PLANT RESPONSES TO LATE SEASON WATER DEFICITS IN ACALA COTTON CULTIVARS

Abstract                                                                       Back to Table of contents

Continued development of irrigation strategies that minimize crop yield losses, while increasing water use efficiency are needed in many semi-arid and arid cotton producing areas world wide.  Controlled deficit irrigation (CDI) incorporates the knowledge of crop physiology and phenology to identify specific plant growth stages in which water deficits have a minimal impact on crop yield and quality.  Previous research in California and other irrigated agricultural regions have documented the severe yield impact when moderate early season water stress is allowed to accumulate in cotton (Gossypium hirsutum L.).  Conversely, similar late season water stress following plant cutout has had a minimal impact on crop yield and quality.  This paper is a report of recent studies that were undertaken in an effort to apply the concepts of CDI for cotton (Gossypium hirsutum L.) and suggest approaches to farm water managers which enable a greater understanding of deficit irrigation strategies.  Studies conducted in the San Joaquin Valley of California from 1991 to 1993 have consistently demonstrated that high yields can be obtained although late season water deficits in cotton were present.  The optimum timing of the final in-season irrigation for cotton was shown to be dependent on the cultivar.  The determinant plant types tended to have more significant yield reductions as water stress is increased following plant cutout, while the indeterminate types were found to be less sensitive to the timing of late season water stress.  The timing of late season water directly alters the stress accumulated in the crop thereby impacting late season boll retention, boll maturation and crop yield.

Conclusions 

The monitoring of cotton plant performance characteristics following periods of induced late season water stress can assist in developing deficit irrigation management strategies.  To date, very little information is available regarding modern cotton cultivators and their tolerance to late season water stress.  By varying the degree and timing of water stress accumulation, we can begin to recognize both general trends for timing the final irrigation and select varieties that suit an individual field managers needs with respect to timing the final irrigation.    Moderate plant water stress induced late in the season, can reduce consumptive water use without severely impacting on crop yield or quality.  The decision of when to time the final irrigation for cotton, is dependent upon the variety and the degree of water deficits.  Delayed scheduling of late season water is preferred for more indeterminate plant types resulting from their improved tolerance to water deficits.  Shorter season, more determinant plant types, experienced significant yield reductions when moderate late season water stress was allowed to build.  The preferred irrigation strategies for determinant varieties would therefore favor the deliver of available water supplies prior to the development of moderate water stress levels (-21 bars).

The pressure chamber can be an effective tool in evaluating the intensity and duration of cotton water stress.  Generally, plants performed well with highest yields obtained when LWP readings were not allowed to exceed -23 bars.  Significant impacts on plant growth and fruit retention were observed when LWP readings were allowed to reach the wilting point of -30 bars.  At these high water stress levels, decreases in transpiration rate and photosynthesis are likely causes of delayed fruit set and hence the production of unharvestable late season bolls.  The production of these late season bolls, although not equivalent to the lost production of lower fruiting positions, does demonstrate a resiliency of cotton to partially recover from severe water stress levels.

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CONTROLLED ENVIRONMENT STUDY OF THE DEGRADATION OF ENDOSULFAN IN SOILS

Abstract                                                                         Back to Table of contents

The degradation rate of endosulfan applied to a Black Earth soil from South East Queensland, was studied in controlled environment chambers. The degradation rates of a- and b-endosulfan were determined for the soil samples kept at the constant temperature of 30˚C under two water contents of 20% and 30% and submerged under water. The degradation rates of both isomers in all three moisture conditions followed first order kinetics with the rate constants differing significantly between submerged and non-submerged soils. For non-submerged soils the degradation rates of the two endosulfan isomers were lower for the soil with higher water content. The b-endosulfan isomer disappeared from the samples at a faster rate than the a-isomer at both water potentials. However the rates of decline for both isomers were much slower than those suggested in the literature.

Degradation of both endosulfan isomers in the submerged soil took place at a slower rate than in the non-submerged conditions, and in contrast to the results with unsaturated soil, the rate for b-endosulfan was slower than the a-isomer. Adding endosulfan to soil appears to reduce the rate of degradation of other organochlorine pesticides already present in the soil. The half-life of dieldrin was significantly increased in the presence of endosulfan. This effect was much more pronounced at the higher of the two water contents investigated. The applicability of these results to the soils of cotton farms in Queensland and NSW is under investigation.

