Coconut Research Institute Repository

Bandaranayake, C.K.

Happy mapping as an alternative to overcome the problems in coconut genome mapping

Sarathchandra, S.R.

Rajapakse, R.H.S.

Wickramananda, I.R.

Life cycle of coconut mite (Aceria guerreronis) and its management using two chemicals

Perera, L.

Fernando, W.M.U.

Decision making in replanting of coconut

Fernando, M.T.N.

Developments of a multiperiod linear programming framework for modeling of coconut- based intercropping systems in Sri Lanka: An empirical illustration

Jayalath, K.V.N.N.

Dissanayake, A.M.U.

Trends in lands extent under coconuts within two decades (1982-2002): Evidence from six districts in Sri Lanka

Wijebandara, D.M.D.J.

Ranasinghe, C.S.

Response of rapid decline affected coconut (Cocos nucifera L.) palms to micro-nutrients and common salt

Samarajeewa, A.D.

Senaratna, R.P.B.S.H.S.

Perera, K.C.P.

COCOS (2004), 16, 37 - 42 
Printed in Sri Lanka 
EFFECT OF DIFFERENT CONTROL METHODS OF IMPER ATA 
CYLINDRICA ON COCONUT (COCOS NUCIFERA) YIELD IN LOW 
COUNTRY DRY ZONE OF SRI LANKA 
A D Samarajeewa, R P B S H S Senaratna and K C P Perera 
Coconut Research Institute, Lunuwila, Sri Lanka 
ABSTRACT 
Five methods of control of Imperata cylindrica (L.) Beauv namely a) 
harrowing with disc harrow, b) Glyphosate (N- Phosphonomethyl Glycine) 
2.88 kg a.i / ha, c) Glyphosate 1.44 kg a.i/ha, d) circle weeding with 
Glyphosate (1.44 kg a.i/ha) along with mechanical slashing rest of the area, 
and e) mechanical slashing were evaluated to determine the cost effective 
method of control of Imperata cylindhca, and to ascertain the effect of 
coconut -Imperata competition on yield of coconut in Low Country Dry zone 
in Sri Lanka. An unweeded plot was used as the control. Experiment was 
arranged in a Randomized Complete Block design with three replicates. 
Treatments were applied twice a year in six months interval. Glyphosate at 
the rate of 2.88 and Glyphosate 1.44 kg a.i/ha gave a significant reduction 
(P<0.05) of weed biomass when compared to other treatments. A significant 
increase (P< 0.05) of coconut yield was observed due to control of Imperata 
in plots with these treatments at two years after imposition of treatments 
.When cumulative average yield of coconut was considered for three 
consecutive years, control of Imperata with Glyphosate gave a 54% 
increase (P<0.01) of nut yield when compared to the unweeded control. 
Cost - benefit analysis of different control methods revealed that the 
application of Glyphosate at the rate of 1.44 kg a.i/ha was the most cost 
effective (undiscounted B/C ratio: 5.9) method of control of Imperata in 
sandy soils in the Low Country Dry Zone of the Coconut Triangle. 
INTRODUCTION 
Coconut is by far the most extensively cultivated plantation crop in Sri 
Lanka. The growth habit of the palm and its' canopy structure requires a 
wide spacing, which permits abundant sunlight available to the understory. 
As a result the unutilized space under coconut could get invaded with 
weeds, which compete for soil moisture and nutrients reducing the growth 
and yield of coconut palm and obstruct routine agronomic practices 
(Liyanage and Liyanage, 1992). Of the perennial grass weeds, Imperata 
cylindrica is the most noxious and troublesome weed not only in coconut 
plantations but also in other crop ecosystems as well (Renaldo et al., 1980). 
37 
This species tolerate shade up to 50% and thrives well under mature 
coconut plantations (Soerjani, 1970). 
Imperata is found abundantly in coconut plantations in Intermediate Dry 
zone of Sri Lanka, particularly in marginal coconut lands with sandy soils. 
The ability of Imperata to thrive well in marginal coconut lands particularly in 
sandy soils, aggravates the problem of weed competition in coconut. This 
emphasizes the importance of eradication of Imperata from coconut lands 
as it is an aggressive, rhizomatus perennial grass, which reproduces 
profusely from both seeds and rhizomes (Mercado, 1986). Of the various 
methods used to control Imperata, impact of repeated slashing and tillage, 
replacement of Imperata with leguminous cover crops and chemical 
methods have been reported by several authors (Mercado, 1986; Liyanage 
and Liyanage, 1992; Renaldo et al., 1980). Although leguminous cover 
cropping has been reported to be the most effective method of controlling 
Imperata (Renaldo et al., 1980), it is difficult to establish leguminous covers 
in coconut lands with sandy soils. This study envisages to find the 
effectiveness of use of several mechanical and chemical means of control 
Imperata and to assess the impact of coconut - Imperata competition on the 
