Methods for controlling Fusarium wilt and diagnosing tomato grey mould

Soil restoration and management of tomato Fusarium wilt

Following chemical or thermal soil disinfection in greenhouses, it is mandatory to perform microbiological recultivation. In domestic practice, Trichoderma is most often used to restore microflora. However, the efficacy of protective measures can be significantly increased by expanding the range of biological products applied.

Good results are achieved by the combined application of a complex of beneficial microorganisms:

• Planriz;
• Baktofit;
• Trichoderma;
• Gliocladium;
• nematophagous fungi.

For the direct control of Fusarium wilt, both biological and chemical agents are used. Among biological products, treatments with Phytolavin-300, Alirin-B, and Immunocytophyte show high efficacy. As for chemical protection measures, fungicides from the benzimidazole group are applied. For preliminary soil disinfection against a complex of fungal diseases, including Fusarium wilt, Basamid-granulate is used.

Diagnosis and control of tomato gray mold

The causative agent of the disease is the wound pathogen Botrytis cinerea Pers. The infection affects plant stems through mechanical damage caused during cultivation. In humid weather, the fungus quickly spreads to inflorescences, fruits, and shoot tips. The primary source of infection is often neighboring cucumber or lettuce plantings, while the pathogen itself is spread throughout the greenhouse by wind, contact with plants, and water splashes during irrigation.

• Onset of infection — from the fruiting phase
• Spot growth over 3–5 days — up to 4–5 cm
• Period without sporulation — the first 6–8 days
• Appearance of gray mold — after 7–10 days
• Stem mortality by the end of August — half or more

Symptoms of infection with gray mold develop in a strictly defined sequence:

1. Brown spots appear on the root collar of seedlings, leading to the death of the sprouts. On the cotyledons and leaves of young plants, grayish-brown spots with gray mold form.
2. In April–May, brown spots appear on the stems of mature plants at the sites of broken petioles or fruit clusters.
3. The spot expands along the length of the stem, covering its entire perimeter. The center of the lesion lightens to a straw color, and blurred ring-shaped stripes appear on it.
4. Necrosis of the vessels and bark begins inside the stem. This blocks the movement of sap, causing the part of the plant above the spot to wilt, and numerous adventitious roots form on the stem itself.
5. An ash-gray conidial mold of fungal sporulation grows on the affected areas. Small black sclerotia form on plant debris at the end of the season, which preserve the infection in the soil.

There are no tomato hybrids completely resistant to gray mold, although Piligrim and Vasilievna hybrids show relative tolerance.

For reliable disease control, a complex of agrotechnical measures is used:

• maintaining low humidity in cultivation facilities;
• removing leaves and shoots only in dry weather and using only a sharp knife to reduce the wound surface;
• mandatory cleaning of the greenhouse from plant debris;
• timely diagnosis and painting of affected stem spots with fungicide pastes in the early stages of the disease.

Products and treatment schedules against gray mold

To protect tomatoes from the stem form of gray mold during the growing season, growth regulators, biological products, and chemical fungicides are used. Treatments with sodium humate suppress disease development and reduce its spread on tomato hybrids. Among biological agents, Baktofit is used, which is suitable for both prevention and treatment of plants.

• Reduction in gray mold spread by sodium humate — 1.5–2.2 times
• Biological efficacy of sodium humate — 48.9–54.7%
• Fungicide dose in paste per 10 L of water — 30–40 g
• Consumption of CMC glue for the paste base — 300–340 g

Preventive treatment of stems with a Trichodermin suspension effectively suppresses the development of secondary disease foci. Spraying is especially important immediately after leaf removal. If wet spots have already appeared on the stems, they are spot-treated with a suspension of Trichodermin spores—this method is labor-intensive but provides a long-lasting protective effect. Furthermore, a natural antagonist of the pathogen is often found in greenhouses—the saprophytic fungus Botryosporium pulchrum, which colonizes Botrytis cinerea and suppresses disease development.

After harvesting harvesting, greenhouse structures and glazing are disinfected, and the soil is either steamed or fumigated. During the growing season, it is important to regularly inspect plants to identify primary infection sites, especially after leaf pruning in damp weather. Upon detecting the first spots, they are locally treated with Rovral, Efal, or Tecto fungicides. Full-coverage treatments are only necessary if the primary sites were neglected and the disease has begun to spread rapidly and sporulate.

To prevent a grey mold epiphytotic in greenhouses, it is recommended to follow this treatment schedule:

For local smearing of affected stem areas, prepare a protective mixture based on glue:

1. Dissolve 300–340 g of CMC glue in 10 L of water.
2. Add 30–40 g of fungicide (Rovral, Sumilex, Bayleton, or Topsin-M) to the solution.
3. Bring the mixture to a paste-like consistency by gradually adding chalk or lime.
4. Carefully smear the spots, covering 2–3 cm of outwardly healthy tissue around the site.

Prevention of white mold and Ascochyta blight in tomato

The causative agent of white mold (Sclerotinia sclerotiorum) moderately damages the tomato crop, mainly affecting fruits during harvesting and storage at the sites of skin cracks. On stems, shoots, and leaves of mature plants, signs of the disease appear from the start of fruit formation on the first cluster. Affected tissues become slimy and covered with a white, cottony fungal bloom, in which flat or round black sclerotia with a diameter of 1–3 cm are formed.

The main emphasis in combating white mold is placed on thorough disinfection of greenhouses after the end of the crop rotation and the use of thermally disinfected compost. Dormant pathogen sclerotia are completely destroyed during soil steaming, as well as during treatment with Basamid-granules or methyl bromide. When switching to a low-volume growing technology, the problem of white mold on tomatoes does not arise.

Ascochyta blight, or stem canker (causative agent Ascochyta lycopersici, sexual stage Didymella lycopersici), appears in glass greenhouses in late summer and autumn during prolonged rains. In plastic greenhouses, the disease can cause mass plant losses. In such conditions, a large part of the surrounding bushes dies rapidly, which leads to significant harvest losses.

Ascochyta blight of tomato: diagnostics and control measures

Ascochyta blight predominantly affects tomato stems, less frequently spreading to leaves, while on flowers and fruits it appears mainly in open fields. The disease begins at the base of the stem with small depressed brown spots, which then secrete droplets of gum and turn grey. Over time, the stem is encircled by small necrotic spots with black dots of pycnidia. Leaves react to the infection with small, round, brown spots with a light-yellow border of chlorotic tissue.

When flowers are affected, they remain underdeveloped. Dark depressed spots with a brown border appear on the fruits; they gradually lose turgor and mummify. Depending on weather conditions, fruit rot develops in a dry or wet type, and their surface becomes abundantly covered with black pycnidia. The infection persists primarily on seed and plant residues.

• Pycnidia diameter — 100 х 270 µm
• Pycnospore size — 6–11 х 3–7 µm
• Trichodermin in the paste recipe — 30%
• Na-CMC in the paste recipe — 3–5%
• Milk in the paste recipe — 20%

For prevention, it is necessary to thoroughly clean greenhouses of plant residues, disinfect containers and tools, and decontaminate the soil by steaming or using Basamid-granules. It is important to regularly inspect plants in high-risk zones — under dripping areas or near damaged side glazing. The first diseased plants discovered should be removed from the greenhouse as carefully as possible. Maintaining an optimal temperature and humidity regime, especially in the autumn period, and reliable roof glazing ensure minimal disease development.

To prevent a disease outbreak, avoid prolonged cooling of plants combined with high humidity. Ventilate greenhouses regularly, reduce the irrigation rate, and increase the temperature using overhead heating pipes. For treatment, affected stems are coated with special pastes or sprayed with fungicides.

• Application of biological preparations (e.g., Trichodermin) to the soil after disinfection;
• Spraying of affected plants with the biological preparation Alirin-B;
• Coating or spraying of stems with preparations based on Trichoderma and Gliocladium (for coating, a paste is prepared: Trichodermin + Na-CMC + milk + water);
• Treatment of affected spots with chemical fungicides Quadris or Bordeaux mixture;
• Coating of spots with a paste based on a mixture of chalk and fungicides Rovral or Sumilex (in personal subsidiary plots, the use of copper- and sulfur-containing preparations is permitted).

Southern blight: protection of transplants and fruits

The disease is caused by pathogens Phytophthora cryptogea and Phytophthora nicotianae. Southern blight is most dangerous in soil-based greenhouses with a low level of agricultural practices. It causes maximum damage in early spring during the growing of transplants and during the filling period of the first fruits.

The pathogen Phytophthora cryptogea is found only in unsteamed soil-based greenhouses and affects the root collar of transplants. Its outer tissues blacken, soften, and a constriction forms on the stem, after which the plant wilts and rots. Over time, the lesion moves higher up the stem, covering it with a white or brownish mycelial growth. On mature plants, this pathogen can cause rot of roots, stems, leaves, and fruits.

The pathogen Phytophthora nicotianae damages the fruits of lower clusters that come into contact with the soil. On tomatoes, grayish-green, and later light-brown, zonal spots form, and the fruit tissue itself becomes watery. A weak growth forms on the surface, after which the fruits easily drop off.

