Diagnosis

Example #1: Leaf Yellowing (Chlorosis)

Yellowing is one of the most common and deceptive symptoms. It can indicate dozens of different problems:

• Nitrogen (N) deficiency: Old leaves begin to yellow evenly from the edges to the center, and plant growth slows down (Akhatov, 2010).
• Magnesium (Mg) deficiency: The tissue between the veins turns yellow (interveinal chlorosis), starting with older leaves. The veins remain green (Wien & Stützel, 2020).
• Iron (Fe) deficiency: Young leaves at the top of the plant turn yellow, while the veins remain bright green (reticulate chlorosis). This often occurs on alkaline soils (Blancard, 2012).
• Viral disease (e.g., Mosaic Virus): A mosaic pattern of yellow and green spots appears on the leaves (Blancard, 2012).
• Overwatering and root rot: Yellowing of leaves, often accompanied by wilting, even if the soil is moist (Cumble, 2022).
• Root damage by pests (nematodes): The plant turns yellow and wilts because the root system cannot supply it with water and nutrients (Akhatov, 2010).

As you can see, all these problems share the same external symptom, but the treatment will be completely different: in one case, you need to add nitrogen, in another — magnesium or iron, in a third — adjust watering, and in a fourth — remove the diseased plant and treat neighboring ones for viruses.

Example #2: Leaf Spots

Dark or brown spots on leaves can be a symptom of:

• Fungal disease (Alternaria, Phytophthora, Septoria): Spots usually have a characteristic structure (e.g., concentric rings) and are often surrounded by a yellow halo (Blancard, 2012).
• Bacterial disease (Bacterial Spot): Spots are oily, often angular, and restricted by veins (Blancard, 2012).
• Sunburn: Spots appear on the most exposed areas of the leaf or fruit, looking pale and bleached (Blancard, 2012).
• Phytotoxicity (chemical burn): Spots appear unevenly, in places where droplets of fertilizer or pesticide solution accumulated during spraying (Akhatov, 2010).

Treatment will differ drastically. Fungicides are needed for fungi, bactericides for bacteria, and nothing can be done about sunburn except to provide shade.

Main takeaway: One symptom can have many causes. "Eyeballing" and "guessing" a diagnosis is the shortest path to losing your harvest and becoming discouraged. To start acting correctly, you need to stop being a passive observer and become a detective. The following chapters of our article will teach you an investigative methodology that helps accurately determine the cause of the problem.

2.1. Lower, Old Leaves

If the problem starts on the lower, mature leaves and gradually moves upward, it almost always indicates issues with mobile nutrients or long-term stress.

Deficiency of mobile nutrients (N, P, K, Mg): The plant, like a smart manager, transfers valuable nutrients from old leaves to young ones and fruits where they are needed most. Therefore, the lower leaves suffer first (Wien & Stützel, 2020; Akhatov, 2010).

• Nitrogen (N): Old leaves become uniformly pale green or yellow.
• Potassium (K): Edges and tips of old leaves turn yellow and dry out (marginal burn).
• Magnesium (Mg): Tissue between the veins on old leaves turns yellow, while the veins remain green (interveinal chlorosis).

Natural Aging: This is a normal process. If the lower leaves gradually yellow and die off, and the plant looks generally healthy, there is no need to worry.

Fungal Diseases (Alternaria, Septoria): Many fungi start their "attack" from the lower leaves, which are closer to the ground and remain wet longer (Blancard, 2012).

Root Problems: If roots are damaged, the lower leaves are the first to suffer, as it is hardest to deliver water and nutrients to them. The plant starts wilting from the bottom up (Cumble, 2022).

2.2. Upper, Young Leaves and the Growing Point

If the problem appears at the top of the plant, where the youngest leaves are, it indicates an issue with immobile nutrients or a rapidly spreading infection.

Deficiency of immobile nutrients (Fe, Ca, B, Zn, Cu, Mn, Mo): These elements get "stuck" in older plant parts and cannot be redistributed to young shoots where they are needed for growth (Wien & Stützel, 2020; Akhatov, 2010).

• Iron (Fe): Young leaves turn yellow while veins remain green (reticulate chlorosis).
• Calcium (Ca): Young leaves grow deformed, and the growing point dies off. This often leads to blossom end rot in fruits.
• Boron (B): Growing point dies off, young leaves become brittle and deformed.

