What to do if yellow spots appear on tomato leaves: diagnose the cause and effectively combat it
Yellowing of tomato leaves may be a natural physiological process of the plant. For example, the normal reaction of seedlings to transplantation into a greenhouse or open ground. However, a change in the color of the tops often indicates the presence of problems: errors in agricultural technology, infection with various infections, or attack by pests. The seriousness of the situation should not be underestimated, since we are talking about the loss of the entire harvest.
Today we will tell you why yellow spots, and we will reveal methods of control and methods of prevention.
Diseases as the cause of yellow spots on tomato leaves
Not only people have a weakness for tomatoes, but also various pathogenic microorganisms that cause bacterial, viral and fungal plant diseases.
Septoria or white spot
The causative agent is a fungus from the class of deuteromycetes Septoria lycopersici Speg.
Symptoms of the disease:
- at the initial stage, watery spots 2-3 mm in size appear on old leaves;
- then the spots turn white and grow up to 5 mm in diameter;
- a dark rim forms around them, and in the center there are black-gray zones of accumulation of fungal spores (pycnidia).
Septoria It mainly affects leaves, less often – sepals, stems and fruits. As the disease develops, the spots merge into one, the shoots die and fall off. As a result, the development of the entire bush slows down, since all the energy and nutrients are spent not on the development of fruits, but on the formation of new leaves.
Reference. The disease is typical for tomatoes grown in open ground.
Promotes infection:
- hot weather;
- heavy rainfall;
- excessive watering.
Fungal spores actively multiply in moist soil, are spread by insects, are carried by wind, rain or drops of irrigation water, and can settle on work equipment and clothing.
Cladosporiosis, or brown, olive spot
The causative agent is the fungus Cladosporium fulvum Cooke, which is striking in its incredible vitality: it easily tolerates frost, drought, and can survive without a host plant for 10 months. Reproduces asexually, producing conidia - light, dust-like spores that spread quickly not only through working tools and water, but also through the air.
Reference. Unlike septoria, this fungal disease often affects plants grown indoors - in greenhouses and greenhouses.
Symptoms:
- yellowish spots on the upper part of the leaf blade, contrasting sharply against the background of green tops;
- a light coating forms on the back of the infected leaf, which later develops into brown spots;
- shoots become denser and velvety;
- Without timely measures to combat the disease, the leaves turn yellow, dry out and fall off.
The first signs of the disease usually appear at the stage of flowering and formation of the ovary of tomatoes. Cladosporiosis spreads from bottom to top, preventing normal nutrition of the plant and slowing down the ripening of fruits.
Factors in the development of infection are high humidity (90-95%) and temperature changes.
Mosaic
The causative agent is the Tomato mosaic tobamovirus virus. As a rule, planting seeds are infected. The virus can also spread through the soil (it can withstand high and low temperatures), from neighboring crops - potatoes, cucumbers. The disease is often transmitted by insects - ticks, aphids, beetles.
Symptoms:
- Multi-colored blotches form on the leaves;
- spots can be of various shapes and sizes, have a bright border;
- leaves stretch and curl;
- the fruits are struck by a “kaleidoscope” of light green and white spots;
- The tomato pulp begins to turn black and rot.
Conditions favorable for the disease are:
- heat;
- high humidity;
- lack of light;
- excess nitrogen in the soil.
Mosaic comes in several types: ordinary, tobacco (spots develop into bumps), green or white, depending on the color of the inclusions.
Chlorotic curl, or tobacco necrosis mosaic
The causative agent is the Tomato leaf curl virus.
Symptoms:
- the leaves lighten at the edges, in the center the color remains dark green;
- the upper shoots bend and curl, appearing curly;
- the growth and development of the bush is greatly slowed down;
- the green mass becomes smaller, the shoots are partially exposed;
- flowers fall;
- the ovaries harden and do not develop.
The disease is promoted by high humidity, and the virus spreads through:
- contaminated soil;
- infected seeds;
- pest – greenhouse whitefly.
Alternaria, or dry spotting
The causative agent is the fungus Alternaria solani Sorauer.
Symptoms:
- dry yellow spots of various sizes appear along the edge of the leaf;
- then they spread out and merge with each other;
- later, a black coating forms on the spots - accumulations of fungal spores;
- even after rain or watering, the stains remain dry.
Alternaria blight affects all vegetative organs of the plant: first the lower leaves, then the stems and fruits. The spots on the stems are gray-brown, oblong; on the fruits - dark brown, round, pressed inward. The pulp darkens and becomes unsuitable for food.
Attention! Tomatoes in glass greenhouses get Alternaria blight more often than under film or in open ground.
Promotes spore germination:
- temperature above +25°C;
- sudden changes in temperature;
- wetting the bush when the soil is insufficiently moistened (heavy dew, alternating rainy days and dry weather);
- poor ventilation and high humidity in the greenhouse.
Fusarium
The causative agent is fungi of the genus Fusarium.
The disease affects the plant's vascular system, clogging the channels and interfering with the circulation of nutrients. In addition, the death of shoots is associated with compounds that fungi release during their life processes.
Symptoms:
- leaves turn pale green or yellow, curl, and then fall off;
- the veins become discolored, the petioles are deformed;
- the top of the bush gradually fades;
- at high humidity, a white coating on the roots is clearly visible - fungal mycelium;
- When cut, the vessels have a dark brown color.
The danger of the disease lies in the fact that it is almost impossible to diagnose it before the period of flowering or fertilization of tomatoes.
Convenient to fusarium:
- dense plantings;
- proximity to groundwater;
- poor lighting and short daylight hours;
- drought, drying out of plant roots.