Conclusion

Degradation of sorbed endosulfan at constant temperature appears to be well described by a first order kinetics equation under every moisture condition studied. In the soil studied, the degradation rates for both endosulfan isomers, however, are much slower than expected from the literature, half-lives being comparable with those of the most persistent members of the organochlorine family of pesticides. The main reason for such longer-than expected half lives could be the low pH value of the soil used in the experiments. It may be noted that in Australia, though not necessarily elsewhere, cotton soils have a high pH.

The degradation rates of both a- and b-endosulfan in the moist (non-submerged) soils were affected by soil moisture content, both rate constants being smaller for 30% water content than 20%. This effect was more pronounced for a-endosulfan than the b-isomer.  Similar effects of water content were observed for aldrin and dieldrin present in the soil. Combining these results with those given by Ghadiri et al. (1995) suggests that the soil water content of around 20% (-220 kPa potential) may be the optimum moisture condition for the degradation of endosulfan and other organochlorine pesticides studied. The degradation of all these pesticides decrease when the soil is wetter or drier than this optimum value.

When submerged under a deep layer of water, the degradation of b-endosulfan in soil is significantly slower than in the non-submerged condition, while the reverse was true for the a-isomer. Such an unexpected behaviour of the endosulfan isomers in the submerged soil necessitates further studies of these chemicals in the bedloads of the rivers and lakes which receive agricultural runoff.

A negative interaction was observed between the newly applied endosulfan and other organochlorine pesticides already in the soil. Applying endosulfan to the soil containing aldrin and dieldrin reduced the rate of degradation of the latter two pesticides. Interactions of this type could become an important factor in predicting the degradation rates and the half-lives of a various sorbed pesticide added to the soil. Interaction of similar nature might have contributed to the persistence of DDT and DDE in the cotton soils of Australia several years after their final application.

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FUTURE ROLE OF COTTON RESEARCH IN DEVELOPING COUNTRIES

Introduction                                                                Back to Table of contents

Cotton is of major importance in the economies of developing countries.  It has a major impact in the agricultural, industrial, transport and service sectors of over twenty developing countries and a significant impact likewise in some fifty others.  Cotton contributes to the economies of developing countries in many ways.  It generates employment in agriculture and industry, it earns critical amounts of foreign exchange as an export crop, it produces the raw material for indigenous textile industries, and it is a source of fibre, food and fodder.  Developing countries are today responsible for some 80% of the world’s supply of cotton, estimated at 18 million tons in 1993/94, grown on about 33 million hectares of land and with a total value of $30 billion…

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An Integrated Cotton Insect Pest Management System for Cotton-wheat Intercropping in North China

Abstract                                                                         Back to Table of contents

The north China cotton region is the largest cotton-producing area in China, with 3.5 million hectares grown to cotton annually, which constitutes 65% of the nation’s total cotton land. Since the 1980s, there has been a rapid expansion of cotton-wheat intercropping, with the double cropped acreage increasing from 0.4 million hectares in 1978 to 2.3 million hectares in 1993, now accounting for 65% of the region’s total cotton area. Because of this dramatic changes in the cropping systems, structures of insect communities and the dynamics of major insect populations have been altered. Thus, new control strategies and techniques must be developed.

During 1990-1993, structures of insect communities, fluctuations of major insect populations and control techniques in cotton-wheat intercropped areas, were studied. Based on these and previous studies, an integrated insect pest management (IPM) system for cotton-wheat intercropping in north China was developed. The IPM system comprised of four sub-systems; the technical, monitoring, decision-making and extension. The technical sub-system was the major component and consisted of a technical strategy and control techniques. The technical strategy was defined as “suppression of early and late season insect pests through bio-ecological regulating techniques and control of those at mid-season by rational application of insecticides”. The control techniques for the early season were habitat modification, cultivation of early maturing cultivars and conservation of beneficials; those for the mid-season were trapping and chemical control; and those for the late season were application of plant growth regulators, removal of insect food sources and application of selective insecticides.

