Introduction

From an ecological perspective all organisms are part of nature, irrespective of what they do. To a farmer, all organisms that reduce the yields of their crops are considered pests, diseases or weeds. Insects, birds or other animals are also pests whenever they cause damage to crops or stored produce. Fungi, bacteria and viruses are also recognized as disease causing organisms when they lead to conditions that interrupt or modify the vital functions of growing plants or stored produce. All unwanted plants that grow within crops and compete with them for nutrients, water and sunlight are considered weeds. Such plants can also be hosts for pests and diseases.

Presence of these organisms in crop fields is not a problem until their numbers increase beyond a level where they attack, and cause substantial reduction in field crop yields or quality of harvested and stored produce. Farmers, who wait until this moment, often depend on aggressive and very harmful methods to limit damage. However, since many African small-holder farmers neither have the access nor can afford such methods and products, yield and quality losses are often substantial. In general, challenges associated with pest, disease and weed management can be summarized as follows:

• Wide diversity of pests, diseases and weeds - In sub-Saharan Africa a wide variety of pests, diseases and weeds occur because of the favourable, humid conditions nearly throughout the year. Because of this, many new pests, diseases and weeds evolve or are introduced, mostly accidentally, in the region. It, therefore, proves very challenging for farmers to recognize, distinguish and control the different pests, diseases and weeds.
• Poor monitoring - Many farmers lack knowledge on the cycles of specific pests, diseases and weeds and find it difficult to distinguish their specific characteristics. As a result, they cannot apply suitable preventive measures nor implement proper control measures.
• Limited access to pesticides - The great majority of African farmers lack the financial resources to buy chemical pesticides to control pests, diseases and weeds.
• Limited knowledge on suitable pesticides - There is a wide variety of pesticides available on the market, including ineffective ones. Since the majority of farmers cannot read and interpret the contents, prescriptions and other precautions, they cannot make proper choices on the best pesticides. They instead rely on recommendations from the pesticide retailers, who often lack the proper knowledge themselves and are often more motivated to make sales than advise farmers.
• Lack of knowledge on proper storage and application of pesticides - Farmers are exposed to high health risks in the case of improper application of pesticides; for example, the majority lack appropriate protective gear. In addition, synthetic pesticides and application equipment are usually stored inside homes, where food and children are exposed to them. Also, treated crops are sometimes harvested without proper observation of pre-harvest intervals, thereby exposing consumers to greater health risks.

This is a clear indication that the management of pests, diseases and weeds is still very challenging to many farmers all over Africa. To avoid major crop losses, the farmers should be able to implement affordable and effective measures which should not substantially increase their production costs or harm beneficial organisms in the ecosystem.

Generally appropriate methods and products should be:

• Easy to apply at minimal extra cost.
• Applicable in the local situation and conditions.
• Safe to handle, with minimal or no residual effect.