Tomatoes (Lycopersicon esculentum) are herbaceous plants of the Solanaceae family, cultivated for their tasty fruits. Tomato fruits are eaten fresh, prepared, or canned and are rich in vitamins, sugars, amino acids, and organic acids. The chemical composition is influenced by the variety, the pedo-climatic conditions, and the applied technology. The tomato crop can be affected by pests and diseases, against which it’s important to apply the right treatments.

The main diseases of tomato crops

Viruses

Tomato spotted wilt virus

Attacked plants have weakened growth. Leaves are curved downwards and show tan-like spots. Specific, ring-shaped spots can be seen on some leaves. Fruiting is weak and ring-shaped, red or yellow spots appear on the fruit. The virus is transmitted by certain species of thrips.

Prevention and control measures:

• removing and destroying attacked plants from the crop;
• weed control;
• growing resistant hybrids;
• applying insecticides to control the thrips population.

Tobacco mosaic virus on tomato

This virus attacks a wide range of plants, including tomatoes. Affected plants cease to grow and discoloration spots appear on the leaves. Attacked tissues no longer develop normally and leaves shrivel. Leaves develop a mosaic appearance. The plant produces a low number of small, deformed fruits. The virus is transmitted through infected seeds, but also mechanically, through contact between infected and healthy plants.

Prevention and control measures:

• using healthy seeds from safe sources;
• growing resistant varieties;
• removing attacked plants from the crop.

Cucumber mosaic virus in tomato

This virus attacks a broad spectrum of plants, including tomatoes. The first symptom is plant dwarfing. As the disease progresses, the leaves of attacked plants take on a mosaic appearance (alternating healthy green tissue with diseased yellow tissue). The plant also forms filiform leaves (fern leaves). Attacked plants produce small, tasteless fruit. Year-to-year transmission is via infected seeds, and in vegetation, the virus is transmitted through aphids.

Prevention and control measures:

• removing affected plants from the crop;
• using healthy seeds from safe sources;
• applying insecticides to control the aphid population.

Phytoplasmas

Stolbur disease in tomato

This disease has a wide host range, both cultivated and wild species. In tomatoes, the affected leaves remain small and deformed and then turn a purplish color. In flowers, sepals elongate, petals and stamens atrophy and flowers become sterile. Fruits formed before infection remain small, hard, woody, and tasteless. Stolbur disease is spread by the leafhoppers.

Prevention and control measures:

• removing weeds from the crop and from around the plots;
• removing affected plants from the crop;
• applying insecticides to control the pest population;

BACTERIOSIS

Bacterial canker of tomato (Clavibacter michiganensis subsp. michiganensis)

The disease occurs in all stages of development. In mature plants, the first symptoms are leaf twisting towards the top, followed by curling of the main vein and wilting. Leaves may sometimes show wet spots, where the tissues become parchment-like. In wet weather, bacterial exudates appear from wounds on all parts. Fruits remain small and spotted, and the vascular vessels turn brown. Seeds from affected fruit turn brown, have low germination and can transmit the bacteria. The main form of transmission is through infected seed material. During vegetation, the bacterium can be spread by water, tools, etc. The bacterium easily penetrates the plant through wounds resulting from specific maintenance work: suckers pruning, defoliation, pinch out, etc.

Prevention and control measures:

• using healthy seeds from safe sources;
• removing attacked plants from the crop;
• gathering and destroying plant debris after harvest.

Bacterial leaf spot (Xanthomonas campestris pv. vesicatoria)

It attacks all aerial parts of the plant. The disease can appear when the plant is still in the seedling stage. Irregular, greenish-yellow spots appear on the leaves, with a brown central area. In damp conditions, shiny rings appear around the spots, representing bacterial exudate.

In the case of a severe infection, the patches merge and the tissues tear. Cracks of different shapes and sizes may appear on the stems. Fruits show circular, moist spots surrounded by a white-grey ring. Affected tissues become hollow and brittle. As the fruit grows, the tissues tear, and other pathogens may enter the fruit. The bacterium is transmitted from one year to the next via infected seeds and plant debris left on the ground.

