Diagnostics

2.1. Seedlings (from emergence to transplanting)

This is the most critical and vulnerable stage. The main problems here are related to growing conditions.

Typical symptoms and causes:

• Damping off and rotting of the stem base ("blackleg"). The stem at the root collar darkens, thins, and rots. Plants are easily pulled from the soil. Cause: waterlogged soil, overly dense sowing, poor ventilation, sharp temperature fluctuations (Startsev, 2021). The solution lies in agricultural practices, not in treating already sick plants.
• Elongation and paleness. Seedlings are pale, with a long and thin stem. Cause: insufficient light or too high a temperature.
• Yellowing of cotyledons or the first true leaves. This is often related to nutrient deficiency in the small volume of soil or the onset of fungal diseases (e.g., downy mildew). A whitish coating may appear on the underside of the leaf (Welbaum, 2015).
• Growth stagnation. If the seedlings have "frozen" and are not developing, this could indicate low soil temperature, lack of moisture, or damage to the root system by pests (e.g., cabbage root fly larvae) (Pantyelyev, 1986).

Practical advice: At the seedling stage, almost all problems are related to overwatering, lack of light, and overcrowding. Carefully inspect the root collar and the underside of the leaves.

2.2. After transplanting to open ground (establishment period)

This is the most stressful period for the plant. At this time, it is extremely vulnerable to soil pests and infections.

Typical symptoms and causes:

• Wilting even with sufficient moisture. The plant looks limp despite moist soil. Cause: root damage during planting, or pest activity: cabbage root fly larvae or mole crickets gnawing on roots (Startsev, 2021). Another possibility is infection with Phoma or vascular bacteriosis, where the plant's vessels become blocked, and it cannot take up water even if it's available in the soil (Kemble, 2022).
• Damage to the apical bud ("heart"). If the central growing point is damaged, the plant may start forming several small heads instead of one large one. This can result from flea beetle activity (eating the growing point) or cabbage gall midge larvae (Startsev, 2021).
• Chewed edges and holes in leaves. At this time, flea beetles and diamondback moth caterpillars are particularly active and can completely destroy young plants (Nonnecke, 1989).

Practical advice: In the first 1–2 weeks after transplanting, carefully inspect the root collar and the growing point. If you detect wilting, gently dig around the root to check for fly larvae or other pests.

2.3. Active leaf growth (rosette stage)

At this stage, the plant is building its green mass. Signs of nutrient deficiencies and damage from leaf-chewing pests become clearly visible.

Typical symptoms and causes:

• Uniform yellowing of old lower leaves. This is a classic sign of nitrogen deficiency. The plant "translocates" nutrients from old leaves to young ones. If no action is taken, growth will slow down (Kemble, 2022).
• Yellowing of leaf edges ("marginal burn"). Most often indicates potassium deficiency. It can also be related to drought (Welbaum, 2015).
• Mosaic coloration and wrinkling of leaves. These are signs of viral diseases (e.g., cauliflower mosaic virus). They are transmitted by aphids and other sap-sucking insects (Startsev, 2021).
• Appearance of small holes ("shot-hole"). This results from flea beetle activity. On mature plants, they are less dangerous than on seedlings but reduce photosynthesis (Nonnecke, 1989).

Practical advice: At the active growth stage, it's important to carry out fertilizing and systematically inspect the underside of leaves for pests (aphids, butterfly eggs).

2.4. Head formation and filling

This stage is crucial for yield. Any stress during this period directly affects the quality of the head.

Typical symptoms and causes:

• Marginal necrosis (tissue death) of inner leaves. This is no longer just "marginal burn" but a serious physiological disorder — tipburn or internal necrosis, associated with calcium deficiency during rapid growth. The problem is often exacerbated by uneven watering (Kemble, 2022).
• Stopped head growth. The cause could be high temperatures (above 25 °C), which inhibit development, or severe pest damage, such as from aphids or cabbage white butterfly caterpillars (Welbaum, 2015).
• Softening of the head. Appearance of watery spots that quickly turn into rot with a foul odor — this is slimy bacteriosis. Particularly dangerous in rainy weather (Startsev, 2021).
• Cracking. A very characteristic problem for this stage. The head bursts due to a sharp change in moisture conditions (intensive watering or rain after drought). The outer leaves become tough and cannot withstand the pressure of the growing inner leaves (Welbaum, 2015).

Practical advice: At the head formation stage, uniform watering is especially important. Sharp moisture fluctuations are the main cause of cracking and bacterial rots.

2.5. Maturation and Storage (before harvest)

At the end of the season, problems are often related to the accumulation of infections before storage.

Typical symptoms and causes:

• Affected by gray and white mold. Especially in rainy and cold autumns. A fluffy gray (gray mold) or white with black dots (white mold) coating appears on the heads. These diseases are the main enemy during storage (Startsev, 2021).
• Abundant yellowing and dying off of lower leaves. This is a natural aging process, but if it happens too quickly, it could indicate root infection with Fusarium wilt or that the plant is simply not getting enough nutrients.

Practical advice: If you plan to store the cabbage, assess the condition of the heads 2–3 weeks before harvest. Yellowing and signs of rot signal that these heads should be used first.

Brief summary: Knowing which stage your cabbage is in allows you to assess risks more accurately. In early growth, care mistakes are most common; in mid-growth, issues with nutrition and water; and in late growth, storage diseases. Match the symptom with the stage, and you will quickly narrow down the possible causes.