Agrotechnical errors and external factors
The appearance of yellow spots may indicate improper care of the plant. Most often this is due to over- or under-watering, lack of nutrients, harmful effects of sunlight, etc.
Improper watering
Frequent and shallow watering weakens the immunity of tomato bushes and makes them more susceptible to disease. They create excess moisture in the upper layers of the soil, but are not sufficient for normal plant nutrition.
Basic Rules:
- You need to water tomatoes rarely, once every 7-10 days, but regularly and generously;
- the optimal time for watering is morning, so that by evening the top layer of soil in the garden bed has time to dry;
- after 6-12 hours, it is advisable to loosen and mulch the soil;
- Water should not get on the leaves and stems of the tomato.
With insufficient water supply, the plant does not absorb calcium from the soil well, and dark brown dry spots form on the tops of the fruit - signs of blossom end rot.
Malnutrition
Changes in leaf color in tomatoes can be caused by an imbalance of micro- and macroelements in the soil:
- with nitrogen starvation, the leaves turn white or yellow (chlorosis), and the veins acquire a bluish-red tint;
- excess nitrogen leads to “fatification” of the bushes, necrosis of the leaves - they become covered with yellow or brown spots and then die;
- with a lack of phosphorus, tomato leaves become smaller and curly, the lower parts acquire a purple tint;
- with a lack of potassium, yellow-brown spots spread along the edges of the leaf, over time the entire plate turns yellow and turns inward;
- with sulfur deficiency, the upper leaves lighten, their veins turn red, the stems become thin, woody and brittle;
- that the plant lacks boron, indicates the curvature of the upper leaves - then they turn yellow or become light green, curl from the ends to the bases, the veins darken, acquire a dark brown or black color;
- iron deficiency is manifested by yellowing of the central part of young leaves, later the yellow color spreads and only the edges remain greenish;
- symptoms of manganese deficiency are similar to iron deficiency - yellow spots form between the veins, then the leaves dry out and fall off.
Ultraviolet burn
Too intense lighting can be detrimental to such a capricious plant as a tomato. In this case, yellow spots on the leaves are burns. Most often they form where water gets in after watering or where dew falls. The drops work like a magnifying glass, enhancing the effects of sunlight. Thermal damage to tissue is fraught with further necrosis.
Other reasons
Other factors leading to yellowing of the leaves of tomato bushes:
- poor lighting leads to yellowing of the lower leaves, where light penetrates the worst;
- problems with the root system - their damage due to careless planting of seedlings, loosening the soil, pulling out weeds;
- hypothermia;
- presence of pests – wireworms, mole crickets, aphids, spider mite.
Yellow spots on greenhouse tomatoes
In greenhouses, more often than in open ground, favorable conditions are created for the development of various diseases:
- waterlogged soil;
- increased air temperature;
- irregular ventilation.
In addition, spores of pathogenic fungi and other microorganisms can settle on structural elements.
Reasons for the appearance of spots on tomato leaves in open ground
The most common problems in open beds are:
- poor quality, contaminated soil;
- excess light and sunburn on the tops;
- prolonged rains and heavy dew;
- sudden changes in temperature.
How to identify the cause
First of all, a visual inspection of the plants is necessary.
Attention should be paid to the following details:
- which leaves are affected by spots - upper or lower;
- on which surface of the leaf plate there is plaque - upper or lower;
- Do the spots spread to other vegetative organs - stems, flowers, ovaries and fruits;
- vein condition;
- the presence of damaged vessels on the cut.
Then you should analyze the agricultural practices and conditions for growing tomatoes:
By comparing the symptoms of diseases and the consequences of violations of agricultural practices with the identified problems, we can judge the cause of yellowing of tomato leaves.
What to do
The first measures upon detection of any disease:
- isolation and subsequent destruction of the infected bush;
- treatment of other plants with special solutions.
Helps in the fight against disease:
- folk recipes - ash, soap solution, whey, iodine;
- broad-spectrum fungicides - “Fundazol”, “Ordan”, “Previkur”, “Bravo”, HOM, “Poliram”, etc.);
- biological agents – “Fitoflavin”, “Fitosporin”, “Pseudobacterin-2”, etc.
The lack of micro- and macroelements in the soil is compensated by regular fertilizing with complex mineral fertilizers.
Attention! To avoid poisoning, tomatoes from bushes treated with chemicals can be eaten no earlier than after 3 weeks. Unlike fungicides, substances of biological origin do not penetrate inside the fruit, but work exclusively on the surface, and therefore are considered safe for humans.
Preventive measures
Preventive measures will help prevent diseases and the harmful effects of the environment:
- thorough preparation of the site in the fall - digging up the soil, applying fertilizers;
- regular disinfection of greenhouse frames, equipment, work clothes;
- compliance with the rule of crop rotation - a break of 3-4 years before planting tomatoes in the same area;
- use of varieties and hybrids resistant to diseases;
- disinfection of seeds and planting soil - calcination, freezing, treatment with disinfectant solutions;
- timely destruction of weeds and remains of infected plants;
- regular ventilation of greenhouses and greenhouses;
- shading seedlings on hot, sunny days;
- control of humidity levels, optimal watering;
- loosening and mulching soil under bushes;
- timely application of mineral fertilizers and organic fertilizers.
Conclusion
Yellow spots on tomato tops cause serious concern to the gardener. In the case of natural aging and dying of leaves, these are vain fears. If the plants are infected or agricultural practices are disrupted, it is necessary to take timely and decisive action to preserve the harvest.