Prevention and control measures:

• using healthy seeds;
• disinfecting seeds and substrate for hotbed;
• removing attacked plants from the crop;
• gathering and destroying plant debris after harvest.

Bacterial speck (Pseudomonas syringae pv. tomato)

The disease attacks all aerial parts of the plant. The first symptoms are small, moist-looking, well-defined spots. The attacked tissues dry out and fall off. Affected fruits show small brown spots, bordered by a green area. Ripe fruits are not affected due to their acid pH. The bacterium survives over winter on infected seeds and plant debris on the soil surface. During vegetation, the disease is transmitted by bacterial exudate, which is carried by various vectors (water, wind).

Prevention and control measures:

• disinfecting seeds and substrate for hotbed;
• gathering and destroying plant debris after harvest;
• removing attacked plants from the crop;
• tomatoes treatments with specific fungicides.

Pith necrosis of tomato (Pseudomonas corrugata)

The bacteria attack mature plants in protected spaces. Initial symptoms include plant discoloration and wilting. The attack progresses rapidly and within a few days, brown spots appear on the stem. The stems turn brown and crack, and in humid conditions, bacterial exudate oozes from these lesions. In cross-section, the stem is browned. The bacterium enters the plant through wounds resulting from maintenance work.

Prevention and control measures:

• removing attacked plants from the crop;
• balanced fertilization;
• tomatoes treatments with specific fungicides.

Mycosis

Damping-off (Pythium spp.)

It is the most important seedling disease, attacking all vegetable species. The tissues in the stem’s basal area turn brown. The stem thins in the affected area and the plant falls to the ground, where it rots. The disease spreads rapidly if temperatures and humidity are high. In affected areas, a whitish mold may appear on the soil surface. It is transmitted by spores found in the soil.

Prevention and control measures:

• seedling pricking;
• ensuring optimal ventilation;
• disinfecting seeds and seedling substrate;
• rational irrigation;
• tomatoes treatments with specific fungicides.

Downy mildew (Phytophthora infestans)

This disease attacks tomatoes in all stages of development. The first symptoms consist of wet spots on the upper side of the leaves. The affected tissues turn brown and twist. In conditions of high atmospheric humidity, a greyish fuzz appears on the underside of the leaves, opposite the spots.

Leaf petioles, leaf blades, and stems may show brown, elongated spots. Attacked inflorescences wither and fall off. The fungus also attacks fruit, causing significant damage. The fungus enters the fruit through the stalk area and produces large brown spots. The fruit becomes hard, and rough and forms concentric zones in the affected area. During vegetation, it spreads by vectors (water, wind, animals, tools, etc.).

Prevention and control measures:

• isolating tomatoes from potato crops;
• polytunnels ventilation;
• avoiding sprinkler irrigation;
• gathering and destroying plant debris after harvest;
• removing affected plants from the crop;
• tomatoes treatments with specific fungicides.

Phytophthora root rot (Phytophthora parasitica)

This disease frequently occurs in protected spaces. It can also appear in the field in years with high soil temperatures. This disease produces symptoms similar to Pythium spp. (damping-off), but this pathogen attacks plants at a more advanced stage of development.

The first signs of attack consist of plant browning and wilting. The basal leaves turn yellow and the stem produces adventitious roots. Greyish-green spots appear on the fruit, with diffuse margins and concentric areas. Eventually, the fruits acquire a rotten appearance and fall on the ground. The fungus survives in the soil, and during vegetation, it is transmitted by spores carried by water droplets.

Prevention and control measures:

• ensuring optimal ventilation;
• seedling pricking;
• disinfecting the seeds and seedling substrate;
• rational irrigation;
• tomatoes treatments with specific fungicides.

Powdery mildew (Leveillula taurica)

The fungus attacks all aerial organs of the plant, but evident symptoms can be seen on the leaves. The attack starts on the basal leaves, which are covered with a white powder. The affected tissues turn brown and the leaves dry out completely. Affected plants form a small number of fruits, which mature very slowly. The fungus causes significant damage in protected areas. In winter, the fungus spores live on plant debris on the soil surface. During vegetation, infection is transmitted by spores carried by water droplets.

