Incidence of sugarcane shoot borer under different levels of weed ...

Vol. 4 (3&4) : 149 - 152 (2002)

SHORT COMMUNICATION

Incidence of Sugarcane Shoot Borer under Different Levels of Weed Competition, Crop Geometry, Intercropping and Nutrient Supply Systems J. Srikanth, K.P. Salin, S. Easwaramoorthy and C. Kailasam 1 Section of Entomology, ISection of Agronomy, Sugarcane Breeding Institute, Coimbatore - 641 007, India

The effect of selected agronomic practices on the incidence of sugarcane shoot borer Chilo infuscatellus Snellen (Lepidoptera: Crambidae) w a s examined. In an experiment on critical periods of crop-weed competition, wherein s u g a r c a n e crop was maintained with different weed regimes, the incidence of b o r e r w a s significantly lower in w e e d y crop than in weed-free crop. The study s u g g e s t e d that crop-weed v e g e t a t i o n a l diversity maintained up to 75 DAP may reduce shoot borer populations. In the experiment on crop g e o m e t r y - intercrop c o m b i n a t i o n s with three planting patterns and four intercrops, shoot borer incidence s h o w e d non-significant differences. Similarly, in the trial on nutrient supply systems that included combinations of organic manure, green m a n u r e , sugarcane trash, biofertilizer and chemical fertilizer as sources of nutrients, shoot borer incidence s h o w e d non-significant differences.

KEYWORDS : Sugarcane, crop-weed diversity, crop geometry, intercrops, nutrient systems, shoot borer, Chilo infuscatellus

The long duration of sugarcane confers several advantages on the crop in terms of its amenability to p o l y c u l t u r e s c o m b i n e d with crop g e o m e t r y and m a n i p u l a t i o n of nutrient supply systems. Several cereals, oilseeds, pulses and other crops are grown as intercrops with sugarcane in India (Kailasam, 1994). Planting geometry variations in terms of seed rate and spacing had significant positive effect on yield (Singh et al., 2000). Similarly, biofertilizers have a positive influence on sugarcane yield (Srinivasan and Naidu, 1987).

incidence levels of s u g a r c a n e s h o o t b o r e r Chilo infuscatellus Snellen (Lepidoptera: C r a m b i d a e ) in experiments on weed regimes, nutrient supply systems and crop geometry-intercrop combinations. The study was conducted in the experimental plots of the Discipline of Agronomy, Sugarcane Breeding Institute, Coimbatore, Tamil Nadu State, India. The experiments on weed regimes and integrated nutrient supply systems were laid out in a randomized block design with three replications. The treatments in the weed regime experi.memt, intended to study the critical period of crop-weed competition, consisted of weedy and weed-free maintenance of the crop for different periods (Table 1) in a plot size of 7.2m x 6.0m with eight rows of 6.0m length planted in February. Weedfree plots r e c e i v e d manual w e e d i n g operation at fortnightly intervals. In the experiment on nutrient supply systems, treatments comprised combinations of nutrient sources in the form of organic manure, green manure dhaincha (Sesbania aculeata), sugarcane trash, (Azospirillum spp. and microbial fertilizer phosphobacteria) and chemical fertilizer (Table 2) in a plot size of 5.4m x 6.0m with six rows of 6.0m length planted in April. The experiment on crop geometry and intercropping was a 3 x 5 factorial combination laid out in split plot design with crop geometry as the main

A g r o n o m i c m a n i p u l a t i o n s like i n t e r c r o p p i n g influence incidence of sugarcane pests in different ways (reviewed in Srikanth et al., 2000). Similarly, weedy sugarcane habitats modify pest and natural e n e m y c o m p l e x (Ali et al., 1984; Ali and Reagan, 1985; Srikanth et al., 1997). Although crop geometry appeared to have some effect on pest incidence (Verma et al., 1981; Varun et al., 1994), there appears to be no information on the effect of nutrient supply systems on s u g a r c a n e pests, e x c e p t for reduced shoot b o r e r incidence in trash mulched crop (Avasthy and Tiwari, 1986). In this preliminary work, we examined the

