Successful tomato production dependent on holistic approach

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Successful tomato production is determined by a multitude of interactive elements such as variety choice, environmental conditions, the weather, soil health, and management practices. Understanding how each of these interact with the others is the key to unlock the potential good yields, delivering a high-quality product, and optimising profit.

“A holistic approach is needed,” emphasises Werner Wessels, area sales manager at SADC South Countries, Syngenta Vegetable Seeds.

“Balancing environmental conditions, plant physiology, water management, and soil health is important. When farmers understand this, they can make informed decisions and optimise their production for long-term success,” he says.

According to Jandri Venter, responsible for product development at Rijk Zwaan, growers require a great deal more capital to produce tomatoes than 10 years ago.

“Farmers who contemplate planting tomatoes should be prepared to pay more for inputs. In addition, retailers and consumers are demanding a higher quality product, therefore a more intensive crop protection programme is required,” he says.

Wessels highlights that growing tomatoes successfully starts with understanding the crop and its growth stages.

“Tomato plants go through distinct vegetative and generative stages influenced by seasonal changes that result in a constant shift between warm, dry, overcast, or rainy conditions, as well as the difference in day and night temperatures and day length and light intensity.”

In addition, Venter advises that before planting, farmers should secure a market for their produce.

“In the past it was easy to deliver products to the fresh markets in the bigger centres, but with the current situation at some of the markets, this is not [necessarily] a wise strategy to build your business on.

“Tomato producers should ensure that they have a three-market offset strategy that gives them access to supermarket groups or individual stores, the informal market, as well as the fresh produce markets. It will also help farmers spread risk.”

Production stages

Regardless of the variety, all tomatoes follow a biological cycle starting from seed germination to harvesting, with each individual stage of the cycle demanding specific management practices in accordance with the environmental conditions, Wessels explains.

“The six stages are germination, the seedling phase, vegetative growth, flowering, fruit development, and harvesting. By understanding these stages, farmers will be able to provide the optimal conditions for growth and development, and quality products,” says Wessels.

• Germination
  As with many other crops, it all starts with the seed. The inherent potential of the crop lies in the seed.

“How farmers manage the crop will determine yield and quality,” says Wessels.

The right balance of moisture together with soil and air temperature will help the seed to germinate. Special crop care is necessary during the germination period.

• Seedling phase
  Depending on the temperature, it takes about five to 10 days for tomatoes to germinate. Once the cotyledons appear, the seedling stage begins. The cotyledons are crucial for starting photosynthesis as the process provides the energy for the seedling to grow.
  Gradually the plant will begin to develop true leaves and outgrow the containers.
  This is the time to transplant the seedlings.

Root development is often an overlooked factor. According to Wessels, a healthy root system is critical for plant vigour and productivity.

“Ensuring proper irrigation, nutrient balance, and aeration is key for strong root development. A strong root system will enable the seedling to establish properly.”

• Vegetative stage
  During the vegetative stage, the tomato plant’s stems will thicken and foliage will increase. This growth spurt requires a lot of energy, therefore the demand for water and nutrients rises significantly. It is also necessary to start paying attention to providing strong structural support to the plant.

“Trellising and pruning become essential. Pruning is necessary to keep the plant in balance. For indeterminate tomato varieties, which grow continuously, it is advisable to remove some of the suckers to maintain plant shape and size,” says Venter.

• Flowering
  During the following reproductive stages of the plant, nutrient management is crucial, Venter points out.

“Use fertiliser to encourage blooming and to support flower and fruit development. During a plant’s life cycle it has different nutritional needs, and the fertiliser programme must correlate to those needs.”

• Pollination
  There are many factors that can affect pollination. According to Wessels, if conditions are too hot or cold, or if humidity levels are too high, pollination can be affected.
• Fruit development
  After pollination, the flowers will begin to wither, and then small green fruits will emerge. At this point in time the plants needs adequate water to prevent stress.

