Insecticide Resistance Management Strategies For Cotton Pests

By   Dr. K. R. Kranthi
Central Institute for Cotton Research (ICAR), Nagpur.

In intensive agriculture, insecticides have been looked upon as omnipotent weapons for modern pest management. Excessive and indiscriminate use of insecticides in cotton has led to problems of insecticide resistance, pest resurgence, accumulation of harmful residues and toxicity to non-target organisms. This has prompted the necessity for the development of non-insecticidal alternatives that could be feasible and effective for insect pest management, while also being compatible with the environment. Resistance to insecticides reduces the effective window for insecticides to achieve economic control of Helicoverpa armigera, hence, the choice of effective insecticide is imperative if pest control has to be efficient. Keeping in view the results of the current study and the existing information on cotton pest management , a `window strategy’ for cotton pest management is proposed with specific emphasis on the management of insecticide resistance in H.armigera. Primarily, the insecticide resistance management (IRM) strategies aim to at least slow down the resistance treadmill, thereby extending the usefulness of available chemicals. Successful IRM is not just a clever re-organization of chemical countermeasures into mixture and/or rotation schemes. IRM strategies must complement good Integrated Pest Management (IPM) practices and only when IRM is properly incorporated into acceptable IPM programmes will there be any hope of successful resistance management Integrated Pest Management approaches incorporated all approaches to ensure favourable ecological, economical and sociological consequences. But, a number of strategies have either been inaccessible or complicated. This bulletin suggests some simple pest management strategies for India based on the results from studies on monitoring, resistance, mechanisms, and insecticide resistance management, that can enable low-cost approaches for a sustainable and better insect pest management.

COTTON PESTS

The cotton bollworm Helicoverpa armigera, pink bollworm Pectinophora gossypiella, tobacco caterpillar Spodoptera litura, whitefly Bemisia tabaci and Jassids Empoasca devastans are some of the major pests of cotton that have the potential to reduce yields by 20-80% Harmigera has been reported (Manjunath et al, 1985) to feed on 181 cultivated and uncultivated plant species. It is known to cause economic losses to cotton, pigeonpea, chickpea, tomato and sunflower. The total losses to chickpea and pigeonpea together were estimated to exceed U.S. $300 million in some years. Though sporadic reports (Kaushik et al, 1969; Manjunath, 1974) mentioned economic losses in cotton pest in India till early eighties. Text books of Entomology (Lefroy, 1906; Fletcher, 1914; Nair, 1975; Atwal, 1976) if at all, refer to this insect as a pest of minor importance to cotton. In Southern India, the tobacco caterpillar Spodoptera litura (F) and the spotted and spiny bollworms, Earias vitella (F) and E.insulana(Boisd).were the major cotton pests till 1983 (Agarwal and Gupta, 1983). It is not known if the introduction of synthetic pyrethroids in 1982-83 cropping season was the main cause, but within the subsequent two years, H.armigera and the whitefly, Bemisia tabaci (Gemm.) emerged as the major pests in place of the earlier species H.armigera is now the dominant pest of cotton and pulses in almost all regions of the country.

Insecticide Resistance – Current Status in India

Resistance to insecticides was monitored either through Discriminating dose assays (use of a single dose that kills 99% individuals of a susceptible strain) to indicate per cent resistant individuals in a field population or through log dose probit assays to derive the LD50 of the field population is then compared to that of the susceptible strain and expressed as resistance in x fold. Resistance to pyrethriods continues to be high with levels of 108 to 7220 fold in almost all parts of the country. Earlier Armes et al., (1996) had reported resistance factors of 5-6500 fold to pyrethroids in field populations of Helicoverpa collected from all parts of the country. Pyrethroild resistance is wide spread in India, at high levels in Maharashtra, Punjab, AP and Tamilnadu Resistance levels during the entire season are usually high with minor exceptions during early season are usually high with minor exceptions during early cotton season and appear to be independent of the pyrethroid use pattern (Kranthi et al., 1997). The problem is still most severe in the coastal belt of AP. When used alone pyrethroids are no longer expected to be effective against Helicoverpa except on larvae less than second in star stage. However, resistance assays carried out against the pink bollworm and spotted bollworm indicated that these were still susceptible to pyrethroids. Pyrethroid resistance levels during 1993-99 have been high all over India. In most parts of the country, survival frequencies to the discriminating dose of cypermethrin 0.1 m g are still found to be 95-100%. Despite the steady decline in the preference for pyrethroids in cotton pest management over the past two-three years, resistance to pyrethroids does not appear to be on the decline. The `93-‘99 data on `in-season’ changes in pyrethroid resistance at all centres, however, indicates that resistance levels were relatively lower during the cotton season (October-November for A.P.,Coimbatore, and Maharashtra and August-September for North). This information supports the idea that pyrethroids could still be used on cotton against Helicoverpa infestation during the period mentioned above. This could as well be meaningful for better utilization of these compounds as the pyrethroid application during this time also coincides with the early infestation of the pink bollworm.

