON 1477 on annual tea weeds[xxvii]. High rates of MON 1447, MON 8751 and Basta were necessary for the control of soft weeds.

Pillaround and Pillaroxon were evaluated on the control of perennial grasses[xxviii]. Pillaround was equivalent to Roundup in the reduction of the accumulation of biomass. Focus at 5 L/ha was better than all the contact herbicides, but was inferior to Pillaround and Roundup.

Kamata

The effectiveness of Kamata as a herbicide was compared with Basta and Gramoxone[xxix]. Spraying at 2 week intervals gave the best results against weeds for all the three herbicides. Gramoxone was the best followed by Kamata then Basta. However, yields from Gramoxone treated plots were lower than the control, while Kamata and Basta were slightly better.

Use of wetting agents

Round-up was evaluated with and without Ethokem or Frigate wetting agents[xxx]. Both Ethokem and Frigate enhanced the performance of Roundup in controlling sedges, couch and Kikuyu grass. The two wetting agents could be exploited in reducing the costs of Roundup by applying low rates of the herbicides mixed with the wetting agents. Ethokem appeared slightly better than Frigate.

The effect of herbicides on tea

Some herbicides were shown to have phytotoxic effects on tea[xxxi]. Although many chemicals were tried for phytotoxic effects on weeds, only Diuron and a Triazine synergised with amitrole showed good results (13273). Ground spray of Paraquat did not affect tea[xxxii]. Herbicide mixtures affected tea (13276; 13335) but reduced weed growth[xxxiii].

Use of herbicides did not affect yields in some fields[xxxiv] whilst reducing yields in others[xxxv]. Use of 2,4,5-T killed the tea plants[xxxvi]. Gramoxone spray was thought to contribute to uneven recovery from pruning[xxxvii].

Aboricides to kill trees

Some arboricides were tried in an experiment to kill trees[xxxviii]. Diesel oil had a small effect initially, from which the tree recovered. Use of 2,4,5-T depleted the starch reserves of the trees[xxxix].

Alternative weed control methods

To seek alternative and cheaper methods of weed control in young tea, mulch grass, sawdust and black polythene mulches were compared with conventional herbicides[xl]. Preliminary data indicate mulched and herbicides plots have significantly higher stem girth than the control.




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[i] Digitarus. 1965. Tea without weeds: A TRI Summary Tea, 3(6), 24-34.

[ii] Eden T. 1952. Herbarium. Tea Research Institute of East Africa Annual Report 1952, pp 26.

[iii] Otieno W. 1992. Establishment of a herbarium of important tea weeds. Tea Research Foundation of Kenya Annual Report 1992, pp 144.

[iv] Eden T. 1953. Weed killers. Tea Research of East Africa Annual Report 1953, pp 21-22.

[v] Eden T. 1953. Weed killers. Tea Research of East Africa Annual Report 1953, pp 21-22.

[vi] Goodchild NA. 1954. Weed killers. Tea Research Institute of East Africa Annual Report 1954, pp 27-28.

[vii] Child R. 1955. Chemical weed killers. Tea Research Institute of East Africa Pamphlet No. 12, pp 29-37.

[viii] , ;, ; Goodchild NA, Foster-Barham CB. 1956. Weed killers. Tea Research Institute of East Africa Annual Report 1956, pp 29-30; Howarth NL. 1960. Dalapon spraying for couch control. Tea Research Institute of East Africa Pamphlet No. 17, pp 20-22.

[ix] Fleming SD. 1959. Couch the old enemy of clean plantation crop. Tea, 1(1), 34-40.

[x] Willson KC. 1967. Herbage killers for land clearance. Tea Research Institute of East Africa Annual Report 1966/67, pp 27.

[xi] 14859; Sudoi V, Otieno W. 1994. Weed control in tea. Tea Research Foundation of Kenya Annual Report 1994. pp 149.