“Stress during this stage can result in fruit loss. It is important to regularly check the soil moisture and adjust fertigation to support the growing fruit,” states Wessels.

• Harvesting
  Indeterminate varieties that continue to produce fruit throughout the season need constant management and maintenance to ensure a continuous harvest.

“Picking ripe tomatoes signals the plant to produce more fruit, so regular harvesting is part of the ongoing care.”

Making informed production decisions

According to Wessels, there is no single cause for reduced yield or quality in tomatoes.

“Keeping detailed records of past crops may be helpful to identify and manage issues early.”

He lists the following important aspects that prevent yield loss and improve fruit quality:

• It is advisable to select disease-tolerant and adapted varieties for specific areas and conditions;
• Follow a balanced nutrition programme with adequate potassium and proper pH levels;
• Prevent stress during the growing season;
• Avoid unfavourable seasons, especially in open field production;
• Prevent excessive vegetative growth;
• Frequently harvest indeterminate varieties to maintain fruit quality;
• Minimise exposure of the fruit to direct sunlight.

Production methods

Depending on the region, the market, and the variety, tomatoes can be grown under various types of protected environments or in open fields. All methods have unique advantages and challenges. Venter emphasises that it is important to understand the challenges and advantages in order to optimise yields, quality, and profitability.

“The choice between protected or open- field tomato production depends on several factors including budget, climate, market demand, and production goals,” says Venter.

“To produce tomatoes under protection offers higher and more consistent yields and good fruit quality, and enables farmers to produce for a longer period during the year, but requires higher investment and management skills.

“If cost is a factor, open-field farming can be more accessible, but farmers must consider the risks associated with unpredictable weather conditions,” Venter advises.

Protected production
Growing tomatoes in a protected environment involves production under cover in plastic structures or under nets and offers precise control over temperature, humidity, irrigation, and pest management, Venter explains.

Because of the control the grower has over many aspects, production regardless of external weather conditions is also possible as the structures protect plants from extreme weather conditions such as heavy rain, hail, or strong winds that can damage crops in open fields.

As a result of the intense farming practices, farmers typically obtain higher yields and better quality fruit, with fewer blemishes and diseases.

“Continuous production allows farmers to supply markets during off-seasons, often fetching premium prices,” says Venter.

Growers can choose from various greenhouse structures such as plastic tunnels, self- ventilated multi-span greenhouses, climate controlled greenhouses or net houses.

“All of these are suitable for growing tomatoes, and the choice will depend largely on the local environmental conditions, as well as the amount the grower is willing or able to invest. In general terms, we refer to these structures and conditions as low, medium or high tech.”

Venter explains that under high-tech conditions, growers make use of automated climate control, airflow, irrigation, fertigation and moisture control. Controlled environment structures such as plastic greenhouses require higher upfront investment due to construction, heating, ventilation, and labour. It will also require a higher level of intensive management, Venter adds.

“As a grower, you would like to drive high and quality yields from every square metre to get a return on investment.”

According to Wessels, as a rule of thumb, the growth cycles in net or greenhouses are as follows:

• Short cycle: 140 to 150 days from planting to harvest;
• Long cycle: 10 to 11 growing months, including nine months of harvesting.
  In any of the structures that can be used when producing in a protected environment, light intensity remains one of the crucial elements.

“Light directly impacts sugar production, fruit development, transpiration, and overall plant health. Proper nutrient balance at each growth stage is essential to maintain high yields and premium fruit quality throughout the season,” Wessels emphasises.

Open field
In South Africa, the vast majority of tomato production is still conducted in open field conditions where the production relies on natural conditions. The initial capital needed, therefore, is less than for production in a protected environment, and growers may also benefit from lower operational costs since there is no need for complex infrastructure or energy inputs for climate control.

