Feedback: All you wanted to know on tomatoes grown in the field

A-Z OF GROWING TOMATOES IN FIELD

Please educate me on how to grow hybrid tomatoes on one acre, from seedlings to maturity.

Washington, Bondo

Production: Hybrid is very costly and needs care in handling for maximum profit. Ana F1, Prostar and other kinds of seeds can be found in your local market as advised by the stockist.

Transplanting: The best way is to start from the nursery by raising seedlings (transplants). This will take 28 days to have quality seedlings for the field.

Seed rate and economic returns: Tomatoes need 200-500g/ha depending on spacing. On cost, it depends on the type of hybrid you go for.

In the market, Maxim F1 hybrid is available at 2,000 seeds at Sh2,000. From my recent trial, I was able to realise 19.2 tonnes/ha in a greenhouse, which translates in field production to 13.6 tonnes/ha due to environmental factors that may reduce the profit margin.

If you sell tomatoes at Sh80 per kilo, then possibly your gross margin will be Sh1.09 million. Production expense cost of Sh125,000 will give a net of Sh963,000.

Field production: Plants depend on the soil for physical support and anchorage, nutrients and water.

The degree to which the soil adequately provides these three factors depends on topography, type, structure and management.
For tomato production, proper tillage is crucial for adequate soil management and optimal yields. Land preparation should involve enough tillage operations to make the soil suitable for transplant establishment and to provide the best structure for root growth and development.

The extent to which the root systems of tomato plants develop is influenced by the soil profile. Root growth will be restricted if there is a hard pan, compacted layer or heavy clay zone.

Agronomy: Agronomic practices include nutrient management, irrigation, support, pruning, weeding, pest and disease management, harvesting and marketing.

i) Nutrient management: Tomato is a heavy feeder and a heavy yielder if attended well. Crop nutrient requirements change with each stage of growth.

The general principle is to apply phosphate fertiliser as basal dressing for root development. For this, DAP or TSP can be used at the rate of 150kg/ha.

After transplanting, either urea or CAN can be used for leaf establishment. Apply urea after 2-3 weeks or CAN in the fifth week. Both are applied at the rate of 200kg/ha.

At the onset of flowering, top dress with NPK at 200kg/ha. A compound fertiliser is necessary for the supply of N, P and especially K that is needed for flowering.

The NPK top dress can be repeated after the first harvest. To correct micro-nutrient deficiencies, foliar feeds can be applied alongside the regular pesticide applications.

Inadequate calcium can lead to blossom end rot disease, which can be corrected by applying calcium fertilisers.

(ii) Irrigation: The amount and frequency of irrigation depends on prevailing weather conditions and the stage of growth.

Avoid irrigation in the evening to prevent disease development. Apply water regularly during dry spells to reduce physiological problems.

Irrigation should also be done after each harvest. Avoid excessive watering as this may lead to leaching of nutrients and waterlogging.

(iii) Support: Plant support is done by trellising the tomato on poles and wires. This is usually done early at three weeks after transplanting to avoid plant damage. This depends on the hybrid variety.

(iv) Pruning: Remove side shoots, laterals, old leaves, diseased leaves and branches and overshadowed lower leaves by hand, which turn to sinks of photosynthesis.

After formation of the first fruit cluster of mature green tomatoes, remove all the lower older leaves to allow for ventilation and disperse food to the fruits (defoliation).

Flowers should be pruned to 5-6 per cluster for medium-large sized fruits.

(v) Weed management: The crop stand should be kept free of weeds at all time, because weeds compete for nutrients and are also vectors for disease.

Hand weeding is recommended both for the greenhouse and outdoor tomatoes.

(vi) Pests and diseases: Always scout for pests and diseases in the morning because this is the best time to get all the pests on the plant.

Common pests include aphids, thrips, whiteflies, cutworms, bollworms, leaf miners, spider mites and nematodes. Common diseases include wilts, blight, leaf spots and mildews.

Tomato diseases
Late blight: The disease, which was responsible for the Irish potato famine in the mid-nineteenth century, is caused by the fungus-like oomycete pathogen Phytophthora infestans.

It can infect and destroy the leaves, stems, fruits, and tubers of both potato and tomato plants.

Bacterial wilt: The disease is very common particularly during the rainy season but also when there is excess moisture or humidity in the greenhouse.

This disease can spread very fast wiping away plants within a short time. The disease also affects fruits.

Symptoms:Dropping of leaves. The disease leads to rapid death of the entire plant. Management: Crop rotation, management of nitrogen and field hygiene.

Fusarium wilt: Soil-borne fungus that infects tomatoes at any age. The wilt organisms usually enter the plant through young roots and then grow into and up the water conducting vessels of the roots and stem.

Infected leaves later show downward curling, followed by browning and drying.

Management: Seek advice from nearby agrovet.

Early blight: Disease development is most serious during warm wet conditions. Tomatoes infected with early blight develop small dark brown to black spots on lower shaded leaves, stems and fruits.

In older crops, stem death occurs while leaves fall off the crop and fruits drop prematurely.

Management: You can seek help from nearest agrovet. Carry infected part of the plant, may be a leaf, to the agrovet.

-Peter Caleb,
Department of Crops, Horticulture, and Soils, Egerton University.