Tomatoes

Seedbed Preparation and sowing

Tomato growing starts from seedbeds, where seedlings are first raised before they are transplanted to the main fields. Seedbeds are prepared finely for ease of seeds germination. It is important

to choose a well drained area not recently cropped with solanacea crops.

A raised seedbed is formed 15-30 cm high with lower height in dry periods and being higher as it gets wetter. Seeds are sown in rows 6 cm apart. The bed is covered with a thin layer of compost and soil is not allowed to dry.

Raised beds are used to facilitate furrow irrigation and to improve drainage.

 

to choose a well drained area not recently cropped with solanacea crops.

Transplanting

Harden the seedlings by slightly reducing water and exposing them directly to sunlight 6-9 days before transplanting. Thoroughly water the seedlings about 12 hours before transplanting to the field. A good seedling is in the 4-5 leaf stage which is about 4 weeks old.

Transplanting is done in the late afternoon or on a cloudy day to minimize transplant shock. The seedling is inserted in a hole so the cotyledons appear above the surface. Tall, spindly seedlings should be buried deeper. Press soil firmly around the root, and water around the base of the plant to settle the soil. It is important to water the field as soon as possible after transplanting.

Plant spacing varies with cropping system either using single or double rows. Using two rows spacing is 60 cm between rows and 40 cm between plants. This gives a plant population of over 33,000 plants per hectare. Using single row and spacing of 40 cm between plant population is just over 16,000 on a hectare.

1. Water Use and Requirement

Insufficient water at any growth stage will reduce yield and fruit quality. Tomato is most sensitive to water deficit during flowering, somewhat sensitive immediately after transplanting and during fruit development, and least sensitive during vegetative growth.

However tomatoes do not like water logged conditions.

Any type of irrigation can be used spanning from surface, sprinkler, drip, water-tubing to just physical water fetching from the water source to pouring it on the plants in the garden. Either system will be used depending on individual farmer’s ability. Water conservation at the farm, will be through water catchment, rain water run-off, rain water harvesting, underground water pumping

2. Mulching

Mulching with appropriate material is used to cover the soil surface. Mulching is necessary for growing tomatoes because it reduces leaching of nutrients, conserves soil moisture and warmth as well as suppressing weeds.

  

3. Staking

Staking tomato plants with bamboo poles, wood stakes, or other sturdy material provides support and keeps the fruit and foliage off the ground. Staking can increase fruit yield and size, reduce fruit rot, and ease harvesting.

Indeterminate varieties should be staked to facilitate pruning, pinching, harvesting, and other cultural practices. Determinate varieties should be staked in the wet season to prevent fruit contact with the soil.

Many staking arrangements are possible. Plants should be fixed securely to the stake or string supports, beginning about two weeks after transplanting. Rice straw, plastic strips, horticultural fixing tape, or other materials can be used for fixing. Fixing should be done so fruit clusters are supported.

4. Pruning

Pruning or selective removal of side shoots to limit plant growth may cause fruit to mature earlier and grow to greater size and uniformity. Pruning improves air circulation within the canopy, which reduces foliar diseases, and facilitates spraying and harvesting.

Indeterminate varieties should always be pruned so they do not produce too much vegetative growth. The degree of pruning varies according to the season. Along with pruning is pinching which is the removal of unwanted flowers to control the number of fruits required.

5. Weeding

Weeds have to be removed from the tomato garden because they compete with the tomato vine for light, nutrients and water. They also host diseases and pests. The weeds are removed from the tomato garden by hand or hoe.

6. Soil Nutrients and Fertilizer Need

Tomatoes being greedy feeders will certainly need fertilizer application right from beginning to when they have started fruiting. Farm yard manure and compos are ideal for fertilizing a tomato plantation under organic production purposes.

Liquid organic fertilizers in form of the plant and compost teas will be necessary especially after fruit setting to stimulate more fruit formation.

As for non-organic production, several inorganic fertilizers will be added to boost the yields.

The main diseases affecting tomatoes are early blight, late blight, bacterial wilt and Fusarium wilt. The main pests of tomato are mites, whiteflies, leafminers  (Tuta absoluta) and thrips.