Open-field tomatoes are usually grown seasonally and are subject to weather variability and rainfall. Yield per hectare under open- field production may be lower and more variable due to dependency on weather and increased vulnerability to pests and diseases.
Crop rotation is important when doing open-field production.

“The ideal system is to only replant the same field after three years,” says Venter.

General management practices

Soil preparation
Proper soil preparation improves the potential for profitable production of tomatoes. Primary soil preparation must be aimed at creating growing conditions for tomato plants to develop the optimal root system for a specific soil profile.

“Although the root structure of a tomato plant can penetrate various soil types up to depths of 2m, the highest percentage roots will be found in the top 600mm of the soil.”

Wessels points out that the advantages of soil preparation are:

• No restrictions on root development;
• Less chance of compaction;
• More oxygen in the soil, creating better root development;
• Higher yield;
• Reduction in production costs;
• More vegetative growth;
• Better tolerance to drought and stress;
• Less root disease prevalence;
• Horizontal and vertical compaction layers broken;
• Better water retention;
• Increased uptake of moisture and nutrients.
  The choice of the soil preparation systems should be determined by the requirements of the plant and soil.

Wessels says that no standard soil health system can be recommended on all soil types. The choice of preparation method should be made based on the clay content of the soil.

In addition, soil preparation should be done to depths varying between 200mm and 400mm. Ridging is highly recommended and should be done according to the land contours. The main advantage of ridging a tomato crop is to keep excess water away from the plant, improved oxygenation of the root zone, increased soil depth in the growing bed, and better root development.

• Planting periods
  Wessels notes that there are various factors influencing the decision and timing to plant.

“Temperature has a major effect on plant growth, flowering and fruit set. Tomatoes grow and produce the best when the mean temperatures are between 20°C and 24°C. This is, however, a very general statement, as the effect of high temperature in the day can be offset by a lower night temperature, or in some cases by lower light intensity.”

Plants have the ability to grow well at temperatures well above 30°C, but these temperatures have a negative effect on fruit set.

“The critical factor with regard to fruit set is the night temperature, which should be from 15°C to 20˚C for the optimum set. When the average daily temperature is above 32°C and the night temperature is above 21°C, fruit set is poor. Fruit set generally fails below 13°C.”

According to Wessels, the establishment periods for the main production areas of South Africa will be:

1. Lowveld (frost-free areas) – February to May
2. Middleveld (moderate areas) – September to December
3. Highveld (cold areas) – October to November
4. Western Cape – October to December.

• Trellises
  The space in a greenhouse is prime real estate. Vertical production multiplies the production space and capacity without the need to expand the greenhouse area.

In addition, fruit-bearing plants like tomatoes, cucumbers, peppers, and aubergines can triple their yield when provided with proper support structures.

Indeterminate tomatoes need a robust support system to prevent branch breakage. Quality trellises distribute plant weight evenly across multiple contact points. Trellised plants receive more consistent and even light exposure on all sides of the plant.

The improved light distribution increases photosynthesis and leads to more uniform fruit ripening, and with proper training, better airflow can be obtained in the greenhouse, reducing fungal diseases that thrive in humid conditions.

• Layering
  Layering is a horticultural technique used to extend the tomato growing cycle. It involves carefully lowering the main stem from the top of the trellis and layering it horizontally, allowing new growth to continue upward.

This method enables a single tomato plant to reach lengths of up to 13m while maintaining fruit production at a convenient height for harvesting. Before lowering the plant, all old leaves should be pruned to ensure adequate airflow and reduce disease risk. For best results, create a support structure above your ridges or grow bags to keep stems off the ground and prevent damage.

