Charles Kimani
In most Kenyan homes, a meal is not complete without tomatoes making tomato growing an attractive venture for most farmers in agribusiness. However, tomato growing has its fair share of challenges especially since tomatoes are highly suspecitible to pests and diseases. Farmers need to be adequately informed as lack of information can leave the farmer using synthetic pesticides indiscriminately and this has adverse effects on human beings and the environment.
David Too an avid listener of Kilimo Hai, a radio program aired every Thursday at 7.30pm on Radio Maisha recently called in to inquire how he can grow tomatoes organically, after realizing that dependence on pesticides is not only expensive but also hazardous to human health.
Common pest management
The common tomato pests in the East African region are red spider mites, russet mites, fruit worms, whiteflies, leaf miners and thrips. In Organic farming, adopting preventive measures and good farming habits is key if one is to realize better yields. The following are effective cultural control of the pests:
- Early elimination of weeds at least 2 weeks before transplanting
- Use of biopesticides such as pepper to control pests and viruses
- Plough and harrow the field before transplanting. This will expose cutworms to natural enemies
- Plant repellant plants such as chia seed, marigold and chives around the plantation
- Conserve natural enemies such as ants that help in controlling cutworms
- Dig near damaged seedlings, this destroys cutworms
- Make barriers to protect the transplanted seedlings. Barriers can be made by wrapping paper, aluminium foil, thin cardboard or similar materials around the base of plant stems. Toilet rolls are handy as cutworm collars since they are readily available and are bio degraderble.
Controlling Tomato Diseases
There are three main diseases that affect tomatoes: blight, bacterial wilt and black-end rot.
- Tomato Blight
Tomato blight is one of the most devastating disease in tomato production. A major symptom of the disease is dry brown lesions on stems, leaves and fruits. Affected fruits appear rotten and fall prematurely. Tomatoes are most susceptible to blight during cold and wet weather. This is due to high levels of moisture on the leaves for a prolonged period, which is a conducive environment for the fungal spores to germinate and spread rapidly. Preventive spraying using organic fungicides is the best control measure but once the disease has set in, there is nothing much a farmer can do. The loss incurred could be 100 percent.
b) Bacterial Wilt
This disease is caused by bacteria. Tomato plants attacked by bacteria wilt wither and then dry up even when the weather condition is wet. In organic farming, certified seeds and crop rotation are used to control the disease.
Culturally, these diseases are controlled using the following approaches:
1. Use of certified seeds and avoiding establishing of the seedbed on the fields that are infected.
2. Encourage crop rotation, pruning and staking for air circulation to reduce humidity as humid conditions are favourable for late blight.
3. Avoid overhead irrigation and provide space between crops as required.
4. Plant more resistant tomato varieties.
- Blossom-end rot
The disease is manifested on the fruits where the blossom ends appear rotten, and water soaked or rotten and dry. Blossom end rot is not caused by any organism. It is a physiological disease caused by:
- Too much nitrogen in the early stages of growth
- Irregular or infrequent watering
- Calcium deficiency in young fruits.
The disease can be controlled through:
- Regular watering
- Top dressing the crop with the right amount of nitrogen
- Application of calcium compounds in the soil.