1. Bacterial wilt (Ralstonia solanacearum)

The disease causes rapid wilting and death of the entire plant without any yellowing or spotting of leaves. Total collapse of the plant usually occurring when temperatures reach 32°C and above. Plant wilts while still green. When the stem of a wilting plant is cut across, the pith has a darkened water-soaked appearance, and on squeezing the cut stem, a white, yellow or greyish, slimy exudate may appear. In later stages of the disease, decay of the pith may cause extensive hollowing of the stem.

Photo. Tomato plant infested by bacterial wilt

Management:

• If only a few wilted plants are found, immediately remove them from the field
• Practice long-term crop rotation (3-4 seasons).

2. Fusarium wilt (Fusarium oxysporum sp. Lycopersici)

The lower leaves of the plant usually turn yellow and die. One or more branches may exhibit such symptoms. Leaves on one side may be affected while those on the other side are symptomless. Diseased leaves readily break away from the stem. When affected stems just above ground level and petioles are cut diagonally, a reddish-brown discolouration of the water conducting tissues will be observed.

Photos: Symptoms of fusarium wilt on tomato

The fungus is both seed- and soil-borne. It causes most damage on light, sandy soils. It is most active at temperatures between 25 and 320 C. The fungus can survive in the soil indefinitely even when no tomatoes are grown. It can also survive in fibrous roots of weeds (e.g. Amaranthus, Digitaria and Malva species).

Management:

• Use resistant tomato varieties
• Use certified disease-free seeds
• Do not locate seedbeds on land where Fusarium wilt is known to have occurred
• Where soil is acidic, raise the pH by applying lime or farmyard manure
• Avoid excessive nitrogen fertilisation and control root-knot nematodes

3. Early blight (Alternaria solani)

Leaf spots of early blight are circular, up to 12 mm in diameter, brown, and often show a circular pattern, which distinguishes this disease from other leaf spots on tomato.

Photos: Symptoms of early blight on tomato

Management:

• Use resistant varieties
• Use certified disease-free seeds. If using own seeds, hot water treat the seeds.
• Use disease-free plants
• Practice roation with non-Solaneceous crops (e.g. eggplant, peppers, potatoes etc)
• Stake and prune indeterminate varieties
• If disease is endemic, applied preventative sprays of copper compounds (e.g. copper hydroxide)

4. Late blight (Phytophthora infestans)

Symptoms of late blight are irregular, greenish-black, water soaked patches, which appear on the leaves. The spots soon turn brown and many of the affected leaves wither, yet frequently remain attached to the stem.

Photo: Late blight symptoms on tomato plant and fruits

Management:

• Use resistant varieties
• Use disease-free transplants
• Stake and prune indeterminate varieties
• Practice crop rotation

5. Powdery mildew

Photo. Symptoms of powdery mildew on tomato

.6. Blossom end rot (Physiological disorder)

Photo: Stages of blossom end rot

It is caused by calcium deficiency and irregular watering. The disease occurs at the blossom-end of the fruit. It starts as a water-soaked spot that enlarges to become dark brown and sunken. The surface of the spot becomes dark and leathery. The rot is dry.

Management:

• Avoid water stress during early stages of fruit development
• Apply lime in calcium deficient soils
• Apply foliar sprays of 0.5% calcium chloride at fruit development stage.

7. Tomato viruses

Often spread in the plantation by insect vectors such as whitefly, thrips and aphids. The most important symptom of viral infections is the light (white or yellow) colour of the leaves, or a mosaic pattern of light and darker shades of green on the leaves. In many cases, viral disease leads to dwarfed growth, rosette formation or other strange stem and leaf deformations.

Viruses reported on tomato crop include:

• Tobacco mosaic virus or tomato mosaic virus (TMV or ToMV)
• Cucumber mosaic virus (CMV)
• Tobacco etch virus (TEV)
• Potato virus-Y (PVY)
• Potato leafroll virus (PLRV)
• Tomato spotted wilt virus (TSWV)
• Pepper veinal mottle virus (PVMV)
• Chilli veinal mottle virus (CVMV Or Chivmv)
• Tomato yellow leaf curl virus (TYLCV)
• Tomato Big-Bud mycoplasma (TBB)

Common control measures include:

•  Use tolerant varieties and certified disease-free seeds
• Protect seedlings with a net in the nursery.
• Control the insect vector.
• Eliminate weeds and ornamental plants that harbour the virus.
• Remove and destroy infected individual plants.
• Avoid an overlap of tomato crops
• Remove crop refuse and roots from fields
• Workers should not smoke or take snuff when working in tomato fields since the virus can be transmitted from tobacco.

7. Major Tomato Pests

The main insects of tomato are red spider mites and russet mites, fruitworms, whiteflies, leafminers and thrips.

7.1. Whiteflies

Whiteflies under leaf. Adult whiteflies are about 1mm long.

This whitefly is a serious pest of tomatoes. Whiteflies attack tomatoes from seedling to mature stage. They sucks sap from the leaves, and may weaken the plants. Feeding of whiteflies causes yellowing of infested leaves. However, the main damage caused by whiteflies is indirect as vectors of virus diseases. Bemisia tabaci transmits several virus diseases in tomato. In particular it is an efficient vector of the Tomato Yellow Leaf Curl Virus (TYLCV). Small numbers of whiteflies do not cause major direct plant damage. However, even small numbers of whiteflies may need to be controlled in areas where TYLCV is common.

Management:

• Time sowing and transplanting. If possible avoid the season when whiteflies are more likely to occur
• Check the crop regularly. Use yellow sticky traps to monitor the presence of whitefly adults.
• Remove weeds in advance of planting tomatoes, and keep tomato fields weed-free.
• If necessary spray neem extracts. Neem-based insecticides are reported to substantially reduce egg laying by B. tabaci, inhibit the growth and development of nymphs, and significantly reduce the risk of TYLCV transmission.
• Spraying with soap and water solutions reportedly controls whiteflies.
• Plant barrier crops.

7.2. Aphids (Aphis gossypii, Myzus persicae)

Photo. Green peach aphid (Myzus persicae)

Aphids such as cotton aphid (Aphis gossypii) and the green peach aphid (Myzus persicae) suck plant sap, which can reduce plant growth; they also secrete honeydew, on which sooty moulds growth. Sooty mould on fruits reduces their market value. These aphids may also transmit virus diseases during feeding such as the cucumber mosaic virus.

Management

• Conserve natural enemies. Aphids are usually kept under control by a wide range of natural enemies. In particular, avoid use of wide spectrum pesticides since they kill natural enemies
• Use reflective mulch. Reflective aluminium mulches deter aphids from landing on plants. The effect is lost once plants are large enough to cover the mulch

TUTA Absoluta

It’s a harmful mining moth with a strong preference for tomatoes and other crops in solanacea family.

symptoms:

TUTA Absoluta

Prefers leaves and stems. It also occurs underneath the crown of a fruit and sometimes inside.

Severe infection leads to drying of the leaves and sometimes dying of the whole crop.

Control:

Use of Chemicals; e.g. Emamectin benzoate and Abamectin alternatively for attacking both adult and larva.

Harvesting (Tomatoes)

Maturity period varies from 55 to 105 days. Harvest fruits that are fully ripened but still firm. Most varieties are dark red. Harvested tomatoes should be put under shade with temperatures less than 25^oC and a relative humidity of 80-90%. Light is not necessarily for ripening immature tomatoes. Some green tomatoes can be picked for a distant market.

Poor post-harvest handling can easily lead to poor quality tomatoes. Care should be taken not to injure the fruits or mixing them with damaged ones. It is advisable to harvest during cool temperatures such as morning or late afternoon.

Tomato yields vary from variety to variety and with system of cropping used and management.

Post Harvest management (Tomatoes)

Tomatoes will be ready for marketing immediately after harvesting. While tomatoes are classified as highly perishable vegetables, they take about three to four days kept at room temperature, and can take more than a week under refrigeration. They are also ready for factory processing after they have been cleaned. Tomatoes can be canned in a processing plant and will be stored for long period of time. Tomato paste is the product that will be produced from fresh tomatoes and can be stored for a long period of time in a can which is air tight. Canned tomatoes could have a varying time of shelf life depending on the intended use.