C o r r e s p o n d i n g author : J. S r i k a n t h

Contribution No. : 48/2002-03/SBI 149

differences in s h o o t b o r e r i n c i d e n c e a m o n g s t the three planting patterns, a n d four i n t e r c r o p combinations" and s u g a r c a n e s o l e c r o p w e r e n o t s i g n i f i c a n t for the i n d i v i d u a l factors as w e l l as interactions ( T a b l e 3). The range o f borer infestation in this study too was m o d e r a t e (1.77 - 4.30%).

plot and i n t e r c r o p as sub p l o t (Table 3); the plot size was 9.0m x 6.0m with variable number of rows d e p e n d i n g on the crop g e o m e t r y p l a n t e d in March. Counts of deadhearts caused by shoot borer were r e c o r d e d d u r i n g A p r i l - M a y in all the rows o f individual p l o t s a n d e x p r e s s e d as p e r c e n t a g e . The d a t a w e r e s u b j e c t e d to square root t r a n s f o r m a t i o n and analysis o f v a r i a n c e ( A N O V A ) . The data f r o m weed regimes and n u t r i e n t s u p p l y s y s t e m w e r e s u b j e c t e d to o n e - w a y A N O V A and D u n c a n ' s M u l t i p l e R a n g e Test (DMRT) while the d a t a from crop g e o m e t r y - intercrop study were s u b j e c t e d to two factor a n a l y s i s f o l l o w i n g G o m e z and G o m e z (1984).

P e s t a t t a c k in c r o p s m a i n t a i n e d w i t h d i v e r s e v e g e t a t i o n is r e l a t e d to e n h a n c e d n a t u r a l e n e m y p o p u l a t i o n s , b e s i d e s spatial d i l u t i o n o f the p r i m a r y resource and structural or c h e m i c a l i n t e r f e r e n c e with h o s t l o c a t i o n a n d u s e by h e r b i v o r e s ( r e v i e w e d in Showier e t al., 1990). In general, natural e n e m i e s p l a y a more i m p o r t a n t r o l e in p o p u l a t i o n r e g u l a t i o n in cropw e e d d i v e r s i t y s y s t e m s t h a n in a n n u a l c r o p - c r o p d i v e r s i t y s y s t e m s ( B a l i d d a w a , 1985). A l t h o u g h not r e c o r d e d in this study, the diversity and a b u n d a n c e o f natural e n e m i e s like s p i d e r s ( E a s w a r a m o o r t h y et al., 1994), ground b e e t l e s ( E a s w a r a m o o r t h y e t a l . , 1997) and ants ( E a s w a r a m o o r t h y e t a l . , 1998) in s u g a r c a n e c r o p h a b i t a t a n d t h e i r e n h a n c e d a c t i v i t y in w e e d y h a b i t a t s ( A l i e t a l . , 1984; A l i and R e a g a n , 1985; S h o w i e r e t al., 1990; S r i k a n t h e t al., 1997) w o u l d have partly led to the r e d u c t i o n in shoot b o r e r p o p u l a t i o n in the present study, j u s t as they r e d u c e d o t h e r borers ( S h o w i e r e t a l . , 1990). B e s i d e s e n h a n c i a ~ , ~ s p i d e r p o p u l a t i o n s ( S r i k a n t h e t al., 1997), the n o n - s e l e c t i v e w e e d f l o r a m a i n t a i n e d in the p r e s e n t s t u d y w o u l d possibly have i n c r e a s e d the abundance o f p r e d a t o r y ants which are known to show differential f o r a g i n g ability in sugarcane s e l e c t i v e l y m a i n t a i n e d as grass, b r o a d -