Resistance to Endosulfan was found to be 1-14 fold in the field populations tested. Armes et al., (1996) had reported resistance factors of 2-28 fold and suggested that field control failures could be caused due to resistance factors as low as 5-10 fold. Seasonal averages of resistance to endosulfan have been very high throughout ‘93-99 at Coimbatore (45-57%), Guntur (47-67%) and Nagpur (40-46%), but relatively low in Rangareddy district (29-35%) and parts of Punjab and Haryana (15-20%). However a closer look at the dynamics of resistance for all season of ‘93-99’ reveals that, at all the monitoring sites (except Coimbatore), resistance to endosulfan has been low (20-25%) at the beginning of cropping season and generally increases to about 40-50% by the end of November when spraying on cotton ceases. At Coimbatore resistance to endosulfan appears stable at about 45-50% (with minor exceptions) throughout the season during all the years. Hence endosulfan is being recommended as an early season insecticide.

Resistance to quinalphos was found to be low to moderate at 1-29 fold,, for the field populations collected recently during ‘98-‘99. Resistance was higher in the coastal belt of Andhra Pradesh and some pockets of Central India. Earlier quinalphos resistance has not been reported to exceed 2-9 fold in field populations (Armes et al., 1996). Resistance to quinalphos has been high at Guntur (45-66%) and Coimbatore (44-48%), but low (about 20-25%) in Punjab, Rangareddy and Nagpur. It was also observed that resistance levels to OPs and endosulfan increase in the season depending on the use of these compounds. Organophosphates such as quinalphos, chlorpyriphos and profenophos can be used during the peak reproductive phase of the crop.

Resistance to methomyl was 1-22 fold, with higher levels in the coastal belt of Andhra Pradesh and some parts of Central India. Resistance to methomyl was monitored at all sites (except Coimbatore) during `97-99’ seasons. Resistance appears to be gradually on the rise with recent increase in the use of this chemical for Helicoverpa control. Resistance increases were similar to that of organophosphates, for example resistance was moderate (31-40%) in September, October and December but increased later to 69% in February. Armes et al, (1996) report resistance levels of 2-38 fold to methomyl in different parts of India, with highest at 162 fold in Guntur. The carbamates can be used as a single spray prior to the pyrethroid window.

IRM Strategies

Formulating resistance management strategies for Indian conditions has been fairly complicated. The diversity and complexity of cotton farmers, cultivation practices and cropping situations has always posed a challenge. The strategies need to be uncomplicated, simple, robust, available, affordable, compatible with current cropping practices, easy to understand, etc. Most IPM proponents would now agree that some of the biological intervention components of cotton IPM have been tricky due to their inconsistency in performance and importantly their non-availability. Insecticides in most situations have usually been found to be counterproductive due to resistance and resurgence problems. The current strategies hence blend all crop production practices to incorporate proper use of insecticides to ensure that each of these groups are applied at such time of the cropping phase when

1. Resistance is low

2. Natural enemy populations are least disturbed and

3. Different group of chemicals are alternated.

Selection of cultivar for Central & South India

Recommended hybrids: NHH-44, PKV HY-2, JK Hy-1, JK Hy-2, H-8,H-10, Ankur-651

Recommended varieties: LRA-5166, LRK-516, PKV-081,

Desi types: AKH-4, AKH-8401

Selection of cultivar for North India:

Early maturing: F-846, F-1378, LH-1556,F-2054, H-1098

Recommended hybrids: Omshankar, Fateh, Dhanalaxmi

For CLCV prone areas: RS-875, LHH-144, LRK-516,LRA-5166. All desi types (LD 327, HD-107, LD-491)

Resistant/tolerant to jassids : Bikaneri Narma, H-777, RS-875, RST-9, F-5-5, Fateh.