3.1. Lower (Old) Leaves

These are the first leaves the plant produced. They often serve as an "indicator" of nutritional status, as the plant, when lacking mobile elements (nitrogen, potassium, magnesium), translocates them from old tissues to young ones.

What can be seen and what it indicates:

• Uniform yellowing, starting from the lowest leaves, gradually moving upward. This is a classic sign of nitrogen deficiency. The plant sacrifices older leaves to ensure the growth of new ones. If nitrogen fertilizer isn't applied, growth slows, and the head will be small (Kemble, 2022).
• Yellowing and browning of leaf edges ("marginal burn"), while veins remain green. This is a characteristic symptom of potassium deficiency. Often appears on light sandy soils (Welbaum, 2015).
• Yellowing between the veins (interveinal chlorosis) on old leaves, while the veins themselves stay green. This indicates a magnesium deficiency. Magnesium is an important part of chlorophyll; its deficiency often occurs on acidic soils (Nonnecke, 1989).
• Yellow or brown spots with concentric rings on old leaves. This resembles Alternaria (a fungal disease). Fungal spores activate in warm, humid weather and infect weakened leaves (Startsev, 2021).
• Massive yellowing and wilting of old leaves on one side of the plant. This could indicate the onset of Fusarium wilt or vascular bacteriosis, where vessels are affected, and nutrition is disrupted locally (Startsev, 2021).
• Chewed edges or holes in old leaves. Cause: caterpillars of cabbage white butterflies, cutworms, or moths, which start feeding on the lower, more accessible leaves (Nonnecke, 1989).

3.2. Upper (Young) Leaves and the Growing Point

This is the most important part of the plant, on which the future harvest depends. Problems here are generally related to a lack of "immobile" elements (calcium, iron, boron) or to viral and physiological diseases.

What can be seen and what it indicates:

• Yellowing between the veins, with veins remaining bright green, on the youngest leaves. This is classic iron deficiency (iron chlorosis). Occurs on alkaline soils or during waterlogging when roots cannot absorb iron (Nonnecke, 1989).
• Deformation, curling, wrinkling of young leaves, mosaic coloration (alternating light and dark areas). This could be a sign of a viral infection (e.g., cabbage mosaic virus). Viruses are transmitted by aphids and other sap-sucking insects. Deformation of the growing point can also be caused by damage from cabbage gall midge larvae (Startsev, 2021).
• Death (necrosis) of the growing point, plant "blindness." When the central bud blackens and dies, the cabbage stops forming a head. This can be a consequence of boron deficiency (B) on light soils or pest damage (Welbaum, 2015). Boron is a critically important micronutrient for cabbage, responsible for the growth of growing points (Pantyelyev, 1986).
• Spots and dying edges of young leaves inside the head. A very alarming symptom. This could be tipburn (internal necrosis). Cause: calcium deficiency during rapid growth. Calcium moves poorly within the plant, and its deficiency shows up in young tissues. Often provoked by uneven watering or excess nitrogen fertilizer (Kemble, 2022).
• Leaves covered with sticky residue. This is honeydew — a product of aphid or whitefly activity. The residue itself isn't dangerous, but sooty mold grows on it, hindering photosynthesis (Welbaum, 2015).

3.3. The Head (Outer and Inner Leaves)

Damage to the head is the most frustrating problem because the marketable product is affected. It's important to distinguish surface damage from internal rots.

What can be seen and what it indicates:

• Cracking (splitting) of the head. This is a physiological disorder. Cause: a sudden influx of water after a dry period. The skin of the head (outer leaves) becomes rigid and cannot withstand the pressure of the rapidly growing inner tissues (Welbaum, 2015).
• Watery, darkening spots that quickly soften and emit a foul odor. This is slimy bacteriosis (soft rot). It often starts at damaged spots or at the stump. Highly contagious in wet weather. Inside the head, leaves turn to mush (Startsev, 2021; Kemble, 2022).
• Dry, sunken, grayish or brownish spots with black dots on the outer head leaves. This could be Phoma (dry rot). If you cut the head, you can see darkening of the stump vessels. The disease progresses during storage (Startsev, 2021).
• Gray fluffy mold on the heads. This is gray mold. Usually appears on weakened or frost-damaged heads, especially in storage, but can also develop in the field during rainy summers (Startsev, 2021).
• White cottony mycelium with black hard formations (sclerotia). This is white mold. Affects the head at the base, often late in the season under high humidity (Startsev, 2021).

3.4. Stem (Stump) and Plant Base

This is the connecting link between roots and leaves. Problems here are often related to basal rots or soil-dwelling pests.

What can be seen and what it indicates:

• The root collar becomes dark, thins, and rots. This is classic "blackleg." Characteristic for seedlings, but also occurs on mature plants under waterlogging. The plant pulls out easily; roots may look normal (Startsev, 2021).
• Sunken, grayish or light brown spots with black dots appear on the stem at the base. This is Phoma. Unlike "blackleg," the tissue doesn't soften but remains dry. With severe infection, the stump may break (Startsev, 2021).
• The stem base and upper part of the root are covered with small swellings, resembling growths. This is the result of activity by the cabbage gall weevil or cabbage root fly larvae. The swellings can range from pea-sized to nut-sized (Startsev, 2021).
• The stump shows dark (almost black) rings in the vascular system when cut. This is a sign of vascular bacteriosis or Fusarium. Bacteria or fungus block the vessels, causing the plant to wilt (Startsev, 2021; Kemble, 2022).
• Colonies of grayish or greenish insects are visible on the stem surface and in leaf axils. This is cabbage aphid. It sucks sap, weakening the plant and transmitting viruses (Nonnecke, 1989).

