Evaluation of insecticides and a natural product for their efficacy against shoot borer ( Conogethes punctiferalis Guen . ) ( Lepidoptera : Crambidae ) infesting ginger ( Zingiber officinale Rosc . )

Nine insecticides and a natural product were evaluated for their efficacy against shoot borer (Conogethes punctiferalis), a serious insect pest of ginger (Zingiber officinale) for two years. Pooled analysis of two years data indicated that chlorantraniliprole 0.01% was the best treatment with a mean pseudostem damage of 2.6% which was on par with flubendiamide 0.02% (4.1%), spinosad 0.0225% (6.5%) and cyantraniliprole 0.005% (8.8%), when sprayed at 15 day intervals during the second fortnight of July to the first fortnight of November. The trials indicated that that these low-risk insecticides and the natural product can be utilized for the management of C. punctiferalis in ginger with reduced risk to the environment.


Introduction
The shoot borer (Conogethes punctiferalis Guen.) (Lepidoptera: Crambidae), is the most serious insect pest on ginger (Zingiber officinale Rosc.), widely used as a spice and in traditional medicine across the world. The shoot borer occurs in tropical and sub-tropical countries and the larvae infest more than 65 species of plants belonging to different families (Devasahayam & Koya 2005). The larvae bore into pseudostems and feed on the growing shoots resulting in dead hearts. When more than 50% of the pseudostems are damaged in a clump, the yield is significantly affected (Koya et al. 1986); severe infestations can cause yield losses up to 25% (Nybe 2001). The present management strategy for C. punctiferalis includes spraying malathion 0.1% (Koya et al. 1988) or quinalphos 0.05% + Ozoneem 1500 ppm (3 ml L -1 ) (Mhonchumo et al. 2010). In spite of the serious nature of the pest, very few newly developed low-risk insecticide molecules and natural products have been screened against the pest. Trials were conducted with the objective of finding out safer insecticides and natural products for management of C. punctiferalis in ginger and the results are presented in this paper.

Location
The trials were carried out in the experimental farm of ICAR-Indian Institute of Spices Research at Peruvannamuzhi (11°35'0"N, 75°49'0"E) in Kozhikode District, Kerala during the crop seasons of 2015-16 and 2016-17. The average annual rainfall of the location ranged from 4300 to 5300 mm.

Experimental plot
Ginger (variety IISR-Rejatha) was grown in raised beds (3 × 1 m 2 ) as a rain-fed crop. A spacing of 25 cm was maintained between each clump. Each bed accommodated 40 clumps and the planting was carried out in June each year. All agronomic practices recommended by ICAR-IISR et al. (2015) were followed except plant protection measures to raise a healthy crop.

Treatments
The treatments included nine insecticides and a natural product and control with water spray ( Table 1). The trials were conducted in a randomized block design and a single bed served as a treatment. Each treatment was replicated three times. The plants were sprayed with the chemicals to the point of runoff using a high volume knapsack sprayer. The treatments were imposed at 15 days interval starting from the last week of July when the first symptom of pest infestation was observed on the tender leaves and were continued up to the first fortnight of November. The number of healthy and damaged shoots by the borer in each clump was recorded in the last week of November when the plants started drying after maturation. The data were subjected to arc sine transformation and means were separated by LSD, year-wise and pooled analysis for two years was also carried out.
The U.S. Environmental Protection Agency (2017) has classified chlorantraniliprole, spinosad and cyantraniliprole as reduced risk insecticides. In India, these insecticides including flubendiamide are categorised under low toxicity group with either green or blue labels. Spinosad (derived from the actinomycetes Saccharopolyspora spinosa) is considered as natural product and has been recommended for use in organic agriculture. Though various natural enemies have been recorded on C. punctiferalis in many crops, specific records on ginger are limited. The natural enemies recorded on the shoot borer infesting ginger include mermithid nematode, hymenopterous parasitoids and entomopathogenic nematodes that play an important role in the suppression of the pest in the field (Devasahayam 1996;Pervez et al. 2014) and hence use of low-risk insecticides in the ginger ecosystem is important. The findings of the present study show that the low-risk insecticides such as chlorantraniliprole, flubendiamide and cyantraniliprole and natural product such as spinosad would be ideal for developing integrated pest management strategies against C. punctiferalis in ginger.