• Pests and diseases
  Throughout all the growth stages, tomatoes can be infected with various pests and diseases. Proper spacing and crop rotation can help with managing pests.
  The most common and also the most important diseases in tomatoes include:
• Tomato spotted wilt virus (TSWV) is a viral disease that is transmitted by a vector such as thrips.
  “It causes serious losses of economically importance in tomatoes,” Venter notes.
• Fusarium wilt is a soil-borne fungal disease caused by Fusarium oxysporum f. sp. lycopersici, which causes yellowing and wilting. Fusarium will affect the lower leaves of the plant first.
• Tomato yellow leaf curl virus (TYLCV) is a virus from the genus Begomovirus and the family Geminiviridae. “TYLCV is one of the most serious diseases affecting tomato plants, especially in subtropical areas, where it can cause major crop losses,” Venter warns.
• Tomato curly stunt virus is an economically important Begomovirus. “Infected crops portray symptoms such as yellowing, leaf curling, stunting and fruit set reduction,” Venter explains.

According to Venter, it is crucial to consider disease resistance when selecting both varieties and rootstocks. For open-field production, where grafting is less practical, the scion variety should ideally have resistance to TSWV, TYLCV, Fusarium races 1 to 3, and nematodes.

In protected cultivation, where grafting offers a higher return on investment, the rootstock should provide resistance to Fusarium races 1 to 3, nematodes, and, as an added advantage, bacterial wilt. This approach ensures better plant health and long-term productivity.

• Environmental stress
  Environmental factors such as extreme temperatures, inadequate water, or poor soil conditions can stress tomato plants.
  Production under controlled conditions can help to mitigate some of these aspects. By providing shade during hot spells, mulching to retain soil moisture, and ensuring the soil is well-draining and rich in organic matter, stress can be reduced.
• Water management
  The availability of water in the soil is another important requirement for successful tomato production.

“Adequate moisture is necessary for good crop establishment, growth, fruit development as well as quality. To this end, producers must give high-level attention to water availability, irrigation scheduling, and water quality,” says Jovan Erasmus, agronomist at Netafim Southern and East Africa.

“Efficiency in water application is of utmost importance. Water should be applied no quicker than it can penetrate the particular soil or growth medium. If water collects on the surface, it causes soil crusting, and where it starts running off, erosion. You must also know how the water is distributed in the soil, determining how deep and how wide the water reaches,” Erasmus points out.

According to him, growing in a protected environment, especially in soilless media, requires ultimate precision in water and nutrient application.

“The use of advanced compensated non-leakage drippers, combined with multi- channel nutrient dosing equipment, helps to create the perfect root-zone environment.”

Precision irrigation is not only the best solution for the application of water, but also the most efficient method for applying fertilisers.

“Fertigation enables you to deliver nutrients in measured doses, and with perfect timing, to support optimal plant growth and protect your soil from leaching and groundwater contamination.
The quality of the water has a huge effect on the longevity of the irrigation system.
Poor-quality water increases the risk of clogging  the system and drippers, therefore farmers should regularly check the water quality. Drippers must remain open to function at the planned rates,” Erasmus states.

In addition, he emphasises that water quality also has a huge effect on the solubility of fertilisers.

“If the fertiliser does not dissolve, it can clog up the dripper system, and the plants will not receive the nutrients that they need to grow and produce. Yield can be affected as one can lose the entire plant if a dripper is not functioning properly. This is even more critical in a high-tech environment such as hydroponics systems,” he says.

The pH of the water is another aspect that should receive adequate attention. “The pH can also affect the working of fertiliser as well as pesticides, nematicides or fungicides.”

Ensuring the right electrical conductivity, pH, and nutrient levels in the root zone is critical for fast-growing and high-yielding crops. This is especially true when growing in soilless media, since the growing medium has low buffer capabilities and demands a fast and precise reaction.

“You need a system that can react quickly to any change, be it crop stage or climate. This can be the difference between winning and losing. Precision drip systems are based on compensated non-leakage drippers, designed for pulse irrigation and special dosing systems that allow you to keep all parameters exactly where you need them, and react to changes on demand,” says Erasmus.

Irrigation of soilless media is characterised by short irrigation pulses (minutes), and it is advisable that producers over-irrigate by approximately 20% to ensure that salts do not build up in the pots. The additional water will help to leach some of the salts, Erasmus explains.