yield of coconut. 
MATERIALS AND METHODS 
The experiment was conducted at Mangalaeliya in Puttlam District in low 
country dry zone of Sri Lanka from 1997 to 2000. Soil at the location was 
sandy and belongs to the great soil group of Sandy Regosols. The mean 
annual rainfall and temperatures were 1492 mm and 23.8-31.5 0 C, 
respectively. Following treatments were imposed. 
T1 - Harrowing with disc harrow 
T2 - Application of Glyphosate 2.88 kg, a.i. / ha 
T3 - Application of Glyphosate 1.44 kg, a.i. / ha 
T4 - Circle weeding with application of Glyphosate (1.44 kg, a.i. / ha) 
and slashing the rest of the area 
T5 - Mechanical slashing of Imperata 
T6 - Unweeded (control) 
The experiment was laid in a randomized complete block design with three 
replicates. Each plot comprised of six effective palms of around thirty years. 
Slashing was done with a tractor-mounted rotary slasher while harrowing 
was done to a depth of 15 cm using tractor mounted disc- harrow. Spraying 
of weedicide was done with a knapsack sprayer. Treatments were imposed 
twice a year in six monthly intervals. Weed biomass was ascertained by 
quadrate sampling (0.5m 2 quadrate) followed by oven drying at 105 °C for 
38 
24 hrs. Harvesting of coconut palms in each plot was done at two monthly 
intervals. Total yield for a year was obtained from all six palms. 
B/C ratio was used to determine the cost effectiveness of different Imperata 
control methods. Benefits were calculated as the average incremental yield 
per year over the Imperata uncontrolled, considering the yields of previous 
three years. 
RESULTS AND DISCUSSION 
Effect of different control methods on reduction of shoot biomass of 
Imperata 
Figure 01 illustrates the reduction of biomass of Imperata due to different 
control methods over time. Of the various methods used, slashing in six 
months interval had the least effect on biomass of Imperata. According to 
Sandnam et al., (1977), slashing at shorter intervals, results in better control 
of this weed. However slashing Imperata at shorter intervals in coconut 
lands may not be cost effective. Disc harrowing in six month- interval has 
reduced the biomass of Imperata better than slashing. This is probably due 
to the fragmentation of under ground parts thus, desiccation of the 
rhizomes. Effectiveness of control of Imperata by successive soil cultivation 
has been reported by several authors (Knows and Cole, 1973; Ivens, 1975, 
Mercado, 1986). Martin, (1975), has recommended successive tillage with 
disc harrowing at 8-10 week intervals for better control of Imperata. 
Control of Imperata with Glyphosate( N- Phosphonomethyl glycine) at the 
rate of 2.88 and 1.4 kg a.i /ha (Counter-a.i., 356 g/l) gave a significant 
reduction (P<0.05) of weed biomass when compared to other methods. 
Effectiveness of glypohsate for control of Imperata has been reported by 
several authors (Rognon et al., 1984; Wrong 1971; Golan 1976; Mercado, 
1986; Liyanage et al., 1992). Although an integrated approach i.e. 
application of glyphosate followed by establishment of leguminous creeping 
covers was found to be effective in controlling Imperata (Liyanage et al., 
1992; Renaldo et al., 1980), practical difficulties of establishment of cover 
crops in sandy soils in Low Country Dry Zone in the coconut triangle pave 
the way for the present study to opt for alternative methods of control. 
39 
sr 1 5 0 0 
E 
™ 1200-
S 
g 900 -
Q. E 
•S 600-
I 300 -
o S 0 
1997 1998 1999 2000 
Years 
- A- - - Harrowing (Twice/year) • Gtyphosate( 8 l/ha) — •—Glyphosatef 4 l/ha) 
—H Circle weeding/Slashing — •» - -Slashing (Twice/year) -knperata uncontrolled 
Figurel: Effect of weed control methods on biomass yield of Imperata 
Effect of Imperata on yield of Coconut 
Control of Imperata resulted in a significant increase (P< 0.05) in nut yield 
over the uncontrolled plots even a year after imposition of treatments. 
Impact of Imperata on nut yield was clearly shown after 2 years of treatment 
application, where increase in nut yield was 102% and 49% respectively 
with glyphosate treatments (average of two concentrations) when compared 
to unweeded control in the years 1999 and 2000. When the cumulative yield 
of 3 years were considered, control of Imperata with glyphosate has 
increased the nut yield by 55 %, when compared to the unweeded control. 
Imperata cylindrica is a strong competitor for soil nutrients and moisture 
resulting in poor growth and reduction of nut yield (Renaldo et al., 1980). 
Martin and Mudlier (1983) reported a reduction of copra yield by 14 % due 
to coconut- weed competition in general. However literature on degree of 