Viruses: Many viruses (Mosaic Virus, Tomato Yellow Leaf Curl Virus) attack young, actively growing tissue. Leaves at the top may become small, wrinkled, curled, or show mosaic coloring (Blancard, 2012; Gavrish, 2005).

Abiotic Stress (sunburn, herbicide damage): The most delicate, young parts of the plant suffer first.

2.3. Stem

• Darkening or corking at the stem base: Often indicates Fusarium or Verticillium wilt, as well as stem Phytophthora (Blancard, 2012).
• Cracks and wounds on the stem: Can be mechanical damage, result of improper staking, or activity of stem borers.
• Thickening and appearance of aerial roots on the stem: Often a sign of stress due to overwatering or lack of oxygen at the roots (Akhatov, 2010). The plant tries to "breathe" through the stem.

2.4. Fruits

Fruit problems are always the "cherry on top." They signal that the problem is already serious and affects the entire organism.

• Blossom End Rot (black spot on the fruit tip): This is not an infection, but a physiological disorder caused by an acute calcium (Ca) deficiency during the period of active fruit growth. The cause is often irregular watering or high salt concentrations in the soil (Wien & Stützel, 2020; Akhatov, 2010).
• White or yellow uneven coloring ("green shoulders"): A symptom related to potassium deficiency or exposure of fruits to direct sunlight (Blancard, 2012; Cumble, 2022).
• Spots, rot, holes in fruits: This is the direct work of pathogens (fungi, bacteria) or pests (caterpillars, fruitworms, thrips) (Blancard, 2012).

2.5. Roots (Don't Ignore Them!)

The root system is the "underground kingdom," and without examining it, a diagnosis will never be complete. If leaves are wilting but the soil is moist, you must check the roots immediately (Akhatov, 2010).

Healthy roots: White or light yellow, firm, with many small rootlets.

Diseased roots:

• Brown, soft, disintegrating: A clear sign of root rot caused by fungi (Pythium, Phytophthora) or bacteria. This often happens due to overwatering (Cumble, 2022; Blancard, 2012).
• Swelling (galls) on roots: Infestation by root-knot nematodes. These microscopic worms make the roots unable to absorb water and nutrients (Akhatov, 2010; Blancard, 2012).
• Brown or black vessels on the root cross-section: A typical sign of vascular diseases — Fusarium and Verticillium wilt. Fungal spores clog the conducting pathways inside the plant (Blancard, 2012).

Main idea of this section:

Diagnosis is like a detective investigation. The first question you should ask yourself when you see a problem is: "Where exactly is this happening? " The answer to this question will eliminate half of all possible causes and point you in the right direction.

In the next chapter, we will learn to analyze the symptoms themselves: what exactly changed — color, shape, structure?

3.1. Chlorosis (Yellowing of Tissues)

Chlorosis is not a disease but a symptom indicating a disruption in chlorophyll production. It can be caused by nutrient deficiency, viruses, root damage, or stress (Blancard, 2012; Akhatov, 2010).

Uniform chlorosis (all leaves pale evenly):

• Most often — Nitrogen (N) deficiency. The plant is "starving," and the whole leaf becomes pale green or yellow (Wien & Stützel, 2020). Especially noticeable on older leaves.
• Can also be a result of Sulfur (S) deficiency, which shows on young leaves.

Interveinal chlorosis (veins green, tissue between them yellow):

• On old leaves — this is a classic sign of Magnesium (Mg) deficiency (Wien & Stützel, 2020; Akhatov, 2010).
• On young leaves — Iron (Fe) or Manganese (Mn) deficiency. This often occurs on alkaline soils where iron and manganese are "locked" and unavailable to the plant (Blancard, 2012).

"Golden" or "orange" mottling (uneven chlorosis):

• This could be a viral disease (e.g., Mosaic Virus, Tomato Spotted Wilt Virus). Leaves are covered with a mosaic pattern of light and dark spots (Blancard, 2012).
• Can also be a sign of Zinc (Zn) or Copper (Cu) deficiency.

3.2. Necrosis (Tissue Death)

Necrosis is cell death visible as dry, dark spots. Necrosis is the final outcome of any damage, whether from disease, burn, or starvation.