• Size of Ph. cryptogea zoosporangia — 24–50 x 17–30 µm
• Diameter of Ph. cryptogea oospores — 25 µm
• Ph. nicotianae zoosporangia on the stem — 27.9–52.7 x 21.7–40.3 µm
• Ph. nicotianae zoosporangia on fruits — 56–100 x 28–40 µm
• Application rate of Pseudobacterin-2 for seed — 1–1.5 l/kg

Fruit infection occurs when contaminated soil gets on them. To prevent harvest losses, carry out protective measures strictly in order.

1. Perform thermal steaming or chemical sterilization of the soil before the start of the season.
2. Soak seeds in a solution of the preparation Pseudobacterin-2 to eliminate seed infection.
3. Drench growing plants with a working solution of Pseudobacterin-2 in seedling trays or cassettes.
4. Repeat the drenching of plants with a working solution of Pseudobacterin-2 after planting the transplants into the soil.
5. Regularly collect and remove all affected fruits from the greenhouse to prevent the spread of infection.

Irrigation of transplants immediately after planting in the greenhouse with a 0.01% solution of sodium humate reduced its incidence of southern blight by 4.3-5.5 times, and spraying reduced the incidence of fruits in all cultivars by 1.3-1.4 times. That is, protecting the tomato from the more harmful stem form of southern blight was more effective than protecting the fruits. The biological effectiveness of sodium humate in the first case was twice as high as that of copper oxychloride, 40.3-83.5% and 35.2-40.7%, respectively.

Among chemical agents, copper-containing preparations have low effectiveness: copper oxychloride, copper oxichloride, and Bordeaux mixture. 2.2.3.9. Late blight of Solanaceae. Pathogen — Phytophthora infestans (Mont.) de Bary. Harmfulness. An extremely harmful disease, especially in unheated and damp plastic greenhouses. Leaves, stems, and then fruits turn black. Affected plants soon die, and fruits lose their marketability, and externally healthy fruits also rot during storage and transportation. Fig. 115. FRUIT LATE BLIGHT [IMAGE DATA OMITTED] Fig. 114. Phytophthora infestans ON TOMATO LEAVES [IMAGE DATA OMITTED] Fig. 116. STEM FORM OF LATE BLIGHT OF SOLANACEAE [IMAGE DATA OMITTED] Symptoms. Leaves, stems, and fruits are affected. Large necroses of various shapes, blurry, brownish-brown with a lighter border appear on leaves and fruits. In humid conditions, a weak whitish mycelial growth with zoosporangia soon appears on the affected tissue, forming more often on the underside of the leaves. The stem form of late blight is less widespread than the leaf form and is still rarely encountered. Spots of irregular shape, often merging, dark brown in color, form on stems and petioles. They resemble damage from southern blight, but differ in the time of appearance (end of summer-autumn), whereas southern blight, as a rule, causes damage in the winter-spring period.

Pathogen biology. Zoosporangiophores are weakly branched, have 1-4 main branches and several lateral ones with thickenings at the sites of zoosporangia formation. Zoosporangia are unicellular, ovoid or lemon-shaped, 25-30 x 15-20 µm, colorless, with a thin smooth wall, and a clearly visible papilla at the apex. Oospores are spherical, 30 µm in diameter, colorless, with a wall 3 µm thick. Spores are easily carried by wind and water droplets. The pathogen usually enters greenhouses from open ground from potato plantings or if internal farm quarantine is violated.

The pathogen is not capable of long-term existence in the soil: it is quickly displaced by soil microorganisms. It was generally accepted that the life cycle includes the overwintering of mycelium on stored potato tubers, and the development of epiphytotics on tomatoes was explained by the introduction of pathogen spores from potato plantings. However, accumulated data on the differences between tomato and potato populations of the pathogen contradict this. There are grounds to believe that overwintering occurs in the form of oospores (in the soil on plant residues or on seeds). This oomycete is known to have two mating types: A1 and A2. As a rule, oospores are formed upon contact between the mycelia of strains with different mating types. However, self-fertile strains are also known that are capable of forming oospores without contact with the mycelium of the opposite mating type. From the beginning of the disease's spread in Europe until recently, all studied strains of P. infestans belonged to the A1 type. The A2 type existed only in its historical homeland — Mexico, but recently strains of this type are increasingly encountered in European populations.

Host plants. Various representatives of the Solanaceae family, including potato and eggplant.

Spread and survival of the pathogen. Sources of primary infection include potato plantings affected by this pathogen, as well as oospores surviving in the soil and plant residues. Moreover, oospores pose a great danger. This should be taken into account by those who practice growing tomatoes for many years in the same areas.

Control measures. Agrotechnical practices:

• Create conditions in the greenhouse with a relatively dry climate.
• Promptly remove affected plants.
• Prevent the introduction of infected potatoes into the greenhouse.

Late blight-resistant hybrids of cocktail tomatoes have been obtained. Tolerant hybrids are also known, for example, Semko-99 and Celsus.

Biological agents:

• Plants are sprayed or watered after planting in the soil with a working solution of pseudobacterin-2.
• During the growing season, plants are sprayed with a 0.5-1% working solution of baktofit for prevention and upon the appearance of the first signs of the disease at eight-day intervals.

Treatments with alirin-B, agat-25, and planriz are effective to one degree or another in combating this disease.

Chemical agents. Plants are treated preventively during the period of heavy rains. When the first foci appear, the concentration of the working solution is increased. High-volume spraying of plants with such fungicides as Ridomil MC, Acrobat MC, Sandofan, Oxychom, Quadris, and Strobi is recommended.

In private household plots, one can also use Bordeaux mixture, copper oxychloride, and Curzate. The concentration of the working solution is determined based on the stage of disease development and the application guidelines for a particular pesticide. Repeat spraying when fresh spots appear.

Spraying schedule:

1. The first time, plants are sprayed before the onset of the dangerous period (in the Central region — before mid-July) with such preparations as Quadris or Strobi.
2. The second spraying — upon the appearance of the first symptoms of the disease, using mixed fungicides at intervals of 7-10 days depending on weather conditions.

Powdery mildew. This disease is caused by several ascomycete fungi, but the external manifestation of the disease is similar. Their description is given below. Control measures for them are also the same.

Pathogen — Oidium erysiphoides Fr. Ascomycete stage — Erysiphe communis Grev. f. lycopersici Lasl.

Harmfulness. Pathogens can severely weaken plants, resulting in a noticeable decrease in their yield. As a rule, the disease affects tomatoes in the summer, but if there are weeds in the greenhouse, the infection can persist, which leads to early contamination and large harvest losses.

Symptoms. O. erysiphoides forms a white powdery coating on the leaves in the form of white rounded colonies. As the disease develops, they merge. Gradually, chlorosis of the leaf tissue turns into necrosis. Damage to stems and petioles is observed only with a high degree of disease development.

Fig. 117. TOMATO LEAF DAMAGE BY POWDERY MILDEW.

Pathogen biology. In protected ground, only the conidial stage of the pathogen develops. In greenhouses in the central part of Russia, the disease usually appears in April-May. It has been noted that the first foci of powdery mildew are often associated with the introduction of spores by wind from outside. If disinfection of greenhouses has not been carried out, the emergence of the first foci is possible even in the seedling department due to the presence of viable spores. The development of the parasite leads to a disruption of transpiration and cell photosynthesis. Soon, the leaves begin to dry from the edges and, in the absence of control measures, die off.

On the plant surface there is a mycelial bloom, represented by mycelium with conidiophores and conidia. The colorless conidia are in chains on short conidiophores, cylindrical or ellipsoidal in shape, sometimes barrel-shaped, measuring 30-40 x 15-20 µm.

In the dried-out areas of the leaf, the intracellular mycelium dies, and no new spores are formed. The development of the disease is suspended.

The pathogen is Oidium taurica. The ascus stage is Leveillula taurica.

Symptoms. Yellow spots initially appear on the upper side of the leaves, and a powdery bloom appears on the lower side. Subsequently, the powdery bloom also appears on the upper side of the leaves.

Pathogen biology. Conidia are on long conidiophores, colorless, solitary, elongated-elliptical in shape with a pointed tip. The pathogen develops well at low relative humidity of the air. The development of an epiphytotic occurs at a temperature of 15-25° and with insufficient irrigation.

Biology. The pathogen was noted in the 1990s in the Leningrad Region. It differs from other species by very short conidiophores with a small oval-ovoid conidium.

Dissemination and survival of pathogens. The infection is spread aerogenically by conidia, which are easily carried by air currents. The pathogens infect certain greenhouse crops on which they can overwinter (pepper, eggplant and cucumber). Until the next season, the pathogens can survive in the greenhouse on sow thistle. Protection measures. Agrotechnical practices. Remove weeds in a timely manner, and disinfect greenhouses and substrate between rotations. Upon detection of the first centers of infection, increase, if possible, sprinkler irrigation and irrigation of plants and reduce, as much as possible, drafts.