The IPM system was demonstrated and extended areawide in the major cotton producing provinces of Shandong and Henan during 1991-1993, which brought about significant economic, social and ecological benefits.

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DEVELOPMENT OF AN INSECT SPECIFIC FUNGUS (NATURALIS–L®) FOR CONTROL OF COTTON INSECTS

Abstract                                                                         Back to Table of contents

The insect specific fungus, Beauveria bassiana (Balsamo) Vuillemin, ATCC 74040, formulated as Naturalis–L®, was highly effective for control of cotton insects in an integrated pest management system (IPM) for cotton in the Lower Rio Grande Valley of Texas. Naturalis–L® effectively controlled  populations of the boll weevil Anthonomus grandis Boheman, cotton fleahopper Pseudatomoscelis seriatus (Reuter) and silverleaf whitefly Bemisia argentifolii. Naturalis–L® was effective as an ovicide and as a larvicide on the tobacco budworm Heliothis virescens (F.) and the bollworm Helicoverpa zea (Boddie).  Population of beneficials was significantly higher in cotton fields treated with Naturalis–L® than in fields treated with conventional insecticides.  Full season control of insects was obtained in fields treated with Naturalis–L® only and in Naturalis–L®/IPM programs. Lint yields were equal to or better than yields of cotton  fields treated with conventional insecticides.

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NOVEL BIOLOGICAL AND CONVENTIONAL INSECTICIDES: WHAT’S NEW?

Abstract                                                                         Back to Table of contents

In recent years, with the continuing burden of increasing development and registration costs, the agricultural community has been facing the loss of a number of products from its portfolio of insecticides.  Furthermore, as different governments enact upgrades to their regulatory procedures or bring in tough new re-registration laws, there will be additional pressure on minor products that fit niche markets and specialty use opportunities, some of which are of significant importance to cotton growers.  This trend affects the whole agricultural industry, but is particularly noticeable in cotton where perhaps the broadest range of products is used on a wide variety of pests in cotton producing countries around the world.

It is encouraging, therefore, to see that despite the increasing costs that the multi-national agricultural chemical companies are incurring to support their international registrations, there has not been a time in recent years when so many new insecticide developments are finding their way into the hands of the cotton grower.  These new developments cover new chemistries with novel modes of action, both contact and systemic, such as the nicotinyls, pyrroles, phenyl pyrazoles, amino triazinones and the quinazolines.  In addition there are several new insect growth regulator products, both benzoyl phenyl ureas as well as novel structures, hormone analogs and a range of new products and improvements in the field of biologicals and natural products. In terms of resistance management, such developments could not come at a better time to fit into integrated programs around the world.  Some of these new products will undoubtedly find utility in helping overcome control problems due to resistance.

These new developments, from a wide variety of agricultural chemical companies, and their potential for the control of various pests around the world, are reviewed.  Opportunities that some of these discoveries might offer in terms of resistance management are also discussed.

Conclusion

It is clear from the above that there is significant potential for the expansion of the global arsenal of new insecticide products.  Not all the products discussed will end up with cotton registrations in all or even some countries.  Different governments regulate the registration of new pesticides in different ways, thus certain products may mature with disjointed use patterns on a global basis.  Some others, such as the new chemistries that possess novel modes of action, may very well obtain registration in all the major cotton markets.  Most of the products discussed will find great utility in the handling of resistance concerns, adding new opportunities for the development of more effective management programs.

After the paucity of new developments over the last decade, we are entering into an exciting future of integrated pest control that bodes well for the long term survival of global agriculture.

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THE BREAKDOWN OF LAMBDA-CYHALOTHRIN IN COTTON GROWING SOIL

Abstract                                                                         Back to Table of contents

The breakdown of lambda-cyhalothrin in cotton growing soil was studied in an indoor incubation experiment. Lambda-cyhalothrin was incubated at 30˚C in the dark in soil with different water contents. The degradation rate was similar at three water contents ranging from 30% to 90%. Degradation in shaken aqueous soil slurry was faster than in unsaturated soil, possibly due to the better redistribution of the lambda-cyhalothrin. The study indicated that degradation of this compound followed first-order kinetics and the half-life of this compound in different soil water contents was calculated to be in the range of 19-37 days. Degradation was apparently biological, as it was prevented by heat sterilisation and sodium azide. The isomerization of lambda-cyhalothrin also occurred in this experiment.