Dry, brown, "papery" necrosis:

• Marginal necrosis (leaf edges dry up): Often linked to Potassium (K) deficiency (Wien & Stützel, 2020).
• Interveinal necrosis (areas between veins dry up): In severe magnesium deficiency, but can also be a symptom of Alternaria and other fungal diseases (Blancard, 2012).
• Punctate necrosis (tiny dead spots): Can be caused by Bacterial Spot, Sunburn, or Chemical burn (from fertilizers or pesticides) (Akhatov, 2010).

"Wet," dark, rotting necrosis:

• This is a sign of an aggressive infection, most often fungal (Phytophthora, Gray Mold) or bacterial (Soft Rot). Tissues soften, become slimy, and emit an unpleasant odor (Blancard, 2012).

Concentric necrosis (spots "like a target"):

• A classic symptom of Alternaria ("Early Blight"). Spots are brown with characteristic "rings" of different shades (Blancard, 2012).

Necrosis with a "beak" (V-shaped):

• Often encountered in Bacterial Canker of tomato — a disease affecting the vessels. Leaves wilt and dry from one edge, taking the shape of an inverted V (Blancard, 2012).

3.3. Leaf Curling and Deformation

Leaves can change shape. This is one of the most informative symptoms.

Leaf curling upward ("boat-shaped"):

• Often physiological — the plant's reaction to heat, drought, or sudden weather changes. This is a protective response to reduce evaporation (Blancard, 2012). Usually not related to disease.
• Can be a sign of Potassium (K) or Phosphorus (P) deficiency.

Leaf curling downward ("claw-like"):

• Often indicates overwatering (root waterlogging) or root damage.
• With herbicide damage (especially from 2,4-D), leaves become severely deformed and curl downward (Blancard, 2012; Akhatov, 2010).

Leaf deformation (thickening, curling, "fern-like"):

• A serious sign of viral infection (Mosaic Virus, Aspermy). Young leaves become thread-like (phyllody) or asymmetrical (Blancard, 2012; Gavrish, 2005).
• Deformation accompanied by yellowing is characteristic of Boron (B) or Calcium (Ca) deficiency.

3.4. Wilting

Wilting is a loss of turgor. Leaves and stems become limp and droop.

Temporary wilting during hot hours (recovers by evening):

• A normal reaction to extreme heat or lack of moisture in the air. Watering and mulching will help.

Permanent wilting despite moist soil:

• The most dangerous signal! This almost always means the plant cannot get water through its roots. Causes:
• Root damage (rot, nematodes, overwatering) (Akhatov, 2010; Cumble, 2022).
• Vascular diseases (Fusarium, Verticillium, Bacterial Wilt) — fungi or bacteria clog the conducting vessels in the stem, preventing water from reaching the leaves (Blancard, 2012). When cutting the stem of such a plant, you will see darkened vessels.

3.5. Growth Stunting

The plant seems to "freeze." Internodes become short, new leaves are small.

• Nutrient deficiency (especially phosphorus): Plant stops growing, stems and leaves become purple or dark green (Akhatov, 2010).
• Low temperature: Tomato growth stops below +10°C (Wien & Stützel, 2020).
• Viral infection: Many viruses (e.g., Tomato Yellow Leaf Curl Virus) "stop" the plant, making it dwarfed (Blancard, 2012).

Main idea:

We are learning to see not just "yellow leaves" but a specific subtype of symptom. Right now, try it. Find any symptom on your plant and describe it using these categories.

The next step is to search for "living clues" — what remains after the work of pests and pathogens. More on this in Chapter 4.

4.1. Look: Examine with the Naked Eye and a Magnifying Glass

A magnifying glass (10x or 20x magnification) is a diagnostician gardener's best friend. Many pests and pathogen structures are microscopic and invisible without magnification.

Fungal growths and sporulation:

• White powdery coating on the upper leaf surface: Fungal disease Powdery Mildew. Mycelium and spores cover the leaf like flour (Blancard, 2012).
• Olive-brown velvety coating on the lower leaf surface: This is Cladosporiosis (Leaf Mold). Especially common in greenhouses with high humidity (Blancard, 2012; Akhatov, 2010).
• White "fluffy" mold: Appears on fruits or stems with Gray Mold (Botrytis) or Sclerotinia (Blancard, 2012).
• Sporulation as black dots: On old leaves or stems, black dots may form — these are fungal pycnidia (Septoria, Phoma) or sclerotia (Blancard, 2012). These are like the fungus's "seeds" left for infection next year.

Insects and their waste products:

• Aphid colonies: Usually on the underside of leaves and young shoots. Visible to the naked eye (Blancard, 2012; Akhatov, 2010).
• Webbing: Presence of fine webs on leaves indicates Spider Mite activity. The mite itself is very small, but the web is easily visible (Blancard, 2012).
• Insect eggs: Egg clusters are often noticeable on the underside of leaves. Eggs of fruitworms, whiteflies, and bugs have characteristic shapes and colors.
• "Mines" and tunnels: Winding light-colored trails inside the leaf are the result of Leaf Miner activity (larvae of certain flies). They "eat" the leaf tissue from the inside (Blancard, 2012).
• Feces (frass): Black or dark pellets, drops, or streaks on leaves and fruits are insect waste from caterpillars, beetles, or aphids (Blancard, 2012).
• Necrosis and puncture marks: Tiny light dots or spots can be feeding puncture marks from insects (thrips, bugs, leafhoppers) (Akhatov, 2010).

Pest traces on roots:

• Galls (swellings): Rounded swellings on roots are nematode galls, inside which live microscopic worms (Akhatov, 2010; Blancard, 2012).
• Tunnels and damage: Larvae of click beetles (wireworms), mole crickets, and other soil pests can gnaw roots and stems at the base.

4.2. Touch: Assess Tissue Consistency

What we see is important, but what we feel can sometimes tell us more.

Soft, watery tissues:

• If a leaf or fruit feels soft and "wet," this is a sign of wet rot (bacterial or fungal, like Phytophthora). Tissues are decomposing and losing structure (Blancard, 2012; Cumble, 2022).

Dry, brittle tissues:

• Leaves or stems become brittle and break easily. This could be a result of potassium deficiency (edges drying), Alternaria (spots becoming dry), or sunburn (Blancard, 2012).

Sticky, slimy exudates:

• If you notice slimy, sticky exudates on the stem or fruit, this often indicates a bacterial infection (Bacterial Canker, Bacterial Wilt) (Blancard, 2012).

Change in bark structure:

• If the stem bark easily separates from the inner part, revealing darkened vessels underneath — this is a sign of Fusarium or Verticillium wilt (Blancard, 2012; Akhatov, 2010).

4.3. Smell: Trust Your Nose

Smell is a chemical signal that can point to a specific type of problem.

Moldy, musty smell:

• Characteristic of many fungal rots, especially when they develop in high humidity conditions.

Putrid, unpleasant smell (smell of decomposition):

• This is almost always a sign of "wet" bacterial rot (e.g., Erwinia or Pseudomonas). Bacteria decompose tissues, releasing foul-smelling gases (Blancard, 2012).

Sour smell:

• May occur with Sour Rot, caused by some yeast-like fungi (e.g., Geotrichum candidum) (Blancard, 2012).

Sweetish, cloying smell:

• Sometimes characteristic of damage by certain pests (e.g., aphids) or fungi that secrete sugary exudates.

Main idea of this section:

You stop being just an observer and become an investigator. You don't just see a "spot," you see fungal "sporulation" under a magnifying glass. You don't just feel that a leaf "has rotted," you feel wet rot that smells, distinguishing it from dry necrosis.

This comprehensive approach — "look, touch, smell" — allows you to separate infectious diseases from physiological disorders and pest damage.

In the next chapter, we will piece all the evidence together and learn to ask the right questions about recent events.

5.1. Weather: Was there an anomaly?

Tomato is a crop very sensitive to weather fluctuations. A sudden change in weather is one of the main stress factors (Wien & Stützel, 2020).

Was there extreme heat (above +32°C)?

• What happens: At high temperatures, tomato pollen becomes sterile, and flowers drop without setting fruit. Leaves may curl upward ("boat-shaped") to reduce evaporation (Blancard, 2012). This is a natural protective reaction, not a disease.
• What to do: Shading (shade netting), increased watering, spraying leaves with water in the morning. If flowers have already dropped, the yield on that truss is lost, but new trusses may set when temperatures normalize.

Was there a sudden cold snap (nights below +12°C)?

• What happens: Tomato growth stops, leaves may take on a purple hue (due to poor phosphorus uptake) (Akhatov, 2010). With prolonged cooling (below +10°C), wilting begins.
• What to do: Cover at night (spunbond, film) if it's a short-term phenomenon. If cold spells are prolonged, yields will decrease. Tomatoes are tropical plants; they don't like cold (Wien & Stützel, 2020).

Were there strong winds or hail?

• What happens: Mechanical damage to leaves and stems. Torn wounds appear, becoming "gateways" for infection. Leaves may be battered, as if shot with pellets (Blancard, 2012).
• What to do: First and foremost, preventive treatment with copper-containing products (e.g., Bordeaux mixture) to protect wounds from bacteria and fungi.

5.2. Watering: When and how did you water?

Watering is something we control, but often get wrong. Watering mistakes are a major cause of problems (Cumble, 2022).

Overwatering (soil constantly wet):

• What happens: Roots suffocate without oxygen (root asphyxia), begin to rot. The plant wilts even if the soil is moist. Lower leaves turn yellow and drop. Green algae or mold may appear on the soil surface (Akhatov, 2010).
• What to do: IMMEDIATELY stop watering! Let the soil dry out. Loosen the soil surface to improve aeration. If the plant is in a pot — repot it, removing rotten roots.

Underwatering (soil dried out):

• What happens: Leaves lose turgor (become limp), lower leaves may turn yellow and drop. Fruits become small and may crack at the first heavy watering (Wien & Stützel, 2020).
• What to do: Normalize watering. Water deeply but not frequently, so water penetrates deep to the roots. Mulching helps retain moisture.

Sudden change in watering regime:

• What happens: After a long drought, heavy watering leads to fruit cracking (Wien & Stützel, 2020; Akhatov, 2010). This is a physiological disorder, not a disease.
• What to do: Water evenly, avoid drying out and sharp fluctuations in moisture.

5.3. Fertilization: What and when did you feed?

Nutrition mistakes are a classic cause of problems. "Wanted the best, got the usual."

Did you apply fresh manure or poultry droppings?

• What happens: This is a common cause of root burn and excess nitrogen. Leaves become dark green, "fat," start curling, and fruits set poorly. The plant "luxuriates" (Akhatov, 2010).
• What to do: Use only well-rotted manure or compost. If you overfed, water the soil abundantly to wash out excess nitrogen.

Did you overdo mineral fertilizers?

• What happens: Excess salts (especially potassium and calcium) cause physiological drought — roots cannot absorb water. Leaves wilt, edges dry (marginal necrosis), blossom end rot of fruits may appear (Blancard, 2012; Akhatov, 2010).
• What to do: Stop fertilizing. Water the soil abundantly (leaching) and let it dry.

Micronutrient deficiency (e.g., boron):

• What happens: Growing point dies, young leaves deform, fruits become malformed (Akhatov, 2010; Blancard, 2012).
• What to do: Apply foliar feeding with a complete micronutrient fertilizer (e.g., "Master," "Kemira") or a specialized boron fertilizer.

5.4. Transplanting: How long ago and how?

Transplanting is always stress. If you transplanted seedlings into open ground or a greenhouse 1-2 weeks ago and their lower leaves started yellowing, this is often adaptation stress.

• What happens: The plant is establishing itself in a new location; its roots are actively growing but cannot yet fully support the above-ground part. Old leaves begin to die off, giving nutrients to the young ones (Akhatov, 2010).
• What to do: If the plant looks healthy, simply remove the yellowed lower leaves. Do not overwater or feed the plant in the first weeks. It will recover on its own.

5.5. Chemical Treatments: What and when did you spray?

Chemicals are powerful weapons, but if misused, they can cause burns (phytotoxicity) (Blancard, 2012; Akhatov, 2010).

What happens:

• High concentration of the product: Leaves are covered with brown or yellow spots (burn). This is especially noticeable on young leaves.
• Spraying in hot, sunny weather: Droplets of the solution act like lenses, concentrating sunlight and causing burns.
• Spraying herbicides near the planting: Tomatoes are very sensitive to herbicides (especially 2,4-D). Leaves become curled, deformed, as if "twisted" (Blancard, 2012). This is not treatable! You can only remove damaged parts or the whole plant.

What to do: Always strictly follow the dosage and instructions. Spray in the morning or evening, in calm weather. If you notice burns — stop treatments and let the plant recover. Herbicide damage cannot be cured; the plant must be removed.

Main idea of this section:

You are not just a diagnostician, you are an investigator. You don't just look at symptoms, you reconstruct the chain of events: "It was hot, then I watered heavily, and the next day I saw wilting." By linking symptoms to events, you can determine the cause with high probability.

Now that we have a complete picture — localization, symptom type, "living clues," and history — we are ready for the final stage: checking the environment and roots, which will provide the definitive answer.

6.1. Air Humidity

Humidity is one of the most powerful factors affecting tomato health. Tomatoes originate from the tropics; they like humidity, but not the kind we have in greenhouses or after rains (Akhatov, 2010).

What is considered normal: Optimal relative humidity for tomatoes is 60–70% (Cumble, 2022). This is the "sweet spot" where pollen doesn't stick together and pollination occurs normally, while fungal diseases don't develop.

High humidity (above 80%) — ideal conditions for diseases:

• What happens: Condensation ("dew") forms on leaves and fruits, providing an ideal environment for fungal spore germination (Phytophthora, Alternaria, Gray Mold) and bacterial multiplication (Blancard, 2012). Pollen becomes sticky, pollination worsens.
• How to check: Constant fogging of greenhouse walls, water droplets on leaves, morning mist. If the air feels humid and stuffy — it's bad.
• What to do: Ventilate the greenhouse! Tomatoes are not afraid of drafts (Akhatov, 2010). In open ground, the problem is solved by choosing a location with good air circulation. In greenhouses, use ventilation, shading, and avoid watering over leaves.

Low humidity (below 50%) — dry air:

• What happens: Pollen dries out, becomes sterile, and flowers drop. Leaves may curl to reduce evaporation (Blancard, 2012). This is especially relevant in hot weather.
• How to check: Dry air, especially on hot days when you feel thirsty. Dust on leaves dries quickly.
• What to do: Humidify the air (spraying paths in the greenhouse, mulching soil, placing water containers). But don't overdo it — dry air is still better for disease prevention than humid air.

6.2. Temperature

Temperature is the second most important factor after humidity. Tomato is a heat-loving crop with its own "preferences" (Wien & Stützel, 2020).

Optimal range:

• Day: 20–25°C.
• Night: 16–18°C. Night temperature should be at least 5°C lower than daytime. This is important so that carbohydrates accumulated during the day are not consumed at night by respiration (Wien & Stützel, 2020).

Heat (above +32°C):

• What happens: Pollen becomes sterile, flowers drop (fruits don't set). Leaves curl upward ("boat-shaped") — a protective reaction (Blancard, 2012). Growth slows, fruits may get sunburn.
• What to do: Shading (netting, whitewashing greenhouse), increased watering without overwatering. In greenhouses — ventilation and air humidification.

Cold (below +15°C day and +10°C night):

• What happens: Growth slows, pollen doesn't mature, leaves may turn purple (due to poor phosphorus uptake). Prolonged cold can kill the plant (Wien & Stützel, 2020; Akhatov, 2010).
• What to do: Cover at night, supplemental heating in greenhouses. If cold spells are prolonged, yields will be reduced.

6.3. Soil: pH and Structure

Soil is the home where roots live. It's important that the home is cozy.

Acidity (pH):

1. Optimal pH for tomatoes: 6.0–6.5 (slightly acidic) (Cumble, 2022). This is the ideal level for the uptake of all nutrients.

2. Acidic soil (pH < 5.5):

• What happens: Many micronutrients (iron, manganese, aluminum) become overly available and can cause toxicity. Phosphorus becomes "locked" and unavailable. Leaves may yellow (chlorosis), stems may turn purple (phosphorus deficiency) (Akhatov, 2010).

3. Alkaline soil (pH > 7.0):

• What happens: Iron, manganese, zinc, and boron become unavailable to the plant. This leads to yellowing of young leaves (chlorosis) and deformation (boron deficiency) (Blancard, 2012; Wien & Stützel, 2020).

4. How to check: The best way is to buy a pH meter or soil test strips. They are inexpensive and very informative.

5. What to do:

• To raise pH (acidic soil): Add dolomite lime (contains magnesium and calcium) or agricultural lime several weeks before planting (Cumble, 2022). This provides a slow but lasting effect.
• To lower pH (alkaline soil): Add sulfur, aluminum sulfate, or use acidic fertilizers (ammonium nitrate, ammonium sulfate). But this process is more complex and slower.

Electrical Conductivity (EC):

1. What is it: EC is a measure of salt concentration in the soil solution. Simply put, it's soil "salinity." Especially important with drip irrigation and hydroponics.

2. High EC (salinization):

• What happens: The plant cannot absorb water, even if the soil is moist (physiological drought). Leaves wilt, edges dry, blossom end rot appears (Blancard, 2012).
• Causes: Over-fertilization, use of hard water, poor drainage.
• How to check: You need an EC meter (conductivity meter). This is a more advanced tool for experienced gardeners.
• What to do: Leach the soil with plenty of water (if there is drainage). In greenhouses — use quality water and strictly control fertilizer doses (Cumble, 2022).

Soil Structure:

1. What it should be: Loose, breathable, moisture-retentive. Tomatoes do not like heavy clay soils where water stagnates (Akhatov, 2010).

2. Soil compaction (crust):

• What happens: Roots suffocate from lack of oxygen, grow slowly, become vulnerable to rots. The plant wilts.
• What to do: Loosen soil after watering, mulch, add organic matter (compost, humus) to improve structure. In greenhouses — use drip irrigation and mulching film to avoid compaction.

Main idea of this section:

Environment is the foundation of plant health. You can treat any disease or fill nutrient deficiencies, but if environmental conditions (humidity, temperature, pH, salinization) are wrong, all your efforts may be in vain.

Checking the environment is not difficult but requires attention and some tools (pH meter, EC meter, thermometer, hygrometer). It's your insurance against many mistakes.

Now we are ready for the most powerful but often ignored step — checking the roots. More on this in Chapter 7.

7.1. How to Properly Inspect Roots

1. Dig carefully: Take one or two of the weakest or most problematic plants from different parts of the bed. Carefully dig them up with a large soil clod to avoid damaging roots.

2. Wash the roots: Gently wash the roots free of soil in a bucket of water, trying not to break the fine rootlets. This allows you to see all details (Akhatov, 2010; Blancard, 2012).

3. Examine: Place the roots on a flat, light-colored surface (board, paper) and inspect them carefully under good light, preferably with a magnifying glass.

4. Make a cut: Take a knife and make longitudinal and cross-sections of the main root and several lateral roots. This is important for examining the vessels (Blancard, 2012).

7.2. Healthy Roots: The Benchmark for Comparison

A healthy root is white, cream, or light yellow, firm, and succulent. It has many fine rootlets and root hairs that ensure water and nutrient uptake. On the cut, a healthy root has uniform light coloration without darkening (Akhatov, 2010; Blancard, 2012).

7.3. What You Might See: Key Signs of Root Problems

Here are the most common "distress signals" you can find when inspecting roots.

A. Brown, Soft, "Rotten" Roots

What they look like: Roots are not white but brown, tan, or even black. They have become soft, watery, and easily fall apart in your hands. The root cap and fine rootlets are almost absent. Sometimes an unpleasant putrid smell emanates from the roots (Blancard, 2012; Cumble, 2022).

What it indicates: This is root rot — damage to roots by pathogenic fungi (e.g., Pythium, Phytophthora, Rhizoctonia) or bacteria.

• Cause #1: OVERWATERING. Constantly wet soil deprives roots of oxygen. They weaken, and pathogens actively develop on them (Akhatov, 2010). Water displaces air from the soil, and roots begin to "suffocate" (root asphyxia). This is the most common mistake of beginner gardeners.
• Cause #2: COLD SOIL. At soil temperatures below +15°C, roots barely function, becoming vulnerable to rot (Wien & Stützel, 2020).
• Secondary symptoms on leaves: The plant wilts even if the soil is moist. Leaves turn yellow, starting from the bottom, and may drop. Growth is stunted (Blancard, 2012).

What to do:

• IMMEDIATELY stop watering! Let the soil dry out.
• If the plant is in a pot — repot it into new dry soil, after removing all rotten, black roots and treating the cuts with charcoal.
• In open ground — improve drainage, loosen the soil. In greenhouses — revise the watering regime, use drip irrigation, avoid water stagnation.
• In advanced cases — use biological products with Trichoderma (e.g., "Trichoderma viride") or chemical fungicides (copper-based), but they work better in early stages.

