Flourishing botanicals sector for Tanzania

Tanzanian farmers still rely on synthetic pesticides despite their expense and environmental and health hazards. Development of IPM strategies could include low cost, less hazardous methods of botanical origin. Maulid Walad Mwatawala reviews the potential for effective use of botanical preparations in Tanzania.

Tanzania’s economy is largely dependent on agriculture, with 80% of agricultural output produced by smallholder farmers1. For many years, producers have relied on the use of pesticides and pesticide imports increased 26% between 2000 and 2003, according to FAO figures. However, chemical control is often beyond the pocket of low income farmers. Development of pest resistance to pesticides, consumer concern about residues in food and the effects of pesticides on the environment have also triggered a search for alternative cultural, physical and biological methods2. These alternative control methods have not been found effective in controlling pests when applied singly, except in a few cases. It is therefore desirable to use the various control techniques in combination while advocating minimal use of pesticides, hence the concept of Integrated Pest Management (IPM).

Pros and cons of botanicals

Environmental friendliness
Widespread pesticide application in agriculture and public health has resulted in their accumulation in the environment. This is compounded by negligence and ignorance, as exemplified by the gross contamination at Vikuge farm in Tanzania4 (see p12-14). Many plant-derived preparations comprise an array of plant chemicals, which act on both behavioural and physiological processes. Some may possess insecticidal properties, while others repel pests or discourage feeding or egg-laying activity. For example, seeds and leaves of the neem tree Azadirachta indica work as both anti-feedant and growth regulator. Many botanical preparations used for pest control are broad spectrum, with a short period of activity, often deactivated quickly by sunlight. As such, they are readily biodegradable, so they are usually less harmful to the environment and less likely to persist as residues in food. Also the waste from the botanical extraction process can potentially be used as a natural fertilizer5.

Suitability for small-scale farmers
With chemical pest control costs skyrocketing, many Tanzanian farmers can no longer afford to buy pesticides. Reducing production costs is key to any successful IPM programme. Many indigenous botanical preparations used to control pests can be made from locally available plants and entail little or no cash cost in using them6. There is still considerable knowledge in rural communities of how they can be used and farmers can easily start to use them.

Less likelihood of resistance
Resistance to pesticides develops as resistant individuals in a pest population survive a dose of pesticide lethal to normal pests and then reproduce. Cases of resistance to insecticides are becoming common and the consequences include more frequent application of pesticides, higher doses and more environmental contamination. Many synthetic insecticides rely on a single active ingredient, and once a population becomes resistant to it, the pesticide become useless. In contrast, botanical preparations contain a highly variable mixture of different plant chemicals, reducing the chances of provoking pest resistance.

Possible disadvantages 
Presence of pesticide residues in foods, feeds and ecosystems causes widespread concern. There is a need to develop products that will leave less harmful or zero residues and many botanicals can meet this requirement. However, certain plant species exhibit acute mammalian toxicity, for example, nicotine from tobacco plant extract is classified as WHO Class Ib ‘highly hazardous’ and rotenone from Derris and Tephrosia species is Class II. Rotenone and natural pyrethrum from chrysanthemum are highly toxic to fish and can harm aquatic organisms. For these reasons, pure nicotine is prohibited in IFOAM organic farming standards7.Botanicals may sometimes have lower efficacy than synthetic pesticides, they can be time consuming to prepare and may smell unpleasant. Furthermore, local knowledge of their location, identification and preparation is disappearing and farmers may be reluctant to use them as they are often derided in comparison with modern agricultural practices. 

Botanicals in Tanzanian IPM 
Various crop-specific strategies have been developed by the Tanzania-German project for IPM, in collaboration with various research institutions. These include methods for cotton, coffee, maize in field and in storage, brassica crops and tomato8. Table 1 summarises botanical, cultural, physical and biological methods designed for cabbage and other brassica crops. Neem is specifically recommended for diamondback moth caterpillar in brassicas. For pests of coffee, botanicals like tobacco, neem and Derris have been recommended for controlling various insects, including Antestia bug, green scales and white coffee borer. 
    These examples show there is great potential for using botanicals in Tanzania. However, there are major constraints on implementation of IPM, which could indirectly affect the uptake of botanicals, including: 

• lack of awareness of policy and research findings at farmer level
• lack of awareness of pesticides hazards by the public
• insufficient enforcement of pesticide legislationl lack of professional recognition for on-farm IPM research and training
• insufficient knowledge and exchange of information at all levels