Abstract: A field experiment was conducted in Sorapet, Pondicherry, Union Territory, India, to evaluate the efficacy of crude extracts of D. angustifolia against Earias vitella on rainfed cotton. D. angustifolia crude extracts drastically reduced the number of larvae similar to a neem product. The percentage of damaged squares and bolls was also reduced after consecutive sprays compared to untreated and endosulfan (controls).
INTRODUCTION
The potential yield loss worldwide due to weeds, diseases and pre-and post-harvest pests is estimated at 45% (Gwo-Chen, 1999). In India, on an average, 33% of crop loss occurs due to pests and diseases (Puri et al., 1999) and runs to an estimated Rs. 200 billion (Singh, 1999).
Spotted bollworm, Earias vitella Fab. is one among the severe pests in cotton crop. Its incidence varies between seasons and the feeding preferences. It is abundant in high rainfall areas. The pest attacks the crop from 35 to 110 days. First and second larval instars prefers for squares, followed by bolls and flowers. They bore into the growing shoots, buds, flowers and bolls. The attacked shoots wither, droop and ultimately die, and flowers and buds drop off. Infested bolls do not shed, open prematurely and the quality of the lint is spoiled. Pupation takes place in the bolls, impairing the development of bolls (Sharma et al., 2004; Vennila et al., 2005).
The genetic resistance of pest species, toxic residues in food produce, increasing costs of application, hazards from handling etc., (Martin et al., 2000) due to the indiscriminate use of chemical pesticides have increased the need for an effective alternative biocontrol method using botanicals with greater selectivity. Biologicals are safe to higher animals and environment, relatively specific in their mode of action and application, easy to access, locally available and cost effective (Karuppuchamy, 1999).
The effects of methanolic extracts of Azadirachta indica and Melia azedarach seeds affected the oviposition behaviour and egg hatchability of E. vitella (Gajmer et al., 2002).
Though chemical insecticides as well as biopesticides have been targeted towards the dreadful noctuid, Dodonaea angustifolia has not been screened for such pests either in the laboratory or in the field. The initial experiments conducted in the laboratory have proved that this plant is highly potential against controlling H. armigera (Subashini et al., 2004) and hence the field trials with target pest and non-target pests were carried out under field conditions (Malarvannan, 2004). This article would focus on the bio-efficacy of the crude extracts of Dodonaea against Earias vitella.
Dodonaea angustifolia, commonly known as hop bush, (Vernacular Tamil: Viraali or Vilaari) is a perennial shrub belonging to Sapindaceae. In Tamil Nadu, D. viscosa dominates at Pacchaimalai foot hills, Kolli hills, Servarayans etc., (Gamble, 1987).
MATERIALS AND METHODS
Plant Material-source
Leaves of Dodonaea angustifolia was collected from different parts
of Kolli Hills, Namakkal District, Tamil Nadu.
Extraction of Plant Material
The leaves of D. angustifolia were shade dried and powdered. One
kilogram each of powdered leaves was extracted successively using non-polar
to polar solvents viz., hexane, petroleum ether, chloroform, acetone and water
according to the standard procedures (Harborne, 1998). The crude extracts were
measured and used in desired concentrations for field trial.
Field Trial
A field experiment of Randomized Block Design (RBD) on rainfed cotton was
conducted in a farmer’s field at Sorapet, a small hamlet near the outskirts
of Pondicherry, Union Territory to test the crude extracts of D. angustifolia
against Earias vitella. Individual plots were of 12 m2
size. Ten percent crude extracts (hexane, petroleum ether, chloroform, acetone
and water) of D. angustifolia were sprayed during the late hours of the
day using a knapsack sprayer. Neem product and endosulfan was used as positive
controls. Unsprayed plots were maintained as negative control. Six sprays were
given at weekly intervals. The pre treatment count and post treatment count
on number of larvae per plant and the damaged squares and bolls per plant were
taken (Fig. 1).
| Fig. 1: | Earias vitella incidence and damage on cotton before spray. a and b: Split squares and damaged bolls; c: Earias vitella larva; d: Damaged kapas; e: Larvae feeding and f: Severely damaged boll |
RESULTS AND DISCUSSION
Number of Larvae
The number of larvae (Table 1) drastically reduced in
all the extract treated plots along with neem product. Most of the treatments
resulted in nil larvae after 2nd spray, however larvae were seen in chemical
treated and untreated plots until the last spray.
Damaged Squares and Bolls
There was 50% reduction in percent damage squares after 1st spray, compared
to before spray and there was no significant difference among the treatments
even after 2nd spray. Further, plots treated with Dodonaea extracts showed
less percent of damaged squares and bolls, which was on par with neem product
(Table 2 and Fig. 2).
| Table 1: | Effect of D. angustifolia extracts against Earias vitella larva on cotton |
| Each value mean of triplicate of mean of five plants/plot, NS: Non Significant; Different letter(s) in each column differ significantly (5%) by DMRT | |
| Fig. 2: | Earias vitella incidence and damage after Dodonaea spray. a: Less split squares and bolls; b: Undamaged flower; c: Reduced damage-field view and d and e: Retrieval of affected field-less damaged squares |
| Table 2: | Effect of D. angustifolia extracts against Earias vitella on cotton field |
| Each value mean of triplicate with mean of five plants/plot, NS: Non Significant; Different letter(s) in each column differ significantly (5%) by DMRT | |
This is in accordance with the findings of Samuthiravelu and David (1991) who found that applications of neem oil and endosulfan, alone and together, reduced damage by Earias vitella on lady’s finger and by Dhawan et al. (1992) in upland cotton.
CONCLUSIONS
The experimental results prove that such less explored plants do have a potential to combat pests in an ecofriendly way and would serve as promising biopesticides, if handled at right combination and dosage at the right time.
ACKNOWLEDGMENTS
The authors acknowledge the Sir Dorabji Tata Trust, Mumbai for the financial support and the farmers of Sorapet who helped us to conduct the experiment without any hindrance. Thanks are due to Mr. S. Anand former staff of MSSRF who helped us in the selection of suitable field and to staff of Kolli hills in the collection of plant material.