B. Swellings (Galls) on Roots

What they look like: Round or irregular thickenings, swellings, or nodules — galls — appear on thin and thick roots. They can be white, yellow, or brown (Akhatov, 2010; Blancard, 2012).

What it indicates: This is Root-Knot Nematode (Meloidogyne spp.) — a microscopic worm that parasitizes roots. The nematode penetrates the root and causes cell proliferation, forming galls. Inside the galls, nematodes live and reproduce (Blancard, 2012).

Secondary symptoms on leaves: The plant lags in growth, turns yellow, wilts, especially in hot weather. Externally resembles nutrient deficiency, but fertilizing doesn't help. Galls disrupt water and nutrient transport.

What to do:

• Prevention is key: Crop rotation (return tomatoes to this spot no earlier than in 3-4 years), planting resistant varieties (labeled "N" — nematode-resistant) (Cumble, 2022).
• Treatment: In open ground, infected plants cannot be cured. They must be removed and burned. Soil can be treated with biological products (e.g., based on fungus Paecilomyces lilacinus), but this is difficult and not always effective. The best methods are crop rotation and using resistant varieties. In greenhouses — replace the soil or deep treat it.

C. Darkened Vessels on Root (and Stem) Cross-Section

What they look like: On the cross-section of the main root or stem, just under the bark, you see a ring or individual spots of brown, dark brown, or almost black color. These are darkened conducting vessels (xylem) (Blancard, 2012; Akhatov, 2010).

What it indicates: These are vascular diseases (Fusarium wilt, Verticillium wilt, Bacterial wilt). Fungi or bacteria penetrate the vessels, clog them, and release toxins. Water and nutrients don't reach the leaves (Blancard, 2012).

Secondary symptoms on leaves: Very characteristic wilting — first, individual leaves or leaf lobes on one side wilt (one-sided wilting). In Fusarium, wilting often starts with lower leaves; in Verticillium, with upper ones. Then the whole plant wilts. On the stem cross-section just above the soil line, characteristic vessel darkening is visible. Fusarium is often accompanied by a pinkish growth at the stem base (Blancard, 2012).

What to do:

• The disease is incurable. Remove and burn affected plants immediately to prevent the infection from spreading.
• Prevention: Use resistant varieties (labeled "F" — Fusarium, "V" — Verticillium) (Cumble, 2022). Strict crop rotation (do not return tomatoes and other nightshades to this spot for 4-5 years). Disinfect soil and seeds.

D. Dry, "Corky" Roots with Cracks

What they look like: Roots are not rotten but have become hard, "woody," brown, with cracks resembling tree bark. Fine rootlets are practically absent (Blancard, 2012).

What it indicates: Often a sign of Pyrenochaeta root rot ("corky root rot"), caused by fungus Pyrenochaeta lycopersici. The disease is common in heavy, poorly drained soils (Blancard, 2012; Akhatov, 2010).

Secondary symptoms on leaves: Plant lags in growth, leaves become smaller, yellow (especially lower ones). Wilting occurs during hot hours, but turgor recovers at night. Yield drops sharply.

What to do: Prevention — crop rotation, improving soil structure (adding organic matter, sand), maintaining optimal moisture (without overwatering). Treatment is complex, often involving soil disinfection or biological products.

Main idea of this section:

Checking roots is the most informative but most frequently skipped step. If you see wilting or chlorosis, and fertilizing doesn't help, immediately check the roots. This simple procedure will allow you to distinguish:

• Nutrient problems (need to feed) from root rot (need to stop watering).
• Root diseases (need to treat soil or remove plant) from pests (need to use nematicides or change crop rotation).

Now that we have a complete picture — localization, symptom types, "living clues," history, environmental assessment, and root inspection — we are ready for the final stage: the table "what it could be." In the next chapter, we will bring all knowledge together and present a convenient key table for quick diagnosis.

Conclusion

We have traveled the full path from observation to accurate diagnosis. You have learned not just to "treat spots" but to understand your plant's language, to read the signals it sends. This knowledge transforms gardening from a struggle against the unknown into a conscious, fascinating, and, most importantly, effective activity.

Remember the main thing: a healthy plant is not one that never gets sick, but one that receives the right help in time. Use this article as a reference guide, and your harvest will reward you year after year.