Under nets in soil this is not important as the systems are normally scheduled to irrigate for longer periods.

“Through technologies such as drip irrigation and real-time monitoring systems, Netafim enables farmers to be more efficient and precise, driving to reduce waste. Drip irrigation is highly efficient as a system. Low-flow drip irrigation systems further allow farmers to irrigate larger areas simultaneously.”

•  Climate management
  According to Wessels, tomatoes are a warm season crop. “It can survive certain amounts of cold units, but are intolerant of very low temperatures. Most importantly, tomatoes require very stable temperature ranges with minimums and maximums not being too wide apart.

“Large temperature variations might result in poor fruit quality or reduced yields,” he states.

“The variation in climatic conditions in South Africa allows the planting and production of good-quality fresh tomatoes in open fields in various parts of the country all year.”

According to Wessels, the minimum temperature for production should be around 10°C, with the maximum being 34°C. Optimum temperatures are around 26°C to 29°C. (The table to the right shows the required temperature ranges per development stage for optimum tomato production.)

• Soil health
  For profitable production, soil health and fertility are key, Wessels advises.

“The quality and quantity of tomato fruits are greatly influenced by the fertility and nutrient levels of the soil.”

He points out that although tomatoes will grow moderately well in a wide range of soil types, in terms of the soil structure and content there are factors that can have a major impact on yield and determine the economic viability of the farming enterprise.

These factors include:

• Nutrient composition;
• Compaction;
• Effective soil depth;
• Soil pH;
• Crop rotation;
• Herbicide residues;
• Water-holding capacity.

“The soil must permit adequate root growth to support the plant and supply water, oxygen and mineral nutrients, and must be free of toxic elements,” he adds.

Wessels explains that the rate of root growth is dependent on the degree of compaction or bulk density of the soil.

“The degree of soil compaction varies with soil type and location. The rate of aerial and root growth of tomato plants increases with the oxygen contents of the soil. Root density is highest where there is a high rate of diffusion. Root development of tomato plants can be extensive if soil water and plant conditions are optimal. They can be as deep as 1,5m and as wide as plant spacing will allow.”

According to Wessels, early root development should be encouraged, because nearly all root growth occurs before fruit set.

In addition, the importance of organic matter in the soil cannot be overemphasised, he notes.

“Organic matter in the form of decayed leaves, compost, sawdust or animal manure is a source of plant nutrients and acts as a soil conditioner. It increases the capacity of the soil to retain water and nutrients. It also promotes root growth and the infiltration of water and air into the soil.”

• Nutrition
  Tomato plants must maintain a balance between leaf development and fruit production. Wessels points out that an imbalance in this relationship can negatively impact yield, fruit quality, and the crop’s longevity.

“Overly vegetative plants yield less than well-balanced plants. Overly thin plants with small leaves may lack sufficient leaf area to produce the sugars necessary for fruit expansion.
“A plant producing 13 trusses with five fruits per truss can gain 1,3kg per plant simply by adding 20g per fruit on average,” Wessels explains.

The ideal temperature range for sugar assimilation in tomato plants is 23°C to 25°C. Deviations from this range will have an effect on the tomato, says Wessels.

Lower temperatures will result in slow ripening and poor colour development, whereas higher temperatures will result in faster ripening, an increased risk of blotchy ripening, and a shorter shelf life.

• Nutritional imbalances
  Nutrient deficiencies or excesses can lead to problems like yellowing leaves or blossom
  end rot. A balanced fertiliser should be used according to the results of regular soil and leave analysis, says Venter.

“Adjusting the fertigation schedule as the plant progresses through its growth stages will also help to prevent imbalances.”

Email the Tomato Producers’ Organisation at [email protected], Werner Wessels at [email protected], or Jandri Venter at [email protected]. Visit rijkzwaan.co.za.