Application of Pesticides to Crops

The following sections are included:

• CONTENTS

• PREFACE

• ACKNOWLEDGEMENTS

Most pesticides are applied as liquid sprays formulated for dilution in water and are applied under pressure through hydraulic nozzles. In some situations an adjuvant may be mixed with the spray to improve rainfastness, reduce evaporation or increase uptake by plants. There is still a need for some specialised formulations with a petrochemical or vegetable oil diluent, that are applied undiluted as ultra-low volume sprays, and others are used dry as granule or dust treatments. This chapter provides a general outline of the different types of nozzles and the portable, tractor-drawn and aerial equipment used on the range of crops described in subsequent chapters. Irrespective of the formulation used for spraying pesticides, the most important part of the equipment is the nozzle as this is where the atomisation into spray droplets occurs. Metering the volume applied is also often a function of the nozzle, although on some equipment there is a restrictor associated with the atomiser. In this book, therefore, much emphasis is given to the correct selection and operating conditions for nozzles used to apply the different types of pesticides.

The “green revolution” has led to significantly increased yields of the major cereal crops over the last four to five decades following the efforts of the Consultative Group of International Agricultural Research (CGIAR) with emphasis on plant breeding and conservation of genetic resources. Increased yields have required greater use of fertilizers and pesticides, without which a far greater area of land would have been needed to maintain adequate stocks of grain. The demand now is for more sustainable agriculture, yet if the increasing world population is to be fed, high yields will continue to be needed and losses due to insect pests, pathogens and weeds must be minimised. Estimates of yield losses are given by Oerke et al. (1994). Orson (1997) reviewing pesticide management in the UK wheat production sees future optimisation as minimising environmental impact while achieving acceptable financial margins. This will require complex decision making to attain sustainability by encouraging biodiversity, particularly on noncropped land and cropped field margins, avoiding pesticide resistance and maintaining soil health…

Rice (Oryza sativa) production systems differ significantly in different parts of the world. Most rice is irrigated although in some areas upland rice may be grown in areas of high rainfall. In the flood deltas in Asia, rice is grown at sea level, but in the Himalayas some rice is grown at 3000-m altitude. In the USA, rice may be sown with pre-germinated seed dropped into standing water and subsequently treated with fertiliser and pesticides by aircraft in contrast to the manual treatments on small farms in Asia, where traditionally young plants were raised in seedbeds and transplanted when 15–25 cm high into rows 15–30 cm apart. This method of transplanting and flooding fields provided excellent cultural weed management. However, with movement of labour to urban areas and the costs of transplanting increasing, more farmers are now broadcasting seeds directly into the rice paddies (Heinrichs et al., 1987). This has increased the problems of weed management and led to an increased use of herbicides to combat yield losses that may reach 50%. Pesticide inputs are highest in Japan, where most rice growers have other full-time employment…

The following sections are included:

• Maize

• Weed management

• Insect pest management

• Disease control

• Sorghum and Millets

• Bird control

• References

The following sections are included:

• Cotton

• Herbicide application

• Insecticide application
  • Hydraulic sprayers
  • Air-assist sprayers
  • ULV/CDA
  • Electrostatic sprays
  • VLV/CDA
  • Aerial
  • Fungicide application

• Defoliant application

• Other Row Crops

• References

Tree crops have always needed special equipment due to the geometry of the different crops. This chapter considers apples, hops and vineyards. Tropical tree crops are discussed in the following chapter.

A number of tree and bush crops, especially those grown on plantations have been treated with pesticides to avoid major crop losses. In the absence of fungicides, coffee was abandoned in Sri Lanka in the 19th Century due to devastating infestations of leaf rust (Hemileia vastatrix) and replaced by tea, although in South East Asia cultivars of coffee resistant to the rust are now grown. Weed management has been using postemergence herbicides to maintain pathways for harvesting, especially in oil palm and rubber estates. Apart from spraying coffee for leaf rust control, other examples of fungicide spraying include bananas for Sigatoka disease (Mycosphaerella musicola) control, cocoa for black pod (Phytophthora palmivora) and rubber to control the South American leaf blight (Microcylus ulei). Biological control of insect pests is more important on perennial crops and natural enemies need to be conserved, so selection and use of insecticides needs to be very judicious. Unfortunately, some insecticides have been used with disastrous results by exacerbating other insect pest problems, for example insecticides applied to citrus, mangoes, olives and other crops often increase the damage due to scale insects. The investment in crop protection is often a fixed cost, but as the income may fluctuate due to the yields attained and world prices, the proportional cost of using pesticides can vary, so every effort is needed to optimise their use and minimise costs…

The demand in many countries for certain crops to be available throughout the year has led to an increase in cultivation under glass or plastic in order to extend the growing season. In the Mediterranean area alone, 400 000 ha were under plastic (Castilla and Hernandez, 1995 ) and this area is expanding. Protected cropping has also extended to tropical countries where irrigation is used throughout the dry season. Apart from the export of flowers, notably roses and chrysanthemums and of potted plants such as poinsettias, the cultivation of vegetables such as tomatoes, cucumbers and green peppers under plastic has increased. Growing these crops under glass or plastic increases temperatures, while irrigation raises humidity and extends periods of leaf wetness, thus providing a more favourable environment for pests and diseases. However, consumers demand clean produce, which has led to zero tolerance of damage. Growers’ response to this has led to the over-use of pesticides. Many pests have now become resistant as growers have sometimes sprayed twice a week over extended periods. With continuous cropping of some vegetables, particular care is also needed to ensure that the minimum interval between treatment and harvesting specified on the label of pesticide products is maintained…

Consumers would like to have organically grown vegetables, but with continuous cropping of many types of vegetables crops so that supplies can be maintained to markets over long periods, the incidence of pests and diseases will inevitably increase and cause some damage. Some of this damage may be relatively minor, but will affect the cosmetic appearance of the produce being marketed. Some vegetables are grown on a large field scale, while others are grown close together in relatively small areas, but in each case growers often have difficulty in rotating crops sufficiently to minimise soil pests, such as nematodes. These problems make it difficult to develop pest management programmes without the use of some pesticides. Thus, as with other crops, the aim is to select as far as possible cultivars resistant to pests and diseases and to minimise the need for pesticide treatment by careful regular crop monitoring, and use of weather forecasting and prediction models…

The treatment of turf on sports fields, golf courses and in other amenity areas provides a relatively simple target compared with the complex foliage of crop canopies. However, in generally open situations the wind could affect sprays where spray drift must be avoided due to the close proximity of sites accessible to the public. The situation is accentuated when weeds are chemically controlled on pavements and fencelines around buildings. Equipment developed for agricultural purposes has therefore been modified by those responsible for treating turf and pavements.

Most of the methods of application described in the preceding chapters illustrate the present state of the art in terms of adoption by farmers in different parts of the world. The latest technology aimed at optimising dosage transfer with minimal environmental pollution is not always used by growers who continue to use old equipment or are unaware of alternative methods. Everywhere people are increasing their opposition to the use of pesticides, yet they still require good-quality produce at low cost. Scientists, in response to the initial criticism of pesticides by Carson (1962), have developed the concept of integrated pest management with greater emphasis on natural controls, namely cultural and biological. As indicated in the Preface, much attention is now being given to development of genetically engineered crops with increased resistance to pests — development which is also attracting vocal opposition from the public as they perceive adverse effects from long-term exposure to small amounts of toxic chemicals in food crops. Genetically engineered crops so far have resistance usually only to one type of pest and other pests can still affect yields and crop quality. Crop cultivars, whether naturally selected or genetically engineered, that are resistant to pests often contain higher quantities of some substances which are toxic, thus, some lettuces resistant to aphids have a bitter taste and some varieties of potatoes were withdrawn due to unacceptable levels of solanin…

The following sections are included:

• APPENDIX 1

• APPENDIX 2

• APPENDIX 3

• APPENDIX 4

• INDEX