Prevention and control measures:

• avoiding sprinkler irrigation;
• removing affected plants from the crop;
• polytunnels proper ventilation;
• balanced fertilization;
• gathering and destroying plant debris after harvest;
• tomatoes treatments with specific fungicides.

White mold (Sclerotinia sclerotiorum)

This fungus develops in field crops but causes the most damage in protected areas. Moist, brown spots appear at the base of the stem. These are covered by a white fuzz in which the fungus sclerotia develops. The attacked tissues rot and the plant withers. In excessively humid conditions, the fruits are also attacked and fall off the plant. The fungus survives in the soil as sclerotia.

Prevention and control measures:

• rational irrigation;
• crop rotation (tomatoes can return to the same field after 3-4 years);
• removing attacked plants from the crop;
• carrying out sucker pruning and defoliation works;
• tomatoes treatments with specific fungicides.

Septoria leaf spot in tomato (Septoria lycopersici)

Circular brown spots appear on tomato leaves, the attacked tissues turn grey, and small, blackish-brown dots develop on them, representing the fungus fructifications. The attacked areas are delimited from the healthy areas by a brown margin. The fungus spreads by spores carried by wind, water, etc. The fungus survives in winter on plant debris on the soil surface.

Prevention and control measures:

• gathering and destroying plant debris after harvest;
• planting healthy seedlings;
• tomatoes treatments with specific fungicides.

Corky root rot (Pyrenochaeta lycopersici)

The roots of attacked plants are thickened (suberified) and brown. Attacked tissues have a spongy consistency, popularly called “cork roots”. The aerial parts of the plant turn yellow, fruit poorly, and finally wither. The fungus lives in the soil on the affected roots, which are the main source of infection.

Prevention and control measures:

• disinfecting seedling substrate;
• correct crop rotation (tomatoes can return to the same field after 3-4 years);
• the treatments applied against the damping-off and against phytophthora root rot can be used against this disease.

Anthracnose (Colletotrichum coccodes)

The disease occurs in the field in hot, rainy years. The fungus infects the fruit since it is green, but the symptoms appear when it begins to ripen. On their surface appear small, circular spots near which the tissues sink. As the disease progresses, concentric areas appear on the spots’ surface. Black spots form under the fruit skin. Small black spots may appear on the leaves. On roots, the attack manifests as a dry rot.

Prevention and control measures:

• disinfecting substrate for hotbeds;
• correct crop rotation (tomatoes can return to the same field after 3-4 years);
• rational irrigation;
• tomatoes treatments with specific fungicides.

Tomato early blight (Alternaria solani)

Tomato plants can be attacked in all stages of development. Isolated brown spots with concentric areas appear on tomato leaves. In a strong attack, the spots enlarge, and merge, causing partial or total defoliation. Dark spots appear on the stems, slightly sunken into the tissue. On fruit, the disease first appears in the stalk area, where small, concentrically spots appear, slightly sunken into the tissue. The disease is transmitted through affected plant debris and infected seeds.

Prevention and control measures:

• growing resistant or tolerant varieties and hybrids;
• using healthy planting material;
• gathering and destroying plant debris after harvest;
• weed control;
• tomatoes treatments with specific fungicides.

Gray mold (Botrytis cinerea)

This fungus attacks tomatoes grown in the field and in protected spaces under low light and high humidity conditions. Symptoms of this disease can be seen on stems, leaf petioles, flowers, fruit, and leaves. Brown areas appear at the base of the stems, slightly sunken into the tissue. The affected parts become covered with a gray fuzz that eventually destroys them. Attacked flowers rot and become covered with a gray fuzz. If humidity remains high, the disease affects the almost ripe fruit. The attack manifests as watery spots, which become covered with a gray fuzz. After the attack, the fruit is destroyed. The fungus lives on plant debris on the soil surface and its spores are carried to healthy plants by air drafts and water droplets.

Prevention and control measures:

• removing attacked plants from the crop;
• gathering and destroying plant debris after harvest;
• polytunnels proper ventilation;
• rational irrigation;
• tomatoes treatments with specific fungicides.

Tomato leaf mold (Passalora fulva sin. Cladosporium fulvum)

The disease manifests mainly on the leaves, where discolored, slightly yellowish spots appear on the upper surface. On the underside of the leaf, a dense, brown mold appears. In case of a strong attack, the affected areas enlarge and merge, causing the leaf to dry out. The disease is spread by spores which are carried by vectors (water, wind, etc.).

