The Main Diseases Of Tomatoes And How To Deal With Them

2024 Author: Sebastian Paterson | [email protected]. Last modified: 2023-12-16 13:47

Late blight, septoria, mycoses, bacterial cancer, black bacterial spot

Late blight

On private plots in closed (greenhouses and greenhouses) and open ground, the greatest danger from fungal diseases of tomato is late blight, alternaria and septoria, from bacterial - bacterial cancer and black bacterial spot.

Late blight observed almost every season sometimes ruins most of the tomato crop. It is especially harmful if cold dew comes in early August, and gardeners use varieties that are not resistant to this disease for growing. The infectious origin of this mycosis persists on plant debris, but often tomato plants become infected (after 2-3 weeks) from the potato tops already affected by the disease, since they have one pathogen.

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Late blight affects all aerial parts. Its first signs are noted more often on the upper tiers of leaves, from where the disease descends to the lower ones. Large brown spots appear on the leaves, usually located along the edge of the leaf blade. At high air humidity (75-80%), the fungus forms a mycelium in the form of a light white cobweb on the lower part of the diseased leaf. Affected leaves dry out quickly.

Elongated dark-brown spots appear on the petioles and stems, often this leads to the formation of constrictions on the stems, which leads to the early death of the plant. On fruits, symptoms of the disease are visible in the form of rot (brown round spots). With early damage, the fruit may look ugly, but the surface and internal tissues remain hard to the touch. When infected during the filling period, the fruits do not ripen, sometimes they completely turn black within 2-3 days and are no longer suitable for nutrition.

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In the absence of signs of mycosis on the fruits of a diseased plant, the symptoms can soon appear already during the period of their ripening or storage. According to experts, infection of healthy fruits from sick fruits usually does not occur during storage. Late varieties of tomato or belatedly planted plants are more affected.

The most favorable conditions for the rapid development of late blight are those conditions when in the second half of the tomato growing season the daytime temperature is high enough (20 … 22 ° C), and the night temperature is low (10 … 12 ° C). This temperature drop causes dew to fall out, which contributes to the active development of the mycelium, leads to abundant sporulation of the pathogen and the subsequent infection of plants. Most often outbreaks of late blight occur after prolonged rainy weather.

Septoria (white spot) is most harmful in wet years. Dark dotted spots appear on the leaves and stems (less often on fruits) of tomato, which gradually increase in size. They take on an off-white hue and are surrounded by a dark purple border. Black dots (pycnidia) are clearly visible in their center. With a strong defeat of septoria, the spots merge, the leaves dry out and fall off. Mycosis begins with older leaves that are most susceptible to white spot. Its development is favored by humid and warm weather. Affected plants may dry out. The severity of the disease increases in the second half of summer. Plant residues are the source of the disease.

The first signs of Alternaria on plant leaves are signaled by the appearance of large brown spots with concentric circles on their lower tiers. The stems are affected later: they die off or dry rot develops on them. In some cases, depressed rounded spots are fixed on the fruits of a tomato near the stalk.

Fight against tomato mycoses

To prevent the appearance of tomato mycoses, experts recommend not placing tomatoes in the place where you grew potatoes last year, if possible, they are not even placed next to each other. Among the agrotechnical methods in the fight against mycoses include the choice for growing highly resistant hybrids and early varieties (in the zone of increased severity - ultra-early ripening, which have time to yield before the mass spread of the disease).

Varieties resistant to Alternaria are considered to be Alena, Beefsteak, Gold Brandy, Buratino, Olympic Fire and the Golden Andromeda hybrid. The variety Generosity is characterized by immunity to septoria. The varieties Viza, Vityaz 991744, Dar, Persey are characterized by tolerance to these two mycoses. Increased resistance to late blight in varieties Gnome, Gonets 13, Grand, Polyarnik, Chelnok, Yubileiny Tarasenko and hybrids Gunin, Zhenaros, Celeus and Yurand.

The varieties Boyan, De Baro are weakly affected by this disease; tolerant hybrid Viscount. The Ladoga and Yamal varieties avoid late blight due to their early maturity. It is important to observe crop rotation (the return of the crop to its original place not earlier than 3-4 years and not to plant on plants that have common pathogens), timely destruction of weeds during the growing season and in autumn of plant residues, high-quality digging of the site are required. Before sowing the varieties, if you got them yourself, soak them in a 1% solution of potassium permanganate (20-25 minutes). A special role is given to the correct application of mineral and organic fertilizers.

Before the onset of the initial symptoms of mycoses, the plants are fed with phosphorus-potassium fertilizers, which increase the resistance of the plants. A good effect for enhancing the immunity of a tomato is given at the very beginning of flowering by spraying it on the leaf surface with a superphosphate solution. To prepare it, take 50 g of fertilizer per 1 liter of boiling water and insist for a day. The resulting settled solution is drained (without shaking), after which the mother liquor is diluted with water (1: 9). Solution consumption is 1 l / 10 m? landings.

Reduces susceptibility to fungal diseases and improves the quality of the fruit, fertilizing plants with potassium fertilizers (for example, potassium sulfate -15 g / m2). For better ventilation of plants in greenhouses and hotbeds, after setting the fruits, the lower leaves are gradually removed on the first brush. In the fight against late blight, it is important to avoid excessive moisture, and if it is threatened, watering is reduced. When the first vague spots of this mycosis appear, diseased fruits are immediately removed. Some gardeners even remove diseased bushes, although this is already a belated event.

It is possible to slow down the process of tomato infection with fungal diseases (especially late blight) and save its plants by spraying them with biological and chemical preparations, solutions of which, after being applied to the foliage, prevent spores from germinating and protect it from infection. But, as a rule, fungicides cannot destroy the mycelium, which has already penetrated into the inner tissues of the foliage. Treatment of already infected plants can only slightly restrain the development of the disease. It is advisable to start the fight against late blight of tomato with the help of these drugs before the first signs of mycosis appear.

It is better to timely process tomato plants with the onset of the disease on potato bushes. Such preventive treatment can protect tomatoes for 2-2.5 weeks. The biological product Baksis (0.1 g / 5 l) is used in the open field against late blight and alternaria during the growing season (the first one is preventive, the next one - with an interval of 15 days at a working fluid flow rate of 5 l / 100 m?). Spraying with alirin-B (10 tablets / 10 l) during the beginning of budding-fruiting (with an interval of 10-14 days) gives a positive effect against late blight.

By treating plants in the open field (with an interval of 14 days) with a solution of the biofungicide gamair (10 tablets / 10 l) during the budding-fruiting period, the harmfulness of this disease is reduced. During the growing season against late blight and Alternaria, plants are sprayed with chemicals: ordan (in open ground 25 g / 5 l, in closed 25 g / 8 l), preventive treatment (stage 4-6 true leaves or no later than two days after tomato infection, subsequent ones - with an interval of 7-10 days, as well as abiga-peak (50 g / 10 l).

Tomato bacterial cancer

Tomato bacterial cancer is ubiquitous and highly harmful. Symptoms of this disease are typically of a vascular nature, usually in the form of wilting of plants. This process begins with the loss of turgor at the lower tiers of the leaves (even on one side of the leaf), the wilting parts of the leaf turn yellow at the edge and curl. Sometimes such a manifestation of bacteriosis is its only external symptom. From the beginning of wilting to the complete death of the plant, it can take up to 1.5-2 months. In primary infection, darkening of the vascular ring in the stems and at the base of the petioles of diseased leaves is noted.

Early damage to fruits by bacteriosis leads to their ugliness (seeds darken, lose germination). The defeat of the aboveground organs of fruiting plants is noted in the form of brown sores on young sepals, stems, petioles (especially on the stalks, which causes the fruit to fall off). With a later infection, the fruit may look healthy and have a normal pulp consistency. Signs of bacteriosis on fruits occasionally appear in the form of a spot, which is called the "bird's eye".

In this case, at the first stage, small affected areas of green fruits look like white spots, at the next stage, when the fruits ripen and become stained, the center of the spots turns yellow. The development of diseased fetuses is delayed, they are heterogeneously colored in comparison with healthy ones. The pathogen enters the plant through mechanically injured roots, leaves and stems (even breaking the hairs on the stem is enough).

