Botanical and biological features
The tomato (Lycopersicum esculentum Mill.) is a plant belonging to the Solanaceae family. It is an annual (under favorable conditions, perennial) herbaceous plant with an aggressive root system penetrating the soil to a depth of 1,5–2,5 m. Tomato is a very heat-loving crop. In most tomato varieties, seed sprouting begins at a temperature of 10–15˚С, but the optimum germination temperature is 22–25˚С. When the temperature drops down to 13–15˚С, the buds fail to open and ovaries fall off, the plant growth being arrested at 10˚С. Temperatures of 1–2˚С below zero are injurious for most tomato varieties, whereas light frosts (0,5–0,8˚С below zero) only damage flowers and fruit.
Tomato is resistant to air drought. This is due to its extensive and well-developed root system. For tomato plants to grow and develop normally, the soil humidity should be 70–80% of field moisture capacity, while the air humidity may be as low as 45–55%.
The highest yields are obtained when tomato is grown on light, structured, readily warmed up and humus-rich soils.
Tomato, as a light-demanding crop, grows well under conditions of long exposure to intense sunlight. In low light conditions, the plants take up atmospheric carbon dioxide slowly and plant growth and development is retarded. Tomato sprouts and seedlings/transplants are particularly light demanding.
The best preceding crops are winter cereals, annual legumes, cucumber, onion and early cabbage varieties.
The optimum sowing time for direct seeded tomato is when the soil at a depth of 5–6 cm has warmed up to 10–12˚С and its moisture content permits successful sowing. When grown by transplanting, tomato seedlings are planted out when there is no longer risk of spring frosts.
The plant density varies between 2 and 7 plants per 1 m2 (20,000–70,000 pl/ha) depending on plant vigor and growing conditions. The seeding rate is 0,2–0,3 g per 10 m2 (0,2–0,3 kg/ha) of open ground with transplanting, and 0,3–1,0 g per 10 m2 (0,3–1,2 kg/ha) with direct sowing.
In recent years, it has been common practice to grow tomatoes as a second double crop after early-harvested preceding crops (winter onion, early cabbage varieties, early potato, etc.). To this end, 35–45-day-old transplants of early tomato hybrids such as Debut F1, Sunshine F1 and Sunrise F1 are planted out in late June – early July. The tomatoes are harvested in mid/late September and sold at a premium price.
To obtain a tomato yield of 10–12 kg/m2, organic fertilizers should be applied at a rate of 40–50 kg per 10 m2 (40–50 ton/ha) and nitroammophoska at a rate of 700 g per 10 m2 (N 110, P2O5 110, K2O 110 kg of active substance per hectare). 70% of the total fertilizer applied is given with autumn plowing, and the balance plus 200 g of potassium nitrate and 100 g of ammonium nitrate per 10 m2 as supplementary fertilizing during the growing season. To improve the fruit quality (color, firmness, taste/flavor, and solids content), application of the bulk of the potassium nitrate is timed to coincide with the onset of fruit ripening. A characteristic feature of tomato is its very poor ability to take up phosphorus in early stages of growth. This is particularly the case at subnormal temperatures (lower than 12–13˚С). Therefore, preplant application of phosphorous fertilizers should be an obligatory cultural practice in tomato cultivation. The fertilizer application rates are adjusted according to the soil nutrient status data.
During the growing season, the tomato plants are given 5 to 10 irrigations with the water application rate of 350–400 l per 10 m2 (350–400 m3/ha). Combining drip irrigation with application of water-soluble fertilizers through the drip irrigation system (fertigation) is a highly efficient technique resulting in a more uniform moisture and fertilizer distribution in the root zone, more efficient water use, less soil compaction, and no soil crust formed. Readily soluble mineral fertilizers are given with each water application.
Major pests: the Colorado potato beetle, aphids, thrips, and cutworms. When growing tomatoes by transplanting, the roots of seedlings are, prior to transplanting, soaked in Actara suspension (1,5 g/l per 250 plants) for 90–120 min at 18–23˚С to protect the transplants against aphids, wireworms, false wireworms, and mole crickets. Later on, the tomato plants are sprayed, as necessary, with Actara and Karate Zeon to control the potato beetle. Actellic is used to control aphids and thrips. To control beet armyworm moth (Spodoptera exigua), cotton ballworm and tomato moth, the tomato plants are sprayed with insecticides such as Zolone, Match, Proteus and Shtefesin at the time of mass flight of moths, with sprays repeated every 10–12 days.
The most important tomato diseases: Late blight, Alternaria blight and Bacterial black spot of tomato. Sprays with fungicides such Acrobat, Ridomil Gold, Quadris, Cuproxat, Dithane M-45 and Tanos are made to control these diseases. To prevent the causative agents from developing resistance to fungicides, the chemicals used for sprays should be alternated.
In certain growing seasons, tomato crop is seriously damaged by stolbur (tomato big bud, or TBB) – a disease caused by phytoplasma. Main symptoms of TBB: lobes of young leaves become reduced in size, chlorotic, often with a shade of pink or purple. Sepals increase in size and fuse; inner flower parts are reduced – the pistil is shortened, the stamens are underdeveloped, and the petals are smaller in size, discolored or green. The fruit become lignified: the cross-section reveals white, strongly lignified vascular tissue. The control measures generally target principal phytoplasma transmitters (vectors) – leafhoppers. Eliminate weeds from the crop stand because these can act as reservoirs of infection and spray the tomato crop and adjacent fields and stretches of land with insecticides on a regular basis.