Crop production and crop protection

Diseases of Tropical Pasture Plants Ed. by J. M. Lenne and P. Trutmann. The first serious

Diseases

treatise

on its topic,

of Tropical Pasture Plants

edited by J. M. Lenne and P. Trutmann is a welcome addition to the library. When starting a tropical grass breeding project some years ago in Zimbabwe, I would have been grateful for such a handy reference. No doubt it will not be the last word on this increasingly researched and important subject. Presentation from the major perspectives of pasture species, disease organisms and regional experience helps to address readers of divergent interests, but perhaps is over fussy. For a text aimed at breeders, agronomists and presumably extension workers as well as pasture pathologists, a greater assistance to disease recognition could have been provided. Of the massive range of disease/pasture plant associations discussed, relatively few are presented pictorially. The photographs are of varied quality, generally too small and no indication of scale is given. No doubt the large positive balance of illustrations towards legumes reflects the relative economic importance of tropical legume diseases. This would not comfort grass agronomists or breeders needing to identify and assess the importance of diseases encountered in their trials or nurseries, or in the field. P. A. York

Diseases of Vegetable Crops Ed. by Denis Persley. ISBN 0 7242 53726. Aus $39.95. Queensland Department of Industries, Primary Publications, Australia, 1994. Information Series Q193024 This practical and user-friendly book is well presented and superbly cross referenced between 100 pages of text and 324 high quality colour photographs. A glossary of technical terms facilitates understanding and value to a wide readership, ranging from students to growers and specialists. Although produced with reference to crops in Queensland, it has much wider appeal since most of the crops and their diseases occur world wide. An early component of the book is a brief introduction to plant diseases

caused by fungi, bacteria and mycoplasmas, viruses and nematodes. Schematics illustrate life cycles and there is useful comment on host, pathogen and environment interactions and symptom expression. Eight major diseases common to many crops are detailed. The bulk of the text is devoted to the diseases of 18 important crops ranging from asparagus to tomatoes. For each crop, concise details of the cause, mode of infection, spread, importance, symptoms and management of each disease are presented with references to photographs. Chemical control methods are outlined but not specified, because recommendations vary between countries. This logical and simple format is backed by a good index of text and photographs. Limited additional reading, mostly originating from Australia and the USA, is recommended for those who require more information. E. C. Hislop

IACR- Long Ashton Research Station, University of Bristool, Long Ashton, Bristol, UK

Crop Production and Crop Protection by E-C. Oerke, H-W. Dehne, F. Schonbeck and A. Weber. ISBN 0 444 82095 7 Dfl. 290.00 (US$ 165.75.) Elsevier Science Publishers, Amsterdam. It is nearly 30 years since H. H. Cramer estimated crop losses on a global scale in his book Plant Protection and World Crop Production. Now an update of the losses is most welcome, especially as this study also provides information on the effectiveness of crop protection measures. In the introductory chapter. the prospect of a world population doubling to about 11.5 thousand million in the next 100 years is considered in relation to the level of nutrition required and potential to grow sufficient agricultural product. Most of this human population increase is occurring in the less developed countries, where food intake is already inadequate for large sections of their population. Clearly this has important implications for agricultural policy and is discussed in relation to factors such as plant breeding, fertilizer use and crop protection, concluding that it will not be

possible to feed people properly without effcctivc crop protection The development of crop protection, with emphasis on the different types of pesticides is outlined in a brief second chapter. The bulk of the book Chapter 3 which extends from pp. 72 to 741 sets out the authors cstimatcs for losses due to pathogens, animal pests and weeds. Problems of compiling the data and its analysis arc set out with certain definitions. such as yields without crop protection. actual yields using current practices and attainable yields, if present losses could bc avoided. The estimated losses arc then reported for eight crops: rice. wheat. barley, maize, potatoes, soybeans. cotton and coffee. For each crop thcrc is a thorough, critical well-illustrated analysis of the data. divided into each region and intensity of cultivation, and followed by an overall summary and extensive list of references. Referring to rice, it concludes that the attainable production has increased from just over 400 million tonnes in I965 according to Cramer to about 1000 million tonnes. However the losses arc still estimated at over 50% with present control measures. While losses due to Icafhoppers, planthoppers and the viruses they transmit has decreased. losses due to diseases and weeds remain high with changes in cultivation and extension of rice growing to less suitable locations. In each crop, attainable production, especially of the major cereals has increased over the last 30 years, but in the case of potatoes low production in many areas has counteracted increases in yields in Europe and North America. the percentage loss has Overall increased by up to nearly 10% compared to 1965 data dcspitc advances in crop protection techniques. except for coffee. where losses have been reduced by 4.7%. The final chapter puts the data in perspective and draws some interesting comparisons of crop losses in relation to pesticide use in different areas of the world. The modest yield increase of 39.6% due to crop protection measures is considered to be due mainly to the lack of adequate control in many regions. The authors conclude that for the foreseeable future agrochcmicals will continue to bc an indispensable weapon in the battle to protect crops. Therefore to harvest a higher proportion of the attainable yields will require

Crop Protection

1995 Volume

14 Number

8

689

Book reviews

increased efforts to develop crop protection measures acceptable to the masses of small-scale farmers, whose yields remain generally low. The data in this book is confined to a limited number of crops, but it will be an invaluable reference to all those involved in crop protection. Hopefully it will remind those who administer the R and D budgets that the pest war is far from over and much still needs to be done if we are to achieve the food production needed to feed the world in the next century. Initially the book may seem very expensive, but in terms of the time needed to collate such information, it should be regarded as a good investment. G. A. Matthews Principal Editor

Planthoppers: Management.

