Written by C D Mayee
2017 witnessed pink bollworm (PBW) attacks on cotton, especially in Maharashtra and also in Telangana, Andhra Pradesh and Karnataka. The infestation of this insect pest — whose larvae bore into cotton bolls through the lint fibre to feed on the seeds — happened during October, just when the crop was maturing and almost ready for its first-flush pickings, and further aggravated by unseasonal rains at that point.
The unfortunate part about this time’s PBW outbreak in Maharashtra was that farmers there had planted a record 42 lakh-plus hectares under cotton, encouraged by the previous year’s remunerative realisations. There have been many misleading reports since then, linking the infestation to Bt cotton technology. This article seeks to highlight the real reasons behind the PBW menace and possible solutions to address the same.
A major cause of bollworm attacks is the absence of crop rotation. Continuous planting of cotton year after year encourages breeding of the pest. The situation has been made worse this year, with around 15 per cent cotton area in Maharashtra sown under herbicide-tolerant hybrids not approved for commercial cultivation. Even with regard to approved F1 hybrids not containing the herbicide-tolerance gene, there are many cases of fly-by-night operators simply multiplying their F-2 seeds and selling these as Bt.
Complicating all this has been the large number of hybrids – over a thousand – of different durations with varying flowering and fruiting periods, ensuring continuous food availability to pests. Particularly dangerous is the practice of extending the cotton plant’s life cycle beyond January-February, to allow more flushes, by giving protective irrigation. The pest cycle does not get broken as a result. Also, since the Bt toxin levels are diluted beyond 120 days, the long-duration crop is more likely to succumb to pest multiplication.
One way to reduce pest susceptibility is to plant non-Bt cotton as “refugia” in the vicinity of the main Bt crop. But farmers, especially with small holdings, don’t want to lose land in growing non-Bt plants that can act as hosts for the bollworm insects. It is important to note here that PBW exclusively feed on cotton, unlike other bollworm insect species that also attack other crops such as pigeon-pea, sorghum and sunflower. Without cultivating non-Bt cotton as refugia, PBW is bound to develop resistance to Bt toxins over time, as has happened in Maharashtra. Incidentally, Gujarat, too, reported significant incidence of the pest in 2015 and 2016. But thanks to concerted efforts at crop management by farmers, government agencies and seed companies, the state has registered no major outbreak during this season.
It should be possible for stakeholders across the cotton value chain in Maharashtra also to undertake a similar coordinated campaign, involving continuous field monitoring as well as pre-cultivation and post-harvest stage measures. Cotton is sown in June-July after the onset of the monsoon. There is need to ensure that the previous crop is not just terminated by end-January or mid-February, but also its stalks be utilised for pellet making, fuel briquettes and other purposes. Given this year’s severe PBW outbreak, all fields must be given two deep ploughings in the coming summer, so as to destroy all crop residues and obtain the advantages of natural soil solarisation. This should be supplemented by installation of light/pheromone traps near cotton godowns, ginneries and market yards to attract post-season moths.
Further, it is necessary to discourage farmers from sowing any pre-monsoon crop, while allowing only recommended hybrids/varieties from companies with established R&D facilities — which can vouch for the trait purity of the Bt cotton being supplied — to be grown. Also, these should ideally be of 140-160 days duration and resistant to sucking pests. Planting of non-Bt cotton as refugia can be enforced by supplying these seeds not separately, but in the same bags that contain Bt seeds. The refugia-in-bags concept has already been tested for efficacy and must be permitted in the ensuing kharif season.
Field monitoring should involve installation of pheromone traps. The application of insecticides and Trichogramma or Bracon biocontrol agents could be initiated once the economic threshold level (ETL) of around 24 moths per trap is observed. For the first 80 days of the crop, no synthetic pyrethroid should be sprayed. Insecticides such as quinalphos or thiodicarb may be used in the early crop growth stages at the rate of 20ml and 20g per 10 litre of water, respectively. If the ETL is crossed during October-November, then chlorpyrifos (20 per cent emulsifiable concentrate) can be sprayed at 25ml or thiodicarb (74 per cent wettable powder) at 20g per 10 litre of water. No growth-promoting chemicals or even urea should be applied during the crop’s grand growth phase to prevent greenness and succulence of foliage that attracts the pest. Only when the crop has grown beyond 120 days towards November-December and pest incidence has crossed ETL should pyrethroids — fenvalerate (20 per cent EC) or cypermethrin (10 per cent EC) at 10ml per 10 litres of water — be used.
The development of resistance breakdown of Bt cotton to PBW is, no doubt, cause for concern. But it only underscores the importance of a long-term policy framework that supports research and allows new farm technologies into the market. Bt technology significantly transformed the fortunes of the cotton value chain. The experience of the last 15 years (2002-17) is testimony to its adoption even by small and marginal farmers. At its peak, Bt cotton was planted on 117 lakh hectares or a whopping 92 per cent of the country’s total area under the crop.
Any technology, though, gets obsolete with time and requiring replacement, including with upgraded versions. The second generation BG-II Bt cotton was introduced in India in 2006, four years after commercialisation of the original Bollgard technology. Isn’t it strange that the last 15 years has seen just one technology with an upgraded version being commercialised in the agri-biotech field? Bt cotton, moreover, targeted specific pests – namely, insects of the heliothis species. Just as pesticide sprays against cockroaches cannot really be effective on bugs or flies, the same applies to Bt technology vis-à-vis PBW or sucking insects.
While there’s no alternative to continuous focus on research and long-term policies supportive of new technologies with science-based evaluation (as opposed to ideology), the threat posed by PBW can be tackled in the short term through sustained campaign focusing on breaking the life cycle of the pest. The various measures suggested above should enable managing the pest problem, at least in the coming season or two.