S h o o t b o r e r i n c i d e n c e in s u g a r c a n e crop m a i n t a i n e d with different weed regimes showed significant o v e r l a p p i n g d i f f e r e n c e s at 75 D A P (Table 1). Different t r e a t m e n t s s h o w e d m o d e r a t e r a n g e (0.32 - 2.65%) o f i n f e s t a t i o n , with the e x c e p t i o n o f the crop kept w e e d y up to 60 D A P (6.77%). B o r e r i n c i d e n c e at 75 D A P in w e e d free r e g i m e s (1.93 - 5 . 0 8 % ) showed significant but o v e r l a p p i n g differences. A l t h o u g h the differences at 75 D A P b e t w e e n weed free and w e e d y plots were not c l e a r - c u t , there was a g e n e r a l d e c r e a s i n g trend in b o r e r i n c i d e n c e in plots m a i n t a i n e d w e e d y b e y o n d 30 D A P and an o p p o s i t e trend in w e e d free plots. D i f f e r e n t nutrient s u p p l y s y s t e m s , which i n c l u d e d the green m a n u r e d h a i n c h a g r o w n as intercrop, did not i n f l u e n c e s h o o t b o r e r activity (Table 2). The i n c i d e n c e o f shoot b o r e r in different t r e a t m e n t s (2.00 - 4.78%) was m o d e r a t e . In the c r o p g e o m e t r y and i n t e r c r o p c o m b i n a t i o n s t u d y l a i d o u t in s p l i t p l o t d e s i g n , Table - 1 :

T a b l e - 2 : S h o o t b o r e r i n c i d e n c e in s u g a r c a n e crop m a i n t a i n e d w i t h different n u t r i e n t s u p p l y systems

Shoot borer incidence in s u g a r c a n e m a i n t a i n e d with different w e e d r e g i m e s

Integrated n u t r i e n t s u p p l y system

% shoot borer i n c i d e n c e at 75 D A P

2.56 (1.74) # a-e !

100% chemical fertilizer

2.00 (1.58) # a !

Weedy up to 45 DAP

2.65 (1.76) a-e

25% organic + 50% chemical

3.84 (2.02) a

Weedy up to 60 DAP

6.77 (2.59) e

25% organic + 50% chemical + biofertilizer

2.30 (1.66) a

Weedy up to 75 DAP

0.64 (0.99) ab


4.78 (2.02) a

Weedy up to 90 DAP

1.75 (1.50) a-d

Weedy throughout crop period

1).3-2-(0.89)a

+ dhaincha + trash

Weed free up to 30 DAP

1.93 (t.41) abc

25% organic + 75% chemical

2.72 (1.77) a


2.09 (1.57) a-e


2.26 (1.65) a


3.10 (1.87) b-e


3.09 (1.88) a

Weed r e g i m e

% shoot b o r e r incidence at 75 DAP

Weedy up to 30 DAP

+ dhaincha


2.99 (1.81) a

+ dhaincha


3.27 (1.92) c-e


2.67 (1.76) a-e

+ dhaincha + trash

Weed free throughout crop period

5.08 (2.35) de

Control

4.70 (2.21) a

SEm

0.27

SEm

0.33


# Figures in parentheses are (x + 0.5) 0.5 values ! Means followed by the same letter in the c o l u m n are not significantly different (P > 0.05) by DMRT

2.43 (1.63) a

# Figures in parentheses are (x + 0.5) ~ values Means f o l l o w e d by the same letter in the column are not significantly different (P > 0.05) by DMRT

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Table - 3 : Shoot borer incidence (%) at 65 DAP in sugarcane grown in different crop geometry and intercrop combinations Crop geometry of sugarcane

Intercrop No intercrop

Soybean

Blackgram

Sunhemp

Dhaincha

Mean

Normal rows (90 cm)

1.77 (1.50)#

3.12 (1.82)

2.31 (1.59)

4.30 (2.18)

2.63 (1.76)

2.83 (1.77)

Paired rows (60 / 120 cm)

3.42 (1.96)

2.77 (1.80)

2.99 (1.86)

3.21 (1.91)

2.76 (1.80)

3.03 (1.87)

Wide rows (150 cm)

3.39 (1.92)

1.92 (1.54)

3.54 (1.96)

2.29 (1.64)

2.81 (1.77)

2.79 (1.77)

Mean

2.86 (1.80)

2.60 (1.72)

2.95 (1.80)

3.27 (1.91)

2.73 (1.78)