3.5. Roots

Examining the roots is one of the most revealing but often overlooked steps. If the plant is wilting and there are no external signs of pests — dig it up and inspect the root system.

What can be seen and what it indicates:

• Fine roots are missing, they appear "eaten," and the main root looks like a stiff bristle. This is the work of cabbage root fly larvae, which eat root hairs and bore into the roots (Startsev, 2021).
• Swellings (galls) of various sizes form on the lateral roots. This is clubroot — one of the most dangerous diseases. Galls are initially white, then turn brown and decompose. Plants with clubroot are severely stunted and fail to form normal heads. The pathogen lives in the soil (Startsev, 2021; Nonnecke, 1989).
• Roots are brown, covered with ulcers, and easily break down. This could be infection with Phoma (dry rot), where the rot moves up from the roots along the stem, or other root rots (e.g., Rhizoctonia) (Startsev, 2021).
• Roots are simply missing or severely gnawed, with "tracks" visible. This could indicate wireworms (click beetle larvae) or cockchafer larvae. They gnaw through the roots, and the plant dies (Startsev, 2021).
• The main root is cut, and tunnels are visible around the planting hole. This is the "signature" of the mole cricket. It not only damages roots but also damages the plants themselves (Startsev, 2021).

Practical summary:

Symptom localization is your main "filter." If the problem is on old leaves — check nutrition (nitrogen, potassium). If the problem is at the growing point — look for boron or calcium deficiency, or a virus. If the problem is on the roots — the cause is almost always soil pests or pathogens like clubroot/rots. Always check the underside of leaves and the root system; this significantly increases the accuracy of your diagnosis.

4.1. Yellowing (Chlorosis)

Chlorosis is a disruption in chlorophyll formation. Leaves lose their green color, becoming yellow, pale green, or even white. This is one of the most common, yet most "multi-faced" symptoms.

• Uniform yellowing of old lower leaves. Classic sign of nitrogen deficiency (N). The plant sacrifices old leaves to support new growth. If not fertilized, yellowing will move higher, and the head will be small (Kemble, 2022).
• Yellowing of leaf edges (marginal chlorosis). Edges become yellow and dry, while the leaf center may remain green. This is a sign of potassium deficiency (K). Often appears on light soils or after drought (Welbaum, 2015).
• Interveinal chlorosis. The leaf blade turns yellow, while the veins stay green. On old leaves, this is magnesium deficiency (Mg); on young leaves, it's iron deficiency (Fe) (Nonnecke, 1989). In the first case, it's a soil problem; in the second, it's often related to soil pH (iron becomes unavailable in alkaline conditions).
• Yellowing on one side of the plant. If leaves on one side of the rosette turn yellow while the other stays green, this could indicate vascular bacteriosis or Fusarium wilt. The disease blocks vessels locally, disrupting nutrition on one side (Startsev, 2021).
• Mosaic yellowing. Alternating dark green and light yellow patches on the leaves. This almost always indicates a viral infection, transmitted by aphids (Startsev, 2021).

4.2. Wilting

The plant loses turgor, leaves and stem become soft and limp. This is always related to water uptake issues.

• Wilting in hot weather, but recovering by evening. This could simply be a lack of moisture in the soil. However, if the plant doesn't recover after watering, it's a serious symptom (Pantyelyev, 1986).
• Wilting with moist soil. This is the most alarming sign. It indicates roots cannot absorb water. Causes: vessel blockage (Fusarium, bacteriosis), root damage (cabbage root fly larvae, mole cricket, clubroot), or root rot (Kemble, 2022; Startsev, 2021).
• Wilting and yellowing. If wilting is accompanied by yellowing of old leaves, it often indicates root rots or damage to the root system, preventing adequate water and nutrient uptake.

4.3. Spots

Spots are localized areas of dead or altered tissue. Their shape, color, and the presence of a border are key to diagnosis.

• Brown or gray spots with concentric rings ("targets"). This is characteristic of fungal diseases in the Alternaria and Cercospora groups. Often affect old leaves in wet weather (Startsev, 2021).
• Watery, rapidly enlarging spots that become slimy and emit a foul odor. This is slimy bacteriosis (soft rot). Spreads quickly inside the head, especially in warm, humid weather (Startsev, 2021).
• Small black or dark brown spots on the underside of the leaf. This could be the initial stage of downy mildew (Peronospora). A whitish coating appears on the underside of the spots (Welbaum, 2015).
• Gray, sunken spots with black dots on the stem and head. This is a sign of Phoma (dry rot). Spots are not wet, but dry and sunken. The black dots are fungal pycnidia (Startsev, 2021).
• Small black dots or "speckling" on the veins. Can be a symptom of viral diseases or a physiological disorder, e.g., internal necrosis due to calcium deficiency (Welbaum, 2015).

4.4. Deformation (Change in Shape)

Disruption of the normal shape of leaves, stem, or head is always a sign of a serious growth malfunction.

• Leaf curling and crinkling. Young leaves grow unevenly, curling downwards or upwards. This is a typical sign of a viral infection (mosaic) or damage from aphids. It can also be related to uneven watering (Welbaum, 2015; Startsev, 2021).
• Thickening and bending of petioles. If leaf petioles become thick and bent, this could be damage from cabbage gall midge or stem weevil (Startsev, 2021).
• Misshapen head. Instead of one large head, the plant forms several small, deformed "heads." This is often the result of damage to the apical growing point. Causes: flea beetle, cabbage gall midge, mechanical damage, or severe stress (Nonnecke, 1989).