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COTTON PEST CONTROL PROBLEMS IN ANDHRA PRADESH, INDIA: OPTIMISING PEST MANAGEMENT OPTIONS FOR A MORE SUSTAINABLE APPROACH TO COTTON CULTIVATION

Abstract                                                                         Back to Table of contents

Changes in the field effectiveness of insecticides for control of cotton pests in Guntur district, Andhra Pradesh, India for the period 1979-92 are documented. Since 1985, cotton yields have decreased largely as a result of over dependence on insecticides for pest management resulting in resurgence of whitefly, Bemisia tabaci, and the development of insecticide resistance in the cotton bollworm, Helicoverpa armigera. Experiments are described where it is shown that intercropping cotton with short duration legumes or fox-tail millet (Setaria italica), results in higher cotton yields than sole cotton with the benefit of additional yield from the intercrop. An integrated pest management (IPM) strategy was evaluated alongside standard farmer practice for cotton production in Guntur district and in two seasons, significantly higher yields were recorded in the IPM treatment where only five insecticide applications were made compared to the 23 applications for the farmer practice treatment.

Conclusions

The results presented in this paper show that many of  the insect pest problems encountered in cotton crops in Guntur district, Andhra Pradesh, can be attributed to risk averse farmers over-using insecticides. Pyrethroid, organochlorine and organophosphate insecticides are now far less effective against cotton pests than they were in the early 1980s. This is largely a result of development of insecticide resistance in the major cotton pest, H. armigera and resurgence in the sucking pest complex, some of which may also be resistant to insecticides but this has not been tested in India to date.

The simple IPM trials outlined in this paper clearly show that by enhancing natural enemies in the cotton cropping system through intercropping, reduced conventional insecticide inputs and improved agronomic practices, higher cotton yields can result. Farmers would also benefit from reduced costs associated with the purchase and application of pesticides which, under current  practice, are applied at least once per week and frequently up to three times per week.

The next stage of this research will be to undertake similar trials in farmers’ fields to demonstrate the benefits of IPM and encourage farmers to adopt similar practices.

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ECOLOGICAL ATTRIBUTES OF MAJOR COTTON PESTS: IMPLICATIONS FOR MANAGEMENT

Abstract                                                                         Back to Table of contents

Integrated pest management (IPM) should be based on sound ecological principles. It requires knowledge of the interaction between the fauna (pests and their natural enemies) and its environment.  This paper attempts to review some of the interactions between pests and the cotton agroecosystem.

The pests considered are: pink bollworm (Pectinophora gossypiella Saund.), the Heliothis/Helicoverpa complex, sweet potato whitefly (Bemisia tabaci Genn.), cotton aphid (Aphis gossypii Glover) and boll weevil (Anthonomus grandis Boh.). Ecological attributes that are of significance to pest management are discussed. They include: adaptation to adverse conditions through diapause, search for suitable host plants through dispersal and migration; reproduction and the role of pheromones, growth and development in relation to climate and the presence of wild and cultivated hosts; and natural enemies (insects and pathogens).

The second part concerns the ecology of cotton-based farming systems. Pest control strategies should be based on a clear understanding of the growth and development pattern of cotton;  of other crops that are grown before and after a cotton crop or in its vicinity; and of local wild plant species. Weather and climate have to be considered for selecting the site,  planting dates, cultivars, and mode of application of plant growth regulators.  Fertilizers can affect  growth and development of certain pests also. Management of crop residues is a key factor that influences survival of overwintering species.

The ability of pests to counter individual control measures underscores the importance of developing a larger arsenal of crop protection techniques based on crop and pest ecology. A multidisciplinary approach offers the only possibility of anticipating the consequences of disruptive practices, such as change in cultivars and cultural practices, in the same way as efforts to counter the non-intentional effects of pesticide applications.