F-test

Crop geometry

NS

Intercrop

NS

Interaction

NS

# Figures in parentheses are (x + 0.5)0.5 values ! NS: P > 0.05 leaf or weed-flee habitats (Ali et al., 1984). Selective manipulation of weed flora and examination of foraging habits of different predatory groups would reveal their relative predatory efficiency and importance. Such studies would also reveal the possible interference among predatory groups, as was observed between ants and c o c c i n e l l i d s ( S r i k a n t h et al., 2001). H i g h e r abundance and diversity of both ground and foliage a s s o c i a t e d p r e d a t o r s and prey in weedy habitats enhanced cane and sugar yields and returns in dollars/ ha by 19% (Ali and Reagan, 1985). In the absence of such information and in view of the general feeding habits of spiders (Easwaramoorthy et al., 1996), the suggestion that these general groups of predators play only a limited role in the reduction of tissue boring insects like shoot borers (Srikanth et al., 2000) appears reasonable. It is also possible that the luxuriant growth of the p r e d o m i n a n t d i c o t weed P a r t h e n i u m h y s t e r o p h o r u s L., which often outgrows sugarcane seedlings, interferes structurally or chemically with host location of shoot borer more than it enhances the impact of increased natural eriemy populations. Despite the suggestion that judicious vegetational diversification can lead to an ecologically stable plant protection system in sugarcane (Ali et al., 1984; Ali and Reagan, 19~85; Showler et al., 1990) and the significantly lower borer population noticed in some weedy plots in the present study, the possibility of maintaining such vegatative diversity may be limited by agronomic considerations.

(Srikanth et al., 2000). These studies o b v i o u s l y indicated that natural enemies play a less significant role in intercropped sugarcane as suggested earlier (Srikanth et al., 2000). The absence of significant differences in shoot borer incidence in different crop geometry and intercrop combinations in the present study suggested that the variable spatial dilution of the primary resource, i.e. sugarcane, brought about by the different spacing patterns and intercrops was not sufficient to disrupt the host location process. However, main and intercrops planted in variable numbers of rows reduced shoot borer (Varun et al., 1994) and top borer (Verma et al., 1981) incidence. Reduced incidence of shoot borer (Rajendran, 1999; Sardana, 2000) and root borer (Sardana, 2001) was observed in intercrop experiments that used normal planting of sugarcane. The generally low levels of shoot borer incidence in the intercrop experiment of the present study need not undermine the results since similar low levels revealed significant differences in the weed regime experiment. In several earlier sugarcane intercrop experiments (reviewed in Srikanth et al., 2000), the variable results obtained were discussed as being i n d e p e n d e n t of general levels of pest incidence but often related to the relative suitability of intercrop (Srikanth et al., 2000). Variation in pest behavior under different geographical and agroclimatic conditions could be another factor behind such variable results. In the integrated nutrient supply system experiment, nutrients supplied as combinations of different forms sustained uniform levels of shoot borer. The differences in the organic matter content a d d e d to the soil, especially in the treatments with the green manure dhaincha crop and sugarcane trash, apparently did not influence shoot borer incidence. The reduction in shoot borer incidence due to trash mulching could be related more to the increase in sheath moisture (Avasthy and Tiwari, 1986) than changes in organic matter content of soil. In recent studies, Sardana (2001) suggested that incorporation of intercrops as a source of organic matter enhanced root borer incidence at harvest, when

Broad-leaf plants in sugarcane habitat are expected to provide more prey per amount of dry biomass (Ali et al., 1984) and consequently greater natural enemy activity. Our earlier studies (Srikanth et al., 2000) showed significant d i f f e r e n c e s in the numbers of p r e d a t o r s , i.e. spiders and coccinellids, a m o n g s t different pulse intercrops but this did not reflect in shoot borer incidence. In another experiment in the same study, shoot borer was significantly higher in s u g a r c a n e i n t e r c r o p p e d with soybean despite the absence of significant difference in predator numbers 151

Easwaramoorthy, S., Srikanth, J., Santhalakshmi, G. and Kurup, N.K. (1996). Life history and prey acceptance of commonly occurring spiders in sugarcane ecosystem. J. Biol. Control, 10 : 39-47.