[xii] Newing GG. 1971. Weed control in mature tea. Tea, 12(2). 24-25; Tolhurst JAH. 1970. Herbicides for tea. Tea, 17(2), 11-13; Willson KC. 1972. Paraquat, mulch and the mineral nutrition of tea. Outlook on Agriculture, Tea, 7, 74-78; Outran DJ. 1970. The practical application of Paraquat in tea and coffee. Proceedings of the 4th East African Herbicide Conference, 1970 pp 174-180; Willson KC. 1963. Herbicidal investigations. Tea Research Institute of East Africa Annual Report 1963, pp 42-43.

[xiii] Karani WJ. 1974. Care and maintenance of sided spraying equipment. Tea in East Africa 14(2), 25-27.

[xiv] Onsando JM. 1991. Determination of critical period of weed competition on tea and long term effects on the establishment, yields and quality. Tea Research Foundation of Kenya Annual Report 1991, pp 215-216; Otieno W. 1992. Determination of critical period of weed competition with tea and its long term effects on establishment and quality. Tea Research Foundation of Kenya Annual Report 1992, pp 144-145; Sudoi V, Otieno W. 1993. Determination of critical period of weed competition with tea and its long term effects on establishment and yields. Tea Research Foundation of Kenya Annual Report 1993, pp 188.

[xv] Green MJ. 1962. Herbicidal investigations. Preliminary studies. Tea Research Institute of East Africa Annual Report 1962, pp 30-34.

[xvi] Anon. 1965. Tea Estate Practice 1965; Willson, K.C. (1963) The future of chemical weed control Tea, 4(3), 29-33.

[xvii] Willson KC. 1964. Paraquat trials Timbilil Estate. Tea Research Institute of East Africa Annual Report 1964, pp 31-39.

[xviii] 13327; Outran DJ. 1970. The practical application of Paraquat in tea and coffee. Proceedings of the 4th East African Herbicide Conference, 1970 pp 174-180.

[xix] Willson KC. 1964. Herbicidal investigations. Tea Research Institute of East Africa Annual Report 1964, pp 34.

[xx] Chennery EM, Willson KC. 1964. Economising on the use of Gramoxone. Tea, 5(2), 23.

[xxi] 582; 300055; 12274; Magambo MJS, Kilavuka CI, Omollo JG. 1983. The performance of some herbicides tank mixtures in controlling perennial grass weeds in tea. Tea, 4(1), 31-37; Magambo MJS, Kilavuka CI. 1983. Performance of some herbicides tank mixtures in controlling perennial grasses in tea fields. Tea Research Foundation of Kenya Annual Report 1983, pp 101-104.

[xxii] 16371; Kilavuka CI, Magambo MJS 1977. The effect on Kikuyu grass of a Dalapon-Paraquat mixture. Tea in East Africa, 12(1), 13-15.

[xxiii] Magambo MJS, Kilavuka CI. 1975. Effect of Roundup on tea bushes. Tea in East Africa 15(2), 17-18; Magambo MJS, Kilavuka CI. 1975. Effect of Roundup on tea bushes. Tea Research Institute of East Africa Report 1975, pp 80; Magambo MJS, Kilavuka CI. 1975. Preliminary observation on the effect of Glyphosate on Cyperus weeds in young tea. Tea in East Africa 15(1), 11-14.

[xxiv] 240186; Magambo MJS, Kilavuka CI. 1975. Effect of Glyphosate (Roundup) on Cyperus weeds in young tea. Tea Research Institute of East Africa Annual Report 1975, pp 79-80; Magambo MJS, Kilavuka CI. 1975. Preliminary observation on the effect of Glyphosate on Cyperus weeds in young tea. Tea in East Africa 15(2), 17-18.

[xxv] 201976; Magambo MJS, Kilavuka CI, Omollo JG. 1986. Comparison of effects of Roundup, Sensor, Goal and Gallant EC on Kikuyu grass (Pennisetum clandestinum). Tea Research Foundation of Kenya Annual Report 1986, pp 62-63.

