Gabriele Stoll
Natural Crop Protection in the Tropics
Letting Information Come to Life
Methods of Field Protection
Insect-controlling plants
It is assumed that a healthy soil and the various methods of cultural control, some of which are presented in the previous chapters, are the first steps in crop protection. However, in many cases, even when farmers apply sound cultivation practices, additional curative measures are needed to protect the crop to an acceptable level. Plants with pest-controlling properties may then be an option.
The use of plant extracts to control destructive insects or disease vectors is not new. Rotenone (Derris spp.), nicotine and pyrethrins have been used for a considerable time in small-scale subsistence and also commercial agriculture. Recently, considerable effort has been put into the development and promotion of plant-based methods and products for the control of pests. This has taken two different approaches.
 One has been a science-based approach that uses a formal set of steps to discover and determine efficacy, and attempts to either produce the botanical pesticide on a commercial scale or synthesize it for broader use in commercial agriculture (433).
 In parallel to the above approach there has been a considerable effort on the part of NGOs, action-oriented researchers and farmers to develop practical and low cost methods of botanical pest control. This has been most obvious for the use of neem, which has now reached large-scale use and acceptance. All other plants with pest-controlling properties play a rather local role. Bearing in mind the factors of importance for small farmers, plants for pest control should ideally possess the following characteristics.
They should:
• Be effective at a rate of max. 3–5% plant material based on dry weight
• Be easy to grow and require little space and time for cultivation or procurement
• Recover quickly after the material is harvested
• Be perennial
• Not become a weed or a host to plant pathogens or insect pests
• Possess complementary economic uses
• Pose no hazard to non-target organisms, wildlife, humans or the environment
• Be easy to harvest; preparation should be simple, not too time-consuming or require too high a technical input.
• Applications should not be phytotoxic or decrease the quality of a crop, e.g. taste or texture.

The following section combines information from the above two approaches but with a clear focus on usefulness to small farmers. The first part summarizes information in considerable detail on the most widely used plants. This includes information, where available, on undesirable side effects on humans (mammalian toxicity) and other environmental effects on beneficial insects and other important organisms. A less comprehensive overview follows under "Further plants with insect-controlling properties" and a second overview summarizing information on " Mixed preparations using plants with insect-controlling properties ".
All of this information should be viewed only as starting points. These need to be tested through plot and on-farm experiments for applicability to local conditions and adapted where necessary. Chapter 5 "Letting information come to life" has been included for exactly this reason. The contributors have been invited to share their experience and to provide suggestions on approaches and methodologies. It is hoped that this may encourage the user of this book to test the techniques proposed and others they know of for effectivity and applicability to local conditions, and to innovate and adapt them where necessary.

The printed version contains more information about the following plants:

Fish bean plant
Indian pivet tree
Malabar tree
Persian lilac (Paradise tree)
Pongam tree
Sweet flag