in fact the standing intercrops reduced borer i n c i d e n c e in the e a r l y stage of s u g a r c a n e . Such d i f f e r e n t i a l a b u n d a n c e of root borer, which occurs throughout the crop period of sugarcane u n l i k e shoot borer, could be more d u e to diversity related causes (Showier et al., 1990) than variation in o r g a n i c matter c o n t e n t in soil. D h a i n c h a grown as a source o f green m a n u r e in the present study can be c o n s i d e r e d an intercrop in some sense b u t it too did not show reduced shoot b o r e r i n c i d e n c e in much the same m a n n e r as in the intercop e x p e r i m e n t s . I n general, the i m p a c t of an a g r o n o m i c practice like i n t e r c r o p p i n g on pest incidence can be e x p e c t e d to last u n t i l the i n t e r c r o p is h a r v e s t e d . However, it would be i n t e r e s t i n g to study the effect o f other a g r o n o m i c practices e x a m i n e d in this study on different pest p o p u l a t i o n s , p a r t i c u l a r l y at intensities higher than those observed in the present study, and natural e n e m y a b u n d a n c e to f u l l y u n d e r s t a n d their i m p o r t a n c e in sugarcane crop protection. The m i n o r differences in dates of p l a n t i n g in different experiments did not have any i m p a c t on shoot borer i n c i d e n c e recorded two m o n t h s after p l a n t i n g , as could be seen from the moderate i n c i d e n c e in all experiments. The role of time planting, if any, could be proved only when the experiments are repeated under different dates of p l a n t i n g .

Easwaramoorthy, S., Srikanth, J. and Kurup, N.K. (1997). Ground beetles in sugarcane ecosystem: new records and seasonal fluctuations. J. Soil Biol. Ecol., 17(1) : 73-75. Easwaramoorthy, S., Kurup, N.K. and Santhalakshmi, G. (1998). New records and population dynamics of minor arthropod predators in sugarcane ecosystem. Insect Environ., 4 : 98-99. Gomez, K.A. and Gomez, A.A. (1984). Statistical Procedures for Agricultural Research, 2nd edn. John Wiley and Sons, New York, 680p.

Kailasam, C. (1994). Evaluation of nitrogen levels and seed rates for short duration sugarcane (Co 8338) intercropped with three soybean cultivars of varying growth habits. Ph.D. thesis, Tamil Nadu Agricultural University, Coimbatore, India. Rajendran, B. (1999). Management of insect pests of sugarcane through cultural practices. Indian Sug., 49(4) : 271-276. Sardana, H.R. (2000). Impact of companion cropping on the incidence of early shoot borer, Chilo infuscatellus of sugarcane. Ann. Pl. Prot. Sci., 8(2) : 239-240.

Sardana, H.R. (2001). Influence of summer inter-cropping on the incidence of root borer, Emmalocera depressella of sugarcane. Indian J. Ent., 63(1) : 49-51. Showier, A.T., Reagan, T.E. and Knaus, R.M. (1990).~ugarcaneweed community interactions with arthropods and pathogens. Insect Sci. Applic., 11(1) : l-1 I.

ACKNOWLEDGEMENTS The o b s e r v a t i o n s were recorded in the experimental plots of the project on " I n t e g r a t e d N u t r i e n t Supply S y s t e m for S u s t a i n a b l e S u g a r c a n e P r o d u c t i o n " a n d " W e e d M a n a g e m e n t in S u g a r c a n e Based C r o p p i n g Systems". We thank our Director Dr N. B a l a s u n d a r a m for the facilities provided.

Singh, N.P., Verma, R.D.N., Singh, R.G. and Singh, S.B. (2000). Effect of plant geometry and nitrogen level on yield and juice quality of sugarcane. Sugar Tech, 2(1&2) : 40-43. Srikanth, J., Easwaramoorthy, S., Kurup, N.K. and Santhalakshmi, G. (1997). Spider abundance in sugarcane: impact of cultural practices, irrigation and post-harvest trash burning. Biol. Agric. Hort., 14 : 343-356.

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