[xxvi] Onsando JM. 1988. Basta trial on tea weeds. Tea Research Foundation of Kenya Annual Report 1988, pp 147-149; Onsando JM. 1988. Basta trial on tea weeds: Frequency of application. Tea Research Foundation of Kenya Annual Report 1988, pp 149-150.

[xxvii] 31147; Onsando JM. 1989. Evaluation of MON 1447 on control of Annual Weeds. Tea Research Foundation of Kenya Annual Report 1989, pp 145-147.

[xxviii] Onsando JM. 1990. Evaluation of Pillaround and Pillroxone on control of perennial grasses. The Research Foundation of Kenya Annual Report 1990, pp 171-172.

[xxix] Sudoi V, Otieno W. 1993. Frequency of application of Kamata (MON 8751), Basta, and Gramoxone to control weeds in young tea: Effects on weed growth and yield of tea. Tea Research Foundation of Kenya Annual Report 1993, pp 190-192.

[xxx] 20870; Magambo MJS, Kilavuka CI, Omollo JG. 1985. Comparison of the influence of Ethokem and Frigate on the performance of Glyphosate (Roundup) in controlling some perennial grass weeds. Tea, 6(1), 14-19.

[xxxi] Willson KC. 1962. Phytotoxicity of herbicides. Tea Research Institute of East Africa Annual Report 1962, pp 34-36.

[xxxii] Willson KC. 1963. Phytotoxicity to tea bushes of paraquat ground sprays. Tea Research Institute of East Africa Annual Report 1963, pp 44; Willson KC. 1964. Phytoxicity to tea bushes of Paraquat ground sprays. Tea Research Institute of East Africa Annual Report 1964, pp 34.

[xxxiii] 3278; 13284; 13334; Willson KC. 1964. Herbicide experiment, Chebown Estate. Tea Research Institute of East Annual Report 1964, pp 35.

[xxxiv] 15404; Templer JC. 1969. Herbicides. Tea Research Institute of East Africa Annual Report 1968/69, pp 47-50.

[xxxv] Willson KC. 1967. Herbicide application. Tea Research Institute of East Africa Annual Report 1966/67, pp 26-27.

[xxxvi] Templer JC. 1977. Killing tea with 2,4,5-T. Tea in East Africa, 17(1), 4.

[xxxvii] 235727; 639; 16927; Kilavuka CI, Magambo MJS 1979. Does Gramoxone contribute to uneven recovery from pruning. Tea in East Africa 19(1), 9-10; Kilavuka CI, Magambo MJS. 1979. Herbicide trial. Tea in East Africa, 19(2), 8-10.

[xxxviii] Willson KC. 1963. Arboricide experiment, Chomogonday Estate. Tea Research Institute of East Africa Annual Report 1963, pp 51; Willson KC. 1964. Arboricide experiment. Tea Research Institute of East Africa Annual Report 1964, pp 39-40; Willson KC. 1965. Arboricides on trees. Tea Research Institute of East Africa Annual Report 1965, pp 29.

[xxxix] Kilavuka CI. 1976. An observation of the effect of 2,4,5-T on starch reserve in roots. Tea in East Africa, 16(2), 20-21.

[xl] Onsando JM. 1991. Efficacy of conventional herbicides compared to mulch grass, sawdust, and black polythene in young tea. Tea Research Foundation of Kenya Annual Report 1991, pp 216; Otieno W. 1992. Efficacy of conventional herbicides and hand weeding compared to that of grass, sawdust and polythene mulches in young tea. Tea Research Foundation of Kenya Annual Report 1992, pp 145-146; Sudoi V, Otieno W. 1993. Efficacy of conventional herbicides and hand weeding compared to that of grass, sawdust and polythene mulches in young. Tea Research Foundation of Kenya Annual Report 1993, pp 189-190.

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