competition exerted by Imperata on yield of coconut is scarce. 
Of the rest of the treatments, control of Imperata with harrowing or slashing 
did not contribute for a significant increase in nut yield on yearly basis 
(Tablel). Eighty percent of the root zone of coconut is confined in the 
circular area with in the radius of 2m from the coconut boll (Liyanage, 1985), 
which is referred to as "manure circle". It is expected to keep the manure 
circle free from weeds to reduce the coconut-weed competition. However 
the present study showed that weeding in the manure circle with glyphosate 
has not significantly reduced the coconut- weed competition (Fig. 2) in the 
case of Imperata infestation. 
40 
Table 1: Effect of different control methods of Imperata on yield of coconut 
Treatments Year 
1997 1998 1999 2000 Cumulative average 
yield per palm1 
Harrowing 31 43 56 56 52(18) 
Glyphosate 2.88 27 45 88 72 69(56) 
kgs, a.i. / ha 
Glyphosate 1.44 32 54 82 65 67(52) 
kgs, a.i. / ha 
Circle weeding 33 35 56 57 51(16) 
with Glyphosate 
Slahing 33 45 60 55 53(20) 
Unweeded 35 45 42 46 44 
control 
Significance NS * ** * ** 
C V % 10 16 13 7 
LSD 9 19 14 8 
NB. Values were rounded to the nearest digit. 
'Cumulative annual average yield for year 1998,1999 and 2000 
* = Significance at 5 %,** = Significance at 1% , NS = Not significant 
Values in parentheses are the percentage increase of nut yield over the control 
Cost/Benefit analysis of control methods of Imperata 
Table 2 : Costs and benefits of different control methods of Imperata 
Method of Costs* Average Incremental Undiscounted 
control (Rs/ha/ annual benefits (Rs.)^ B/C ratio 
annum) incremental @ Rs.9.00/nut 
yield/ha 
Harrowing 6000.00 1280 11520.00 1.92 
Application of 
Glyphosate 2.88 9600.00 4000 36000.00 3.75 
kgs, a.i. / ha • 
Application of 
Glyphosate 1.44 5600.00 3680 33120.00 5.91 
kgs, a.i. / ha 
Circle weeding 
with Glyphosate 9500.00 1120 10080.00 1.06 
and slashing 
Slahing 7500.00 1440 12960.00 1.73 
Values are in Sri Lankan Rupees (I US$= SLR. 102.00) 
* Include material machinery and labour costs for twice a year 
Average price of commercial product of Glyphosate : Rs. 400/liter (360 g a.i./litre) 
Average labour wage: Rs.200/manday 
41 
The costs of different methods of control of Imperata are given in the Table 
2. Although the highest increase of nut yield was achieved in plots treated 
with glyphosate at 2.88 kg of a.i. /ha, the highest returns to investment (B/C 
ratio: 5.9) was given by the plots treated with glyphosate at 1.44kg a.i./ha, 
thus making it the most effective method of control of Imperata among the 
tested treatments. 
CONCLUSION 
Imperata cylindrica is a strong competitor for coconut reducing, the nut yield. 
This study showed that control of Imperata with glyphosate in coconut lands 
with sandy soil in low country dry zone increased the nut yield by 55% when 
compared to that of unweeded plots. Application of glyphosate at the rate of 
1.44 kg a.i (4 litres of commercial mixture; Counter-a.L, 356 g/l) found to be 
cost effective method of controlling Imperata in coconut lands in low country 
dry Zone. 
REFERENCES 
Renaldo G. and San Juan C. (1980). Replacement of 'Cogan" (Imperata 
cylindrica. (I.) Beau, vegetation under coconut with leguminous cover 
crops, The Philippine Journal of COCONUT STUDIES, pp 32- 39 
Liyanage, L.V.K. and Liyanage, M.de.S (1992). Weed control- Understory 
weed management in coconut lands, CORD (1) viii. pp 48-56. 
Soerjani.M. (1970). Alang-alang, Imperata cylindrica (L.) Beauv. Pattern of 
growth as related to its problem of control, BIOTROP Bull.(1) pp88. 
Beatriz L. Mercado (1986). Control of Imreata cylindrica. In. Weed control in 
Tropical Crops ( Ed. K.Moody ), Vol.ll, Philippines Weed Science 
Society, pp 269-278. 
Sandanum, S. and Jayasinghe, H.D. (1977). Manual and Mechanical 
control of Imperata cylindrica on tea lands in Sri Lanka, PANS 23, pp 
421-426. 
Martin, G. (1975). Land preparation of Imperata savannale or grass pasture, 
Oleagineux 30, pp 467-470. 
Martin, M.P.L.D and Mudaliar, T. (1983). Response of coconut to fertilizer 
application and weed control, Fiji Agric.J.45 (2), pp 51-53. 
42 


Effect of different control methods of Imperata Cylindrica on coconut (cocos nucifera)yield in low country dry zone of Sri Lanka

Analysis of coconut populations by microsatellite markers.

Peiris, T.S.G.

Proceedings of the international conference Coconut Research Institute

Chandrasiri,  K.A.S.

Fernando, L.C.P.

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National Science Foundation of Sri Lanka

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