4.5. Growth Stagnation

The plant seems to "freeze." Leaves stop increasing in size, the head doesn't set. This is a symptom of complex stress.

• Stunted growth after transplanting. Cause: root damage during transplanting, cold weather, lack of moisture, or pest damage.
• Stunted growth during active vegetation. Most often it's nutrient deficiency (especially nitrogen), drought, or root system damage (clubroot, root rot) (Kemble, 2022).
• "Sitting seedling" disorder. A variety that forms a dense leaf rosette but doesn't start heading ("Rigoletto"). This could be related to high temperatures, lack of moisture, or a genetic characteristic of the variety (Welbaum, 2015).

4.6. Rotting

Rot is the decomposition of tissues caused by bacteria or fungi. Always dangerous, especially in wet weather.

• Soft, slimy rot with a foul odor. This is bacterial rot. Affects heads, root collar, especially in rainy weather (Startsev, 2021).
• Dry rot. Tissues become dry, crumbly, and have no odor. This is characteristic of Phoma and Fusarium. Cutting the stem reveals darkened vessels (Startsev, 2021).
• Rot with fluffy coating. Gray or white coating indicates fungal diseases, commonly known as gray and white mold. Appear on weakened or frost-damaged plants (Startsev, 2021).

4.7. Necrosis (Tissue Death)

Necrosis is the "death" of a tissue area. It can be caused by infection, element deficiency, or external damage.

• Dying leaf edges ("marginal burn"). Areas along the leaf edge become dry and brown. This is a classic symptom of potassium deficiency (Nonnecke, 1989).
• Internal necrosis (death of inner leaves). Small dark spots appear on inner leaves, which later die off. This is tipburn, associated with calcium deficiency (Ca) during rapid growth. Particularly common in hybrids (Kemble, 2022; Welbaum, 2015).
• Necrosis of the growing point. The central bud blackens and dies. The plant cannot develop further. Cause: boron deficiency (B). Boron is essential for the growth of all growing points (Nonnecke, 1989).

4.8. Cracking

Loss of integrity of the head.

• Single split (cracking). The most common cause is sharp changes in moisture (heavy watering or rain after drought). Inner leaves grow faster than outer ones, causing the head to burst. This is a physiological disorder, unrelated to diseases (Welbaum, 2015).
• Multiple small cracks. Can be caused by pest damage or fungal diseases weakening the head's structure.

Brief summary: The ability to classify symptoms is the first and most important step towards a diagnosis. When you see a yellow leaf, ask yourself: "What type of yellowing is this?" When you notice a spot, ask: "Is it dry, wet, or has a coating?" The answers to these questions will significantly shorten the list of possible causes.

The next chapter (5) will teach us to distinguish between diseases and nutrient deficiencies — one of the most challenging aspects of diagnosis. Shall we move on to it?

5.1. Symmetry of the Damage

• Deficiencies: Generally appear symmetrically. Nitrogen, potassium, or magnesium deficiency affects all plants roughly equally and on all sides of the plant. If it's lower leaves, they will yellow uniformly on all sides of the plant, not just on one side (Welbaum, 2015).
• Diseases: Often appear asymmetrically or locally. For example, spots may appear only on one side of a leaf or only on leaves facing the sun. Fungal infections often start as individual spots that lack clear symmetry. A disease may affect individual plants or groups of plants in the field (Startsev, 2021).

5.2. Locality and Pattern of Spread

• Deficiencies: Spread through the plant depending on the mobility of the element. Mobile elements (nitrogen, potassium, magnesium) move from old leaves to young ones, so their deficiency shows up on lower leaves. Immobile elements (calcium, boron, iron) cannot move, so their deficiency is seen on young, terminal leaves and at the growing point (Kemble, 2022). In the field, a deficiency usually appears more or less evenly across the entire bed, unless there are strong differences in the soil.
• Diseases: The method of spread varies. Fungal diseases often start as individual spots that eventually merge. Bacterial diseases can spread rapidly within the plant and between plants, especially in wet weather. Viruses often cause mosaic patterns visible only on specific parts of the leaf (Startsev, 2021). Diseases may appear as foci (groups of affected plants), not uniformly across the entire area.

5.3. Speed of Development

• Deficiencies: Develop gradually. A deficiency doesn't appear in a day; it accumulates slowly over several days or weeks. You might notice the yellowing increasing slowly (Welbaum, 2015).
• Diseases: Depending on the type, they can develop rapidly or very rapidly. Bacterial soft rot can turn a healthy head into a slimy mass in a few days. Downy mildew, under favorable (humid) conditions, can occupy a plant in 5–7 days. Fungal infections also often progress rapidly (Startsev, 2021).

5.4. Connection to Weather and Agricultural Practices

• Deficiencies: Often related to soil type, incorrect fertilization, or conditions affecting uptake. For example, iron deficiency often shows up on alkaline soils. Cold weather slows phosphorus uptake. Potassium deficiency is exacerbated on light soils after heavy rains. If you know your soil and know you haven't applied potassium, and there's dry weather, it's logical to suspect potassium deficiency (Nonnecke, 1989).
• Diseases: Their development is closely linked to specific weather conditions. Most fungal diseases (Alternaria, downy mildew, gray mold) are activated in wet, rainy, warm, or conversely cool weather. If you notice spots on leaves right after a period of prolonged rain, it's likely a fungal infection (Startsev, 2021). Viruses spread actively when there's a mass flight of aphids (the vector).