Prevention and control measures:

• polytunnel proper ventilation;
• growing resistant tomato varieties;
• gathering and destroying plant debris after harvest;
• tomatoes treatments with specific fungicides.

Verticillium wilt (Verticillium dahliae)

This disease produces evident symptoms in the ripening phase of the fruit. Yellow, marginal, or central areas appear on the leaves and dry out. The plants wilt during the day and look normal in the evening. However, after a few days, wilting is irreversible. Affected plants bear less fruit and the fruit is of poor quality. If a section is made through the vascular vessels of the attacked plants, the fungus mycelium can be seen blocking the sap circulation. Verticillium can easily be confused with Fusarium wilt, having similar symptoms. The fungus lives in the soil, and when environmental conditions are favorable, it can penetrate the plant through wounds produced at the root level.

Prevention and control measures:

• growing resistant varieties;
• removing attacked plants from the crop;
• disinfecting seeds and hotbed substrate;
• rational irrigation;
• tomatoes treatments with specific fungicides.

Physiological disorders

In addition to disease symptoms, tomatoes may show physiological changes caused by growing factors (water, temperature), fertilizers, herbicides, or pesticides. These can be easily confused with disease symptoms. Correct identification of diseases, pests, or deficiencies is very important to obtain a rich and healthy crop.

Sunscald

This change occurs in hot summer months when solar radiation is intense. Tomato fruits exposed to direct sunlight acquire a milky-grey color, they stop ripening and become hard.

Prevention methods:

• installing special shading nets;
• creating protective curtains around tomato crops by sowing tall plants (maize).

Calcium deficiency

Calcium deficiency is manifested by plant growth stagnation, leaf margin browning, and drying of growing tips. The most visible and easily noticeable symptom is seen on the fruit, with the appearance of apical rot (a specific brown spot appears on the fruit tip). This area may be infected by plant pathogens.

Prevention methods:

• balanced fertilization;
• applying foliar fertilizers to adjust microelement deficiencies.

Zippering

This disorder manifests as brown scars that extend over the entire fruit, with a zipper-like appearance. If the fruit grows suddenly, it may crack in the scar area. This disorder appears in low-temperature conditions.

Prevention methods:

• ensuring the optimal temperature in the protected spaces;
• rational irrigation.

Hydric stress

In case of lack of water, plants have slowed growth and show wilting symptoms on the leaves. If the plants are not supplied with water, they may dry out completely. If dry periods alternate with periods of excess moisture, the fruit may show symptoms of cracking in the stalk area, where pathogens can settle.

Prevention methods:

• maintaining constant soil moisture;
• periodic crop control.

Fruit deformities

Fruit physiological deformations usually occur in the lower part of the fruit (opposite the peduncle). In most cases, they are represented by holes and cracks but can have different shapes and sizes. These abnormalities occur during fruit formation in low temperatures.

Prevention methods:

• rational fertilization;
• assuring good environmental factors;
• maintaining constant soil moisture.

The main pests of tomatoes

European mole cricket (Gryllotalpa gryllotalpa)

This pest has an omnivorous diet, feeding on plant substrate, live prey ( earthworms and various larvae), or insects. It causes damage by gnawing seeds or tomato plant root systems.

Control measures:

• carrying out treatments with specific insecticides.

American serpentine leaf miner (Liriomyza trifolii)

It is a polyphagous species that attacks almost all vegetable species. The leaf miner fly has 6-8 generations per year and overwinters as a pupa in the topsoil. The larvae gnaw the leaves in the form of mining galleries. In case of a strong attack, the leaf area is reduced, with consequences for crop yield.

Control methods:

• carrying out treatments with specific insecticides.

Nematodes

They are microscopic pests that attack most vegetable species. They develop numerous generations per year and multiply very quickly. The larvae penetrate the plant root system and settle in the root vessels. During feeding, they secrete a toxin that causes tissue hypertrophy. Attacked tomato plants stagnate in growth and eventually wither.