Cultivation Practices Optimised for Better Pest Management

• Hybrids must be grown in medium – deep soils having good drainage.

• Early sowing on ridges and furrows, especially in areas with drip facility, could be adopted.

• Application of weedicide Stomp 30EC or Basalin @ 45EC 2.5 lt/ha and harrow immediately to prevent degradation.

• Harrowing must be done twice after pre-monsoon showers and field should be levelled.

• Prepare a good seed bed to ensure good plant stand.

• Grow only arboreum cotton in CLCV hot-spot areas.

• Only recommended varieties/hybrids from reliable sources must be procured.

• Apply 10-15 cartloads of well decomposed compost or FYM/ha before sowing.

• In North, sowing can be done at a row spacing of 67.5 cm with 30 cm plant-plant spacing or preferably wider for varieties and 75 cm for hybrids. In South and Central zones sowing can be done at a row spacing of 90 cm with 60 cm plant-plant spacing for hybrids, 60 x 30 cm for varieties and 45 x 20 for Desi cultivars.

• Fertilizers should be applied @ NPK 60:30:30 for varieties and 90:45:45 for hybrids under rainfed situation. For irrigated cotton NPK should be applied at 90:45:45 for varieties and 120:60:60 kg/ha for hybrids. Fertilizer should be given in three splits, the last to be given before boll-set.

• In Central and South India sowing must be completed by the first week of July. In North India it is preferable to complete sowing operations by the third week of May.

• Gap filling must be completed within 10 days after sowing.

• Thinning should be done within 20 days after sowing.

• First hoeing can be done 30-40 days after sowing followed by second after 15-20 days.

• Cowpea can be sown either as bund crop or intercrop and has been found source to natural enemies of sucking pests, which also assist in keeping sucking pests of cotton in check.

• Do not stack cotton stalks near fields.

• Immediately after the season allow animal grazing in fields and ensure timely removal and destruction of cotton stubbles, followed by deep ploughing to expose the carry-over population of bollworms.

• Delint the seed with 100 ml sulphuric acid/kg seed for two minutes, wash with water and soak for two minutes in sodium bicarbonate (5g/ltr water).

• Treat seeds with Ceresan wet or Agallol @ 1 g/ltr water

• Treat seeds with Captan or carbendazim @ 2g/kg.

• Destroy weeds such as Datura metel and Legascea mollis near fields. These support Helicoverpa populations during off-season. Destroy weeds such as Sida, Abutilon and Xanthium before sowing to reduce CLCV incidence.

• Avoid growing American cotton in orchards.

• Avoid growing tur, moong and bhendi (Ladies finger) in and around cotton field as these harbour insect pests.

• Crushing of cotton seeds should be completed by end of April, or fumigate seeds with celphos @ 3g/cubic meter.

Vegetative Phase

• Seed treatment (Carbosulfan 50g/kg seed) also helps in delaying the first spray (Imidacloprid 7g/kg seed was found useful for hybrids in protecting the crop against Jassids upto 40-60 days).

• Grow sucking pest tolerant genotypes. It helps in delaying the first spray, thus conserving the initial build-up of natural enemies. Some Jassid tolerant cultivars need not be treated with insecticides and are capable of protecting themselves from sucking pests. It is possible to avoid spraying for at least two months for some susceptible genotypes treated with Imidacloprid or carbosulfan.

• Jassids and Aphids cause maximum damage during vegetative period of the crop. But, populations of Lady bird beetles, Syrphids and Chrysoperla carnea are also generally high and assist in reducing the pest load.

• Do not use broad spectrum insecticides such as phosphomidon, dimethoate, monocrotophos, metasystox, accephate or any other insecticides belonging to the organophosphate group, as they strongly disrupt natural enemy populations. Avoidance of organophosphate insecticides for the first three months helps in build-up of entomophage populations such as Chrysoperla, Campoletis chloridae, Microchilonis curvimaculatus, Tachinids, Apanteles, Orius spp. And Podisus spp., bugs, etc., which contribute to the management of Helicoverpa.