5.5. Presence of an Infectious Pattern

• Deficiencies: Lack signs of infection. There is no mycelium, spores, or putrid smell on affected leaves (unless it's rot, but rot is often secondary, attacking a weakened plant). There's no characteristic fluffy coating, no black dots (pycnidia) on stems characteristic of Phoma (Startsev, 2021).
• Diseases: Have specific signs of the pathogen. This is the key difference! In fungal diseases, a coating (white, gray, black) is often visible. In bacteriosis, there are slimy exudates and a characteristic putrid smell. In Phoma, there are black dots (pycnidia) on the spots (Kemble, 2022). Viruses often cause mosaic coloration, leaf curling, and stunting.

Practical examples for comparison:

• Old leaves turning yellow. If the yellowing is uniform and covers the whole plant, it's likely nitrogen deficiency. If leaf edges turn yellow and dry while the rest of the leaf is green, it's potassium deficiency. If the yellowing is mosaic (alternating with green), it's a virus (Startsev, 2021; Welbaum, 2015).
• Spots on leaves. If spots are dry with concentric rings, appear in wet weather, and lack clear symmetry, it's a fungal disease (Alternaria). If spots are small, pinpoint, without a clear shape, and accompanied by wilting, it could be bacteriosis. If there's a white coating on the underside of the spots, it's downy mildew. If spots appeared after a sharp weather change (drought → rain), it could be tipburn (calcium deficiency) (Startsev, 2021; Nonnecke, 1989).
• Wilting. If the plant wilts but recovers after watering, it's drought. If it wilts in moist soil and dark vessels are visible when the stem is cut, it's vascular bacteriosis or Fusarium (infection blocking the vessels). If roots are damaged (swellings, gnawed), it's pests (clubroot, cabbage fly, mole cricket) (Startsev, 2021; Kemble, 2022).
• Growing point dying. If the growing point turns black but the plant otherwise looks healthy, it's boron deficiency. If the growing point is damaged and there are signs of insects nearby (holes, excrement), it's pest damage (Nonnecke, 1989; Startsev, 2021).

Brief summary: To distinguish a disease from a deficiency, always ask yourself these questions:

1. Is the damage uniform? (Symmetric → deficiency; local/asymmetric → infection).

2. How fast is the problem spreading? (Slowly → deficiency; rapidly → infection).

3. Are there obvious signs of a pathogen? (Coating, pycnidia, putrid smell, mosaic → infection; absent → deficiency).

4. Is the problem related to the weather? (Prolonged rains → fungi; drought → deficiency or physiological stress).

Never start with pesticides. Always check first if your plant is hungry. Often the "treatment" is simply fertilization.

6.1. Feeding Traces — The Main Clue

Pests leave very characteristic "autographs." Your job is to see them and interpret them correctly.

• Holes and chewed leaf edges. This is the most obvious sign. It's left by caterpillars (cabbage white, cutworm, moth) and beetles (flea beetles, leaf beetles). If leaf edges are chewed and you see green caterpillars or shiny black bugs on the plant, there's no doubt (Nonnecke, 1989).
• "Mines" — winding tunnels inside the leaf blade. This is the work of diamondback moth larvae or leaf-mining flies. The larva lives inside the leaf, eating the flesh, and leaves a light, winding trail. From the outside, it looks like transparent "tunnels" (Startsev, 2021; Pantyelyev, 1986).
• "Skeletonization" of leaves. When only the veins, resembling a skeleton, remain, and the flesh is completely eaten. This is characteristic of a mass invasion of cabbage cutworm or white butterfly caterpillars. They can almost completely destroy a leaf (Startsev, 2021).
• Damage to the head (internal tunnels). If the head looks healthy but upon cutting reveals tunnels and dark spots, this is likely the work of cabbage cutworm caterpillars. They penetrate the head and gnaw tunnels, contaminating it with excrement (Startsev, 2021; Nonnecke, 1989).
• Gnawing on roots and stems at the base. Cabbage root fly larvae, mole crickets, wireworms, cockchafer larvae — all damage the underground part. If the plant wilts and pulls out easily, and there are signs of gnawing, tunnels, or larvae on roots and the stem base, the cause is soil pests (Startsev, 2021; Pantyelyev, 1986).
• Swellings on roots (galls). It's important to remember that galls can be caused by both pests (root weevils) and diseases (clubroot). The difference is that with clubroot, the galls soften and rot, whereas with weevils, they are denser, and you can find a larva or the tunnel it made inside (Startsev, 2021).

6.2. Excrement and Byproducts

They often reveal the presence of pests better than the damage itself.

• Caterpillar frass (excrement). Dark small pellets or crumbs visible on leaves or near the damaged area. This is a sure sign that caterpillars are feeding on the plant (Nonnecke, 1989).
• Honeydew (sticky coating). Transparent, sticky droplets on leaves and stems. This is a byproduct of aphids, whiteflies, and other sap-sucking insects. Sooty mold often grows on this sticky coating, appearing as a black film. If you see stickiness and ants running over the plants, look for aphids (Welbaum, 2015; Startsev, 2021).
• Webbing. Fine webbing on the underside of leaves or between them indicates spider mites. This is not a disease but a pest, albeit microscopic. The web is its characteristic sign (Kemble, 2022).

6.3. Holes and Tunnels in Stems and Heads

• Holes in the stump. If the stem (stump) has holes through which a tunnel is visible, or if tunnels are visible on a cut, this is the work of stem cabbage weevil larvae, cabbage gall midge, or cutworm (Startsev, 2021).
• Tunnels inside the head. Only discovered when cutting the head. This is a clear sign of cabbage cutworm caterpillars. They are difficult to see from the outside, but sometimes there are entry holes surrounded by frass (Nonnecke, 1989).

6.4. Insect Colonies

The surest sign is seeing the pests themselves or their egg masses.

• Aphid colonies. Aphids settle in colonies on the underside of leaves, on shoot tips, and in leaf axils. They are small, greenish, greyish, or black. If you turn a leaf and see a cluster of small insects, it's aphids. Often ants "herd" them nearby (Welbaum, 2015).
• Butterfly egg masses. On the underside of leaves, you can find clusters of small, pale yellow or greenish eggs. These are butterfly eggs (whites, cutworms, moths). If you see such clusters, caterpillars will hatch within a few days (Pantyelyev, 1986).
• Caterpillars. They are hard to miss if you know where to look. They are most often found on the underside of leaves, along the veins, or on the central leaves of the rosette. Green, grey, or striped, with a distinct body segmented.
• Beetles. Flea beetles are small, jumping, shiny black bugs that jump at the slightest danger. Weevils are beetles with a long snout, often sitting on stems and petioles. If you see them on the plant, they are there for a reason (Nonnecke, 1989).

6.5. How to Tell Damage from Diseases: Practical Signs

Examples for reinforcement:

• Situation: Small holes and "shot-hole" damage appear on leaves. Conclusion: This is the flea beetle. Treating a disease is useless. Insecticides or folk remedies (ash, tobacco dust) are needed. Diseases don't cause such small, through holes (Nonnecke, 1989).
• Situation: The plant is wilting. You pull it out and see tunnels and white, legless larvae in the roots. Conclusion: These are cabbage root fly larvae. Treating root rot (if present) is too late, and it is secondary. The main cause is the pest. Measures to control larvae in the soil are needed (Startsev, 2021).
• Situation: Clusters of small grey insects on the underside of leaves. Conclusion: This is aphids. They weaken the plant. Applying fungicides is useless. Systemic insecticides or biologicals against aphids are needed, or attracting entomophages (ladybugs) (Welbaum, 2015).
• Situation: A white "cottony" growth with black dots appears on the head. Conclusion: This is a disease (white mold), not a pest. No insect is there. Remove the diseased head immediately to prevent the infection from spreading, and use fungicides on healthy plants (Startsev, 2021).

Brief summary: Carefully inspect your plants. Look for the pests themselves or their signs (frass, tunnels, eggs). If they are absent, it's a disease or deficiency. If present, the cause is clear. The main rule: find the culprit first. Do not start treatment without evidence.

The next chapter will focus on physiological disorders, which are often confused with diseases and pests. Shall we proceed?

7.1. Connection to Weather

This is one of the main criteria. If the problem started synchronously with a sudden change in weather, it's almost certainly a physiological disorder.

• Heat (above +25 °C) and drought. Cabbage is a cold-hardy crop. At high temperatures, growth slows, leaves lose turgor, and leaf edges may dry out and curl. Wilting in the heat is a natural response. If the plant recovers by evening, it's a protective reaction, not a disease. However, if the heat persists, real problems can start (Welbaum, 2015).
• Frost. Spring and autumn frosts can damage leaves, especially young ones. Damaged tissues become watery, transparent, then turn brown and die. Understand that this is not a disease but mechanical damage from cold. It cannot be treated! Affected leaves should be removed to prevent them from becoming a source of infection (Pantyelyev, 1986).
• Sharp temperature fluctuations. Cold nights, hot days. This is stress for the plant, which can trigger "internal necrosis" and other disorders. It also contributes to head cracking (Welbaum, 2015).
• Prolonged rains and waterlogging. When roots are in water for a long time, they begin to suffocate and rot. This leads to wilting and yellowing of leaves, especially old ones. Symptoms resemble Fusarium, but unlike infection, the problem disappears after the water regime normalizes (Nonnecke, 1989).

Key test: If symptoms begin to disappear after favorable weather arrives, it was likely a physiological disorder caused by weather stress.

7.2. Connection to Watering (Water Regime)

Cabbage is a very moisture-loving crop. Disruption of the water regime is a major cause of physiological problems.

• Lack of moisture. If the soil is dry and the plant wilts (loses turgor), but recovers quickly after watering, the cause is obvious. Chronic moisture deficiency leads to growth stunting, death of lower leaves, and formation of small, loose heads (Welbaum, 2015).
• Excess moisture. If the soil is waterlogged, roots suffer from lack of oxygen. The plant wilts, turns yellow, and rots. It's important to distinguish this from bacteriosis: in bacteriosis, the rot has a characteristic smell and affects a specific organ. With waterlogging, it's general wilting and yellowing without localized rot (Nonnecke, 1989).
• Sharp moisture fluctuations. This is the classic cause of head cracking. After a dry period, the outer leaves of the head become rigid, and then heavy watering or rain follows. Inner leaves grow rapidly and rupture the "clothing" outside. This is not a disease but a purely physical phenomenon (Welbaum, 2015; Kemble, 2022).

7.3. Connection to Fertilization (Nutrition)

Nutrient deficiency is also a physiological disorder, although we discussed distinguishing it from diseases separately in a previous chapter.

• Excess fertilizer. Too high a salt concentration in the soil burns the roots. The plant looks stunted, leaves wilt even in moist soil, and leaf edges may turn brown. This often happens when applying large doses of undecomposed manure or exceeding mineral fertilizer rates.
• Element imbalance. For example, excess nitrogen can interfere with potassium and calcium uptake, provoking "internal necrosis" and increasing pest damage. Excess potassium can cause magnesium deficiency (Nonnecke, 1989).

Key test: If you know for sure you didn't apply a certain fertilizer and the leaves started yellowing, or conversely, you over-fertilized, it's logical to link the symptoms to nutrition. Check when you last fertilized and at what rates.

7.4. Absence of an Infectious Pattern

This is the decisive criterion. In physiological disorders, there is never:

• Mycelium and spores on the leaf or stem surface.
• A putrid smell.
• Characteristic "entry points" for infection (no specific site damage, vessel blockage, etc.).
• Coating (white, grey, black).
• Black dots (pycnidia), characteristic of Phoma (Startsev, 2021).

A physiological disorder looks like an "error" in the plant's own functioning, not the result of an external attack.

7.5. Examples of Common Physiological Disorders

• Tipburn (internal necrosis). Small dead areas on the edges of young leaves inside the head. Cause: calcium deficiency during rapid growth. The symptoms are not an infection but tissue necrosis arising from a lack of "building material" for cell walls. Often occurs with uneven watering and excess nitrogen (Kemble, 2022).
• Internal spotting. Small black dots on the inner leaves of the head. Resembles fungal diseases, but this is also calcium starvation. It intensifies during storage but begins in the field (Welbaum, 2015).
• Head cracking. Mechanical damage due to a sudden influx of water. The outside of the head is covered with cracks, but inside it can be perfectly healthy. This is not rot (Startsev, 2021).
• Sunburn. If the head is exposed to direct scorching sun, outer leaves can get burned: they become pale, whitish, then turn brown and die. Plants with insufficient leaf rosette development suffer especially (Pantyelyev, 1986).
• Frost damage. Watery, transparent spots on leaves that later turn brown and dry.

Brief summary: How to recognize a physiological disorder?

1. Weather: The problem arose abruptly after frost, heat, drought, or waterlogging.

2. Watering: There are clear water regime issues (overwatering or underwatering).

3. Nutrition: There is a clear link to recent fertilization or its absence.

4. Absence of pathogen signs: No coating, spores, rot, odor, or pests visible.

5. Non-contagiousness: Individual plants or leaves are affected, but there is no focal spread typical of infections.

If you suspect a physiological disorder, don't treat the plant. Change the conditions: regulate watering, provide shade, adjust fertilization. Often, this is the only way to help the plant.

8.1. Leaves Are Yellowing

If old (lower) leaves turn yellow and dry, and the yellowing spreads from bottom to top:

• Diagnosis: Most likely, nitrogen deficiency (N) . The plant uses reserves from old leaves to grow new ones (Kemble, 2022).
• What to do: Apply nitrogen fertilizer (urea, ammonium nitrate). Preferably in liquid form for quick uptake.
• Why it matters: Nitrogen is the main element for green mass growth. Its deficiency immediately affects yield.

If leaf edges are yellowing (marginal chlorosis):

• Diagnosis: Potassium deficiency (K) . Edges turn yellow and dry, while the central part of the leaf may remain green (Nonnecke, 1989).
• What to do: Apply potassium fertilizer (potassium sulfate, potassium magnesium sulfate). Especially relevant on light sandy soils.
• Why it matters: Potassium is responsible for water exchange and tissue strength. Its deficiency makes the plant vulnerable to drought and diseases.

If young leaves turn yellow, but veins remain green:

• Diagnosis: Iron deficiency (Fe) , less commonly manganese or zinc. Iron is poorly absorbed in alkaline soils (pH above 7.0) or under waterlogging (Nonnecke, 1989).
• What to do: Apply foliar feeding with iron chelate. If the pH is the cause, acidify the soil.
• Why it matters: Iron is involved in chlorophyll formation. Without it, the plant cannot photosynthesize.

If the yellowing is mosaic, with alternating light and dark areas:

• Diagnosis: Viral infection (cabbage mosaic). Transmitted by aphids (Startsev, 2021).
• What to do: Remove and destroy the diseased plant. Control aphids (the vector). No chemical treatment exists for viruses.
• Why it matters: The virus is untreatable. It's crucial to prevent its spread to other plants.

If only the leaves on one side of the plant turn yellow:

• Diagnosis: Likely vascular bacteriosis or Fusarium wilt. The disease blocks vessels on one side (Startsev, 2021).
• What to do: Remove the diseased plant. In the initial stage, try treatment with biological products. Practice crop rotation in the future.
• Why it matters: This is an infection that spreads through soil and plant debris.

8.2. Wilting

If the plant wilts but recovers after watering:

• Diagnosis: Lack of moisture (drought) (Pantyelyev, 1986).
• What to do: Ensure regular, even watering.
• Why it matters: Cabbage consumes a lot of water, especially during head formation. Dry soil drastically reduces yield.

If the plant wilts in moist soil and does not recover after watering:

• Diagnosis: Root problems or vessel blockage. Causes:
  • If roots are gnawed, tunnels visible: Soil pests (cabbage root fly larvae, mole cricket, wireworm) (Startsev, 2021).
  • If roots have swellings (galls): Clubroot (Startsev, 2021).
  • If dark vessels are seen on the cut stem: Vascular bacteriosis or Fusarium (Startsev, 2021; Kemble, 2022).
• What to do: Dig up the plant and inspect the roots. Remove the diseased plant. For pests — apply insecticides; for clubroot — lime the soil and practice crop rotation.
• Why it matters: This is the most alarming signal. The cause is almost always a serious problem that needs rapid diagnosis.

If wilting is accompanied by massive yellowing and occurs in hot weather:

• Diagnosis: Could be Fusarium wilt, which activates at high temperatures (above +25 °C) (Kemble, 2022).
• What to do: Remove affected plants. Water to reduce stress.
• Why it matters: Fusarium is a soil-borne infection. The main protection is resistant varieties and crop rotation.

8.3. Spots on Leaves

If spots are dry, with concentric rings (target-like), appearing in wet weather:

• Diagnosis: Fungal disease (most commonly Alternaria) (Startsev, 2021).
• What to do: Treat with a fungicide (preferably systemic). Remove severely affected leaves. Ensure ventilation.
• Why it matters: Fungi activate under high humidity. Prevention is more important than cure.

If spots are watery, rapidly enlarging, and emit a foul odor:

• Diagnosis: Slimy bacteriosis (soft rot) (Startsev, 2021; Kemble, 2022).
• What to do: Immediately remove diseased heads to prevent infection spread. Chemical treatment is ineffective.
• Why it matters: This is a highly contagious and rapidly spreading disease. It's crucial to isolate the outbreak.

If there's a white or greyish coating on the spots (on the underside):

• Diagnosis: Downy mildew (Peronospora) (Welbaum, 2015).
• What to do: Treat with a fungicide. Improve ventilation, avoid getting water on the leaves.
• Why it matters: The disease likes cool, damp weather. Often appears on seedlings.

If spots are gray, sunken, with black dots inside:

• Diagnosis: Phoma (dry rot) (Startsev, 2021).
• What to do: Remove affected plants. Use healthy seeds and practice crop rotation in the future.
• Why it matters: The disease is dangerous not only in the field but also during storage.

8.4. Deformation and Growth Stagnation

If leaves curl, wrinkle, or grow malformed:

• Diagnosis: Viral infection (mosaic, leaf curl) or aphid damage (Welbaum, 2015; Startsev, 2021).
• What to do: Remove the diseased plant. Control aphids.
• Why it matters: Viruses are incurable. All efforts focus on controlling the vectors.

If the growing point dies ("blind" plants):

• Diagnosis: Boron deficiency (B) or damage to the apical bud by insects (Nonnecke, 1989; Startsev, 2021).
• What to do: Apply boron (foliar feeding) and check for pests.
• Why it matters: Boron is a critically important micronutrient for cabbage. Its deficiency leads to crop loss.

If the plant doesn't form a head (or the head is small), stunted growth:

• Diagnosis: Stress (drought, heat, waterlogging), nitrogen deficiency, root damage (clubroot, nematodes), or unsuitable variety for the climate (Welbaum, 2015).
• What to do: Check watering, fertilization, root condition. If all is well, the variety might be at fault.
• Why it matters: Heads don't form when the plant experiences stress. Remove the stress, and the yield appears.

8.5. Head Is Loose and Soft

• Diagnosis: Nutrient deficiency (most often potassium), excess nitrogen (plant "luxuriates"), lack of moisture, or a characteristic of late-maturing varieties that ripen towards autumn (Kemble, 2022).
• What to do: Apply potassium, improve watering.
• Why it matters: A firm head indicates good care.

8.6. Head Cracking

• Diagnosis: Physiological disorder — sharp moisture fluctuation (drought, then heavy watering or rain). Inner leaves grow faster than outer ones, splitting the head (Welbaum, 2015).
• What to do: Prevent sharp moisture fluctuations. Heads that have already cracked should be harvested — they don't store well.
• Why it matters: This is the most common problem, often confused with disease. There is no disease here. The solution is solely in agricultural practices.

8.7. Rotting at the Base and Stem

If sunken, gray or light spots with black dots appear at the stem base:

• Diagnosis: Phoma (dry rot) (Startsev, 2021).
• What to do: Remove affected plants. This is a fungal disease spreading through seeds and plant debris.

If the stem base darkens, thins, and rots (on seedlings or mature plants):

• Diagnosis: "Blackleg" — a fungal disease developing under waterlogging, overcrowding, and poor ventilation (Startsev, 2021).
• What to do: For seedlings — thin them, reduce watering, ensure ventilation. Treatment is ineffective.
• Why it matters: This is a disease of weakened plants. Healthy, hardened plants are less susceptible.

8.8. Head Rot (Outer or Inner Leaves)

• If rot is soft, wet, smelly: Slimy bacteriosis. Immediately remove diseased heads (Startsev, 2021; Kemble, 2022).
• If rot is dry, with black dots: Phoma. Remove, use fungicides (Startsev, 2021).
• If there's a fluffy coating (white or gray): White or gray mold. Remove. These are fungal diseases, especially dangerous during storage (Startsev, 2021).

8.9. Holes, Tunnels, Chewed Leaves Visible on the Plant

• Diagnosis: Pests (Nonnecke, 1989; Startsev, 2021).
• What to do: Identify the pest and apply the appropriate insecticide or biological product.
• Why it matters: Mechanical damage is not a disease. You need to fight the specific insect.

Final advice:

Remember the golden rule: Always look for the cause, not just treat the symptom. Check the roots, inspect the underside of leaves, analyze the weather and your actions. If in doubt, start with the simplest: check soil moisture and conduct preventive fertilization. Often the problem is solved at this stage.

Only a systematic approach, combining knowledge of symptoms, localization, growth stages, and plant physiology, will allow you to accurately diagnose the problem and make the right decision. We hope this article helps you grow healthy and delicious cabbage!