Their

Ecology

and

Ed. by R. F. Denno and T. J. Perfect. ISBN &412-02341-5 (hardback) (x + 799 pp; f65.00). Chapman & Hall, New York, 1994.

Planthoppers are those homopteran bugs that are classified into the 19 families that make up the somewhat obscure superfamily Fulgoroidea. The Delphacidae, with about 2000 species, is the best known of the fulgoroid families, principally because a few of its species are notorious pests of graminaceous crops, notably rice, sugarcane, corn, sorghum and cereals. Despite the obvious disincentives to the study of delphacids, with them being only 2-4 mm in length and having unremarkable features and cryptic habits, ‘. . . a small handful of renegade entomologists have studied delphacids in natural habitats . .’ and have made important contributions in evolution, behaviour and ecology. Editors Denno and Perfect have brought together the work of this disparate ‘group’ and have integrated it with the important but similarly scattered pest management literature on planthoppers. Information on applied aspects and their attendant ecological understanding has blossomed in Asia, ever since the agricultural changes introduced with the Green Revolution elevated the brown planthopper of rice from obscurity into one of the world’s most destructive crop pests. The book is thus aimed at both ‘pure’ and ‘applied’ ecologists and its intention is integration. Material is deployed in six sections intended to form a natural progression. ‘Host plant relationships’, with three chapters, comes first, then ‘Reproduction and speciation’ (three chapters), ‘Population ecology’ (three chapters), ‘Interspecific interactions and community ecology’ (four chapters) and ‘Ecological approaches to planthopper management’, with five chapters. The

690

closing section handles ‘Implementation of management options’ in two chapters. That such a vast and diverse amount of material has been brought together into a single large volume that has such uniformity of structure is a considerable editorial achievement, despite some overlap of content between chapters. But could the integrative function have been taken further for even more benefit? An indication that such might be the case derives from the not surprising observation that different authors approached their tasks with different goals. Such differences probably reflect different views of method in science. Several chapters are essentially encyclopaedic, including some of those that deal with patterns of host relationships, life history variations and the various ecological interactions that involve planthoppers. Consequently, the tome includes a wealth of bibliographic material, which covers 89 pages (or 11% of the whole), as well as a great deal of extracted information presented in structured form in tables and appendices (185 pages, or 23% of the book). Some of these compilations are extensive, with three of them (on host plant and parasitoid records) together making up almost 60% of the tabular content. On the other hand, certain chapters are almost entirely synthetic, most notably those that deal with pesticide use and extension programs in relation to planthopper ecology in south-east Asian rice production. Here the emphasis is on the identification of major problem areas that require innovative conceptual development, as well as on planning research according to any such developments. Unfortunately, too few chapters lean towards this end of the ‘epistemological spectrum’. That material in some of the chapters has consequently been inadequately treated is illustrated by the approach in some of the ecology and biological control chapters. Although authors have acknowledged deficiencies in several core areas of current theory, none has capitalised fully on the realisation. In other words the tendency here has been to catalogue, when the material calls rather for a more conceptual and analytical treatment. It seems to be far too easy and too acceptable for ecologists to suggest repeatedly the ‘need’ to collect yet more data of a type given significance only by theories already deemed, by the same author, to be deficient. In the planthopper book this occurs when density relationships such as numerical responses and interspecific competitive interactions are discussed. Could such suggestions not stand in the way of sorely needed developments in the science? Another pitfall inherent in the encyclopaedic approach is that anecdotal observational evidence is often accepted

Crop Protection 1995 Volume 14 Number 8

unquestioningly. Such glib acceptance when interpreting population trends in biocontrol situations, for example, contrasts quite strongly with the lack of consensus about these points in the moresyntheticoftheecologicalchapters. Therefore, the way in which authors actually deal with information needs serious attention when compilations centred on a taxonomic group are developed. However, both general approaches to summarising information undoubtedly have their place and inherent interest, and care can be taken to safeguard high quality information from contamination with unsubstantiated information, as has been done with some of the host record compilations that appear early in the book. Nevertheless, introspection on the part of editors and publishers who may be contemplating equivalent volumes on other taxonomic groupingswould not go amiss. Perhaps one could start by contemplating what a shelf lined with a diversity of such broadly defined volumes of this nature might inspire? The outcome of any musings suggested bythecommentsaboveshould,however, be balanced by the planthopper book nevertheless being an engaging one. The compilations deal largely with the life of organisms that are, at best, probably only poorly known to most. That the unknown is still vast and holds excitement and interest comes across strongly in the early chapters, and is refreshing in an age that encourages the universal and invariably unimaginative search for economic justification. The analyses bring out some interesting phenomena. For example (i) the planthoppers are mostly grass feeders, but those that have adapted to island conditions have mostly moved onto dicotyledons, (ii) adults feed on the above ground parts of plants whereas the nymphsaremostlysubterraneanfeeders, (iii) the proportion of delphacid species with wing dimorphism is unusually great, including for example 89% of 75 Fennoscandian species in 39 genera, (iv) the males of all species are fully winged, presumably because it is always the males that travel around to seek out mates that may be situated at a distance, whether in temporary habitats (where females tend to be winged) or in more permanent ones (where females tend towards aptery), and (v) the structure of sexual calls is similar among the morphs within a species, which illustrates the pre-eminence of accuracy in sexual communication within a species gene pool. A considerable amount of evolutionary interpretation helps with cohesion. Furthermore, the book necessarily deals frequently with a geographical area that is not commonly cited when scientific examples are reviewed. The conceptual developments in pest management that have originated in south-east Asia, and