At high air humidity, the pathogen can infect the plant through open stomata. Infection with bacterial tomato cancer is spread by plant debris, seedlings, soil, can come in with splashing water (during irrigation or rain), but the dominant role here belongs to infected seeds, infected superficially or from the inside (the infection persists in them for up to three years).

The pathogen is also transmitted by pinching and pruning of plant leaves. With a permanent tomato culture, the soil serves as a reservoir of bacterial infection. The most favorable conditions for the development of bacteriosis are temperatures of 20 … 28 ° C and relative humidity of 80-85%. During the rainy season in hot weather, the spread of the disease can take the form of an epiphytotic.

Black bacterial spot of tomato

Black bacterial spot of tomato is especially harmful in years with hot summers (damage to seedlings - up to 50%, and fruits - 20%). The harmfulness of bacteriosis is manifested in the defeat of the aerial part of the plants, as a result of which the plant does not yield fruits or they are of low quality. The disease affects the cotyledons, leaves, petioles, stems and fruits of tomato (young tissues are more susceptible to the pathogen than aging ones). Seedlings and young plants suffer greatly from bacteriosis.

First, on young leaves, very small depressed watery brown spots of irregular shape appear, they quickly increase in size (up to 1-2 mm), then the center of the spots gradually turns black. As the disease progresses, the spots merge, the leaves curl and dry out. On the stems, petioles, peduncles, shoots and pericarp, the disease causes the appearance of black elongated spots.

With a strong lesion of the peduncle, a massive fall of flowers occurs. When fruits are affected in the early phase, dark convex points surrounded by a watery border appear on their surface, which eventually take the form of ulcers. Unlike typical symptoms of bacterial bird's-eye cancer, dark scab-like spots are not surrounded by a light border.

The development of black spot is influenced by meteorological conditions: the lower the temperature, the slower the development of black spot. The bacteriosis is transmitted by seeds and plant debris. On seeds, the infection can persist for up to one and a half years. Even with a latent infection, seeds can give outwardly healthy seedlings, which in the future can serve as a source of spread of bacteriosis. For this reason, it is important to purchase guaranteed healthy seeds. The pathogen persists for a very long time in parts of plants that are difficult to rot.

Fight bacterial diseases of tomatoes

In the fight against bacteriosis, it is important to observe crop rotation (place tomatoes in one place for no more than two years, and after the first year it is necessary to remove a layer of soil 5-7 cm thick in the greenhouse). Although it is advisable to grow them for only one season. It is necessary to carefully destroy plant residues. It is important to use healthy seeds, when working with your own material - leave seeds only from healthy plants.

Varieties and hybrids resistant to bacterial cancer are absent; according to experts, the Siberian early ripening variety is characterized by relative immunity to it. Wreath, Molniya, Excellent, Potok, Juliana and Volzhsky, Kronos hybrids are considered relatively resistant varieties to black bacterial spot. Variety Compatriot and hybrid Gelena are resistant, and variety Balada is tolerant to Alternaria and black bacterial spot.

In order to prevent bacteriosis in the pre-sowing period, the seeds should be disinfected by heat treatment in hot water (48 … 50 ° C) for 15-20 minutes, and then cooled in cold water (3-4 minutes). Some gardeners successfully sterilize seeds in an aqueous solution of garlic pulp (1: 1) or in aloe juice for 6-8 hours (it should be noted that a solution of potassium permanganate does not work on bacteria). Against bacterial cancer, it is recommended to spill the soil with a suspension of hamair (2 tablets / 10 l) in greenhouses and hotbeds (1-3 days before sowing seeds).

To combat these bacterioses, experts recommend the biological product Fitosporin-M: pre-planting soaking of seeds (followed by drying) in a solution (3 ml / l) for 1-2 hours, and before planting in open ground, immersing the roots of seedlings for 1-2 hours in solution of the drug (3 ml / l) (at the rate of 1 l / 100-150 plants). Also, against black bacterial spot and late blight, plants are sprayed with a 0.1% solution of Fitosporin-M during the growing season (7-10 days after planting in the ground); subsequent processing - after 2-3 weeks (at a working fluid flow rate of 10 l / 100 m?).