Control methods:

• correct crop rotation;
• growing resistant tomato varieties;
• disinfecting the soil with specific products.

Aphids

They are polyphagous species, migrating from one plant to another or from one species to another. Aphids grow on wild flora and then move to cultivated species. They are found as colonies on the underside of leaves, on flowers or inflorescences, and young shoots. Attacked plants stagnate, turn yellow, and become susceptible to fungal attack. After feeding with plant sap, the aphids cover the leaves with their sweet droppings, forming the so-called ‘honeydew’, which allows saprophytic fungi to settle and form sooty mold.

Control methods:

• using sticky traps;
• specific insecticide treatments.

Thrips

They are small pests, hardly visible to the naked eye, that attack a very large number of crop plants. They colonize the growth tips, flowers, and leaves, causing flower abortion and plant dwarfing. Thrips can be vectors for the transmission of certain viruses.

Control methods:

• using sticky traps;
• carrying out treatments with specific insecticides.

Red spider mite (Tetranychus urticae)

It has 6-10 generations per year and overwinters as an adult, especially as females (males are generally rarer), under the exfoliated bark of trees, under fallen leaves, on dry weeds, or in the surface layer of the soil. Attacked leaves show specific symptoms of chlorotic spots, caused by the mites feeding on plant sap. After the attack, plants stall growth, leaves dry out and the plant may be compromised.

Control methods:

• specific insecticide treatments.

Greenhouse whitefly (Trialeurodes vaporariorum)

The pest thrives in greenhouse conditions all year round, and in the field only in summer. In the greenhouse, it can develop 3-6 generations when conditions are favorable. Adults and larvae colonize leaves, often the shoots. After the attack, leaves turn yellow, dry out, and fall off.

Prevention and control methods:

• destroying plant debris after harvest;
• disinfecting greenhouses and polytunnels before starting a new crop;
• using sticky traps;
• specific insecticide treatments.

Slug (Deroceras agreste)

It is a polyphagous species, that attacks many vegetable plants, flowers, vines, etc. It causes great damage to vegetable crops by eating the leaf parts. In case of a strong attack, the entire plant foliage can be destroyed.

Control methods:

• chemical treatments with specific insecticides.

Tomato leafminer (Tuta absoluta)

It has several generations per year and overwinters as a nymph in the soil. This pest attacks all vegetable species of the Solanaceae family (potato, aubergine, peppers), but prefers tomatoes. The larvae penetrate the leaves and consume the area between the upper and lower epidermis. The larvae also attack the stem or petiole of the leaves and fruit, leading to quality depreciation.

Prevention and control methods:

• gathering and destroying plant debris after harvest;
• performing tomato treatments with specific insecticides.

Cotton bollworm (Helicoverpa armigera)

It is a polyphagous species, attacking more than 120 plant species. The pest attacks vegetables grown in protected areas, but also those grown in the field. The moth develops two generations per year and overwinters as a nymph in the soil. The larvae gnaw the leaf epidermis and then enter the fruit where they consume the flesh and seeds, causing the fruit to decay. One larva can destroy up to 10 fruits.

Control methods:

• tomatoes treatments with specific insecticides.

Southern green stink bug (Nezara viridula)

It has two generations per year and overwinters as an adult under fallen leaves on the ground. It causes significant damage to tomato crops, stinging the fruit and causing its depreciation. The pest can transmit different pathogens from one plant to another.

Control methods:

• performing treatments with specific insecticides.

Lasioptera spp.

The pest mainly attacks crops in protected areas. Adults lay eggs on wounds produced by pruning, and defoliation, from where larvae enter the stem, where they feed. Symptoms of attack can be mistaken for the appearance of a mold disease. Attacked stems split and the plants wilt. The females may also lay their eggs on the fruit of tomatoes, from where the larvae enter the fruit and depreciate its quality.

Control methods:

• performing treatments with specific insecticides.

Bean seed fly (Delia platura)

It is a polyphagous species that attacks almost all vegetable plants. It has 2-3 generations per year and overwinters as a pupa in the soil. The adults emerge in early spring and lay their eggs in the soil near the plants. After hatching, the larvae attack germinating seeds, in which they dig feeding galleries.

Control methods:

• performing treatments with specific insecticides.