Introduction:

Tomato, scientifically known as Solanum lycopersicum, belongs to the family Solanaceae.

Today, a wide variety of tomato cultivars are grown worldwide, differing in color, shape, and size.

The length of the growth period for tomato plants depends on environmental conditions and temperature, the cultivar type, and the size of the plants. This growth period can range from 4 to 5 months. Tomato seeds are sown in a nursery or greenhouse, and once the seedlings reach the 2 to 4 leaf stage, they are transferred to the main field. In temperate regions, planting occurs after the risk of spring frost has passed, while in warmer regions, planting takes place in late winter. The plants are placed along furrows with a spacing of 50 centimeters and the width of the beds is 100 centimeters. The spacing between plants in the rows is 50 to 75 centimeters.

Soil and Fertilizer:

In cold regions, tomatoes are planted in sandy clay soils, while in warm regions, they are grown in clayey sandy soils. It is recommended to add 20-30 tons of well-decomposed manure, along with 50-75 kg of nitrogen and 100-150 kg of phosphorus and potassium fertilizers to the soil.

The optimal pH for the growth of this plant is between 5.5 and 7.

Required Temperature for Tomatoes:

One of the factors that inhibits proper pollination is high temperature. When daytime temperatures rise above 30 degrees Celsius and nighttime temperatures do not drop below 24 degrees, it adversely affects pollen development. When the temperature increases and heat stress occurs, irrigation should be applied to help the seedlings absorb more water, allowing them to adapt to environmental conditions. Once the weather cools down, irrigation should be discontinued.

Transferring Seedlings to the Field (Planting):

Before transferring seedlings, the soil must be prepared, and the soil should be worked to the desired depth based on the type of seedlings, making it suitable for planting by hand or with machinery. For planting seedlings in the main field, holes are created with a spacing of 40 to 60 centimeters. If the density of plants is considered to be 2.5 plants per square meter, approximately 25,000 plants are needed per hectare.

The best time to transfer seedlings to the main field is when the plant height reaches 20 to 30 centimeters. At this stage, two true leaves, in addition to the two cotyledons, will have developed, which typically takes 15 days for two leaves and 30 days for four leaves. The optimal time for transferring seedlings to the main field is 6 to 7 weeks after sowing seeds in the greenhouse. It is advisable to irrigate the greenhouse 12 to 14 hours before the transfer.

During the transfer, to help seedlings acclimatize to external temperatures, they should be kept outside the greenhouse for about 24 to 48 hours before being moved to the main field.

After transferring seedlings to the main field, they should be placed in a cool and shaded area. This is because seedlings in trays have limited space, and when placed outside the greenhouse, they experience higher surface evaporation, causing the seedling environment to dry out quickly, which can lead to seedling loss. Therefore, efforts should be made to minimize the time between transferring seedlings to the main field and planting them.

Transferring Seedlings to the Field (Planting):

Before transferring seedlings, the soil must be prepared, and the soil should be worked to the desired depth based on the type of seedlings, making it suitable for planting by hand or with machinery. For planting seedlings in the main field, holes are created with a spacing of 40 to 60 centimeters. If the density of plants is considered to be 2.5 plants per square meter, approximately 25,000 plants are needed per hectare.

The best time to transfer seedlings to the main field is when the plant height reaches 20 to 30 centimeters. At this stage, two true leaves, in addition to the two cotyledons, will have developed, which typically takes 15 days for two leaves and 30 days for four leaves. The optimal time for transferring seedlings to the main field is 6 to 7 weeks after sowing seeds in the greenhouse. It is advisable to irrigate the greenhouse 12 to 14 hours before the transfer.

During the transfer, to help seedlings acclimatize to external temperatures, they should be kept outside the greenhouse for about 24 to 48 hours before being moved to the main field.

After transferring seedlings to the main field, they should be placed in a cool and shaded area. This is because seedlings in trays have limited space, and when placed outside the greenhouse, they experience higher surface evaporation, causing the seedling environment to dry out quickly, which can lead to seedling loss. Therefore, efforts should be made to minimize the time between transferring seedlings to the main field and planting them.

Always consider about 10 to 15 percent more seedlings for the transplanting stage, as there is a possibility of losing some seedlings during the handling process. To minimize this loss, workers should exercise great care during planting to avoid damaging the roots and stems of the tomato plants.

Tomatoes are generally harvested between 70 to 100 days after transplanting, depending on the cultivar. The average duration from planting to harvest varies for different cultivars of large tomatoes, categorized as early, mid-season, and late varieties.

Weeds:

• Some of the weeds found in tomato fields include Gal Jaliz (Orobanche), foxtail, salsify, purslane, and mustard. The most significant current problem in vegetable farms is the presence of cancer, or the Gal Jaliz plant (Orobanche). This plant causes disruptions in plant growth, not only in Iran but also in many countries around the world.
• Gal Jaliz attaches its roots to the roots of the host crop and feeds on it, which can lead to the complete destruction of the host plant.

In this section, we discuss the problems, diseases, and pests affecting tomato fields

One of the most significant damaging factors for tomatoes is damping-off diseases, with key pathogens including Fusarium and Verticillium. In these diseases, the most common and critical damage during the early growth stages is crown rot, which ultimately leads to the collapse of the seedlings.

Another issue is the presence of viral diseases in the fields, the most common of which is the Tomato Mosaic Virus (TMV). This virus causes stunting, curling, distortion, and reduced growth of leaves, flowers, and the entire plant. The younger the infected plant, the more severe the damage it experiences.

The next disease is caused by the Tomato Yellow Leaf Curl Virus (TYLCV), which leads to leaf curling, reduced leaf size, and flower drop in tomato plants. This virus causes the most damage in tropical and subtropical regions. Viral diseases are transmitted by insects or wind, and one of the prevention strategies is to eliminate the insects responsible for spreading the virus.

One important point regarding viral diseases is that there is no definitive treatment for eliminating viral infections in the fields. To prevent the spread of the disease, it is essential to completely remove infected plants from the farm.

Another category of diseases affecting tomato fields involves fungi, with one of the most common being Septoria Leaf Spot, caused by the fungus Septoria lycopersici. Symptoms of this disease include round, water-soaked spots approximately 3 to 6 millimeters in diameter, featuring a gray center and a yellow halo. These symptoms are typically much smaller and darker on the stem, petiole, and calyx compared to the spots on the leaves.

Thrips, whiteflies, and miner flies are some of the most significant pests in tomato fields. The most destructive pest for tomatoes is the miner fly, which causes substantial damage to tomato farms in many regions, including Iran. The miner larvae affect various plant organs, potentially destroying 50% to 100% of the crop.

The most notable symptoms of this infestation are blister-like spots on the leaves. Inside these blisters, you can find larvae and black feces. Over time, the leaves become completely wilted, leading to deformation and total loss of the leaves.

Several factors can cause physiological abnormalities and reduce the quality and marketability of the product. Symptoms of physiological problems include leaf drop, fruit cracking, and blossom end rot. Blossom end rot, which occurs due to calcium deficiency in tomatoes, is one of the most significant and common factors affecting product quality. Other physiological issues can arise from excessive nitrogen use and irregular watering practices, leading to fruit cracking.

One prevention strategy for diseases and physiological problems is selecting resistant varieties suited to environmental conditions.

Damaged or diseased fruits that cannot be marketed should be removed from the plant but not mixed with healthy fruits. These damaged fruits must be collected from the field to prevent the accumulation of insects, pests, and the spread of diseases.

Tomato fruits should be harvested during the coolest hours of the day (early morning or evening). If harvesting is to be done in the morning, it is essential to wait until the moisture on the surface of the fruits has dried.