Conclusion 

Pest control requires knowledge of ecological principles. All possible factors, both natural and artificial, that could be used to combat crop pests must be considered. We cannot disregard the capability of pests to counter control strategies. Hence, IPM requires the forming of teams of scientists capable of taking a broad ecological overview of the pest problems associated with the cotton agroecosystem and willing to develop unified, ecologically based approaches to cotton pest control. Only such multi-disciplinary teams will have the potential for developing effective, economical and sustainable solutions for cotton pest problems, by approaching the cropping system as an ecological unit.

IPM strategies remain conditioned by our limited understanding of the biology of the pests, their mobility and interactions, and the shifting germplasm of the cotton crop. A holistic approach provides new insight into the complexity of interspecific relationships of arthropods in the agroecosystem; the major natural enemies and other factors that determine the abundance of key, occasional and potential pests.

The forming of teams whose members include specialists in crop protection and other disciplines should prevent the emergence of ‘single answer’ control measures. An IPM approach will provide alternative solutions in the event of ‘crises’, such as the emergence of pesticide-resistant strains, biotypes that overcome plant-resistance traits or the arrival of a new species in an ecosystem.

Cotton insect management problems observed recently in various parts of the world, would probably be a good illustration of these principles. It appears that the areas concerned are located either in countries with high level of intensification, or when small scale farmers have an unlimited access to pesticides. This suggests that we would probably have to widen our subject to the human factor. Farmers themselves have to be considered as a part of the “ecological attributes” of major cotton pests.

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HOST RESISTANCE TO THE LEAFHOPPER, AMRASCA DEVASTANS (DISTANT) IN COTTON, GOSSYPIUM SPP.

Abstract                                                                         Back to Table of contents

The cotton leafhopper, Amrasca (Empoasca) devastans (Distant) is a key pest on Upland cotton in India and an upsurge of the pest has been noticed in recent years.  The nymphs and adults desap the leaves resulting in hopperburn, drying and shedding of leaves, reduction in plant stand and loss in yield.  The management of this pest is made difficult by the development of resistance to insecticides and resurgence caused by indiscriminate applications of synthetic insecticides.  Among cultivated cottons, Gossypium arboreum and G. herbaceum are resistant to the leafhopper.  Resistance from these species were transferred to G. hirsutum cottons.  Among wild cottons, G. tomentosum, G. armourianum and G. raimondii are resistant to the leafhopper.

Morphology of cotton plays an important role in imparting resistance to leafhopper.  Hairiness of leaf, toughness of leaf veins, thickness of leaf lamina, length and angle of insertion of leaf hair are associated with resistance.  Non-preference for oviposition is because of high concentrations of allomones like tannins and free gossypol.  Non-reducing sugars, tannins, free gossypol and silica are key factors that influence the antixenosis mechanism.  Anti-nutritional factors like total phenols and epicuticular waxes exert significant adverse effects on leafhopper survival and oviposition.  In G. hirsutum, G. tomentosum and G. arboreum varieties, hairiness and leafhopper resistance are governed by a dominant gene.  The available resistance needs to be exploited both by conventional methods and new innovative techniques.  Cumulative resistance derived from diverse gene pools will be more lasting and there is need to identify new genes that govern the resistance.

Conclusions

For cotton farmers, use of leafhopper resistant varieties is economically cheap and reduces the need to use high cost inputs like insecticides. Given the problems associated with reliance on pesticides, the selection of insect resistant varieties is more pressing than ever before.  Even partial resistance may be useful as it may enhance the effect of natural enemies and possibly reduce the need for other control tactics.  Concerted efforts are essential to breed newer varieties as the present day cultivars are of narrow genetic base which would make them vulnerable to other pests and development of biotypes of leafhopper. Cumulative resistance, derived from diverse gene pools will be more lasting and research attempts should be directed in this line. For continued success of host resistance, research programmes should be directed to identify new gene(s) that impart resistance. Chemical ecology which encompasses the role of varieties that influence the host plant-insect interactions should be directed to identify the role of phytochemicals vis-a-vis host selection by leafhopper. Biotechnology, through the use of genetically engineered transgenic plants offers greatest scope and is one of the virgin areas of research with a lot of potential.

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