• Do not use any insecticide except NSKE + neem oil or endosulfan (as emergency option against jassids at 2/leaf, and aphids 50/leaf) against jassids or aphids within three months of sowing. Helicoverpa incidence can be noticed in late vegetative phase of the crop in some fields, but the infestation is very low and sporadic and does not warrant intervention.

Early Reproductive Phase

• Spotted bollworm can cause damage to growing points in Central and South India, but does not cause economic losses. However, pink and spotted bollworms are important pests in north and need to be managed. Set up pheromone traps @ 5/ha for pink bollworm in North India. Eight moths/trap/night for the three consecutive nights is the action threshold.

• Do not use any unregistered compounds such as botanical extracts, neem formulations, etc. It is better to use neem oil or aqueous extracts of 25 Kg neem seed kernel/ha, instead of any commercial formulations.

• Helicoverpa incidence starts in this period. Scouting must be done in at least 50 plants per hectare. Thresholds of 25 larvae/50 plants should be considered for spray of endosulfan.

• Use of endosulfan should be encouraged only as early season spray against Helicoverpa armigera as resistance levels have been found to be invariably low early in the season. Endosulfan is also relatively less toxic to natural enemies.

• In North India, pyrethroids may be used as initial sprays, if Helicoverpa egg populations @ more than one egg per plant is also noticed simultaneously along with an attack of spotted and pink bollworm. It would be advisable to take up not more than one application of pyrethroid before mid-September. Pyrethroids have strong contact action on all lepidopteran moths; are effective on younger larvae and are ineffective after mid-September due to increase in resistance levels and also due to presence of all stages of larvae. It is advisable to add 1 litre/ha of Sesamum oil to pyrethroids as it helps in counteracting resistance. Sesamum oil should never be mixed with any other group of insecticides.

• Pyrethroids should be used only once. Synthetic pyrethroids either as over dose or repeated sprays leads to excessive whitefly flareup.

• Set up Pheromote traps @ 5/ha for H.armigera to identify brood emergence.

• It has been found useful to spray 2% DAP at 80-90 days after sowing.

Peak Reproductive Phase

• American bollworm causes maximum damage during peak reproductive phase

• Resistance levels against certain organophosphate group of insecticides (Quinalphos, Chlorpyriphos and Profenophos) and carbamates such as thiodicarb have been found to be relatively lower in most populations tested. Hence, it is preferably to use these as effective larvicides during mid-season (Aug-Sept for North and Sept-Oct for Central and South India) based on ETLs (20 larvae/20 plants) when the situation warrants.

• Pyrethroid resistance is high in many parts of India. However, pyrethroids are still effective against spotted and pink bollworm. In South and Central zones pyrethroids can be used after second week of October to target Helicoverpa and a simultaneous initial infestation of the pink bollworms.

• Pink bollworm infestations are usually high during November in South and Central zones, but are rarely noticed by farmers. It is advisable to use one application of any pyrethroid at a threshold level of 8 moths/trap/night for the three consecutive nights in pheromone traps. It must be remembered that pheromone septa need to be changed once a fortnight.

• In South and Central zones during outbreak years, Helicoverpa may persist till second week of November sometimes. Based on thresholds of 20 larvae/20 plants/acre,carbamate insecticides such as Thiodicarb may be used during this period.

• In Andhra Pradesh, egg batches of Spodoptera must be handpicked. Light traps are very effective in Spodoptera management and must be used. Other strategies such as SNPV can also be deployed for effective management of Spondoptera.

• Insecticides such as monocrotophos are not effective against either Helicoverpa or Spondoptera and must be avoided either alone or as mixtures.

Some General Strategies of IRM

• Handpicking of larvae 2-3 days after insecticide sprays effectively eliminates any surviving population which can cause future resistance problems.

• Always use insecticides as need based applications as per threshold levels. The keys to obtain better result from the use of insecticides are :

1. Right time-use insecticides –only when the need arises

2. Right chemical-choose-appropriate insecticide

3. Right dosage-use-only recommended dose.

4. Right method-use-proper sprayers and spray methods.

• Always target younger stages of Helicoverpa as younger stages of resistant larvae are known to get killed at normal recommended doses.

• Rotation of chemical groups helps in preventing the build up of resistance against most insecticides, especially carbamates, organophosphates and endosulfan.

IRM Strategies for Cotton Pest Management in Northern India: