Analysis: FRANCIS MAKASA
TOMATO prefers relatively warm daytime temperatures of between 10oC to 30oC. Too high temperatures may reduce fruit production while frost in winter, may damage the crop. Crop rotation with non-solanaceous plants and other good cultural practices are critical in disease and pest control.
Farmers need to deal with several challenges to successfully grow tomatoes.
FRUITS VERSUS LEAVES
The farmer desires to maximise fruit production as opposed to leaves. For maximum yields, the plant must ideally start to bear fruits as low as possible on the stem. Hence it is desirable to transplant the seedlings as young as possible. Delays in transplanting will make plants concentrate on leaf growth in order to fight off competition for light from other plants and may delay initiation of flower buds.
It is important to stake the plants early to enhance air circulation and expose the plant to adequate sunlight. To avoid injuring roots, stakes should be placed at designated planting stations before seedlings are transplanted. Pruning of excess branches must be on-going as the plant grows. Avoid application of nitrogen rich fertiliser or poultry manure late in the plant’s life as it promotes leaf growth and delays fruit setting.
When grown during the rainy season, tomato is affected by fungal diseases that attack leaves such as early and late blights and powdery mildew. The farmer should spray suitable fungicides to the crop at least once per week to control fungal infections. Wherever possible, the farmer should vary the fungicide to avoid resistance.
TUTA ABSOLUTA PEST
Tuta absoluta may completely destroy the crop. The greenish larva of Tuta absoluta burrows both in the leaves and the fruit of tomato creating tunnels and extensively damaging the tomato plant including the fruit as it feeds on the plant tissue. The pest delays the larval stage as long as the food source is available.
Because it is found inside the plant, the pest is extremely difficult to control with pesticides and also develops resistance against pesticides. Several pesticides can be used in combination with cultural control measures. Control measures recommended include; clearing all crop residues on the soil, eliminating all the crop remnants immediately after harvesting the last fruit and selective elimination of affected plants. Crop rotation with non-solanaceous plants, timely weed control and proper fertilisation and irrigation are all good control measures. Farmers should avoid buying foreign seeds that are not certified in Zambia.
Spider mites suck the cell content of leaves thereby depleting the chlorophyll (the green material that produces plant food) in the cells. As a result of mite infestation, leaves may then turn yellowish or reddish and then detach completely from the plant. Webbing may extensively appear on the surface of the affected leaves, twigs and fruits. Damage is more severe in water stressed plants. Affected plants are stunted with reduced yields.
The tiny pests live in colonies of hundreds mostly on the underside of leaves and look like minute white or red dots moving about. They reproduce quickly in hot weather and are therefore common from August to November in Zambia. To detect mites, one can shake a few off the suspected leaf surface onto a white sheet of paper. Once they are disturbed, they move around rapidly.
Many natural enemies like thrips, lady beetles, certain flies and predatory mites control spider mites naturally. Hence one should avoid spraying broad-spectrum insecticides to avoid killing these desirable natural enemies and cause frequent mite outbreaks.
Water under pressure from a hosepipe washes away the mites physically. Spraying plants with insecticidal oils or soaps such as potassium soap is helpful. Adequate irrigation is important since water stressed plants are the most vulnerable. Because dusty conditions often lead to mite outbreaks, it is important to apply water to paths in and outside the garden on a regular basis.
In order to successfully grow tomato throughout the year, the farmer must be poised to deal with several pertinent challenges.
The author is an agricultural and rural development specialist.