Diseases

How to Recognise Cercospora Leaf Spot

The first signs usually appear in midsummer, when the plants have developed 10–15 true leaves. Small (2–5 mm in diameter) round spots of greyish‑yellow or ash colour appear on the leaf blades. The main distinguishing feature is a reddish‑brown or dark‑purple border around the spot (Autko et al., 2012). Over time, the spots enlarge to 1 cm, may merge with each other, covering large areas of the leaf. In wet weather, a greyish‑white velvety coating appears on the surface of the spots—these are fungal spores that are spread by wind and rain, infecting new leaves.

Severely affected leaves turn yellow, dry up and die. Only the youngest leaves remain in the centre of the rosette, but they too soon become infected. The plant spends energy on growing new tops at the expense of root growth.

Conditions Favourable for Cercospora Development

• Warmth and moisture. The fungus actively develops at +25…+30 °C and high relative humidity (above 80%). Periods when heat follows rain are especially dangerous.
• Dense sowings. In thick plantings, leaves stay wet longer after dew or rain, and air circulation is poorer—this creates ideal conditions for infection.
• Failure to observe crop rotation. If beets are grown in the same place for several years in a row, infection accumulates in the soil and on plant residues.
• Weeds from the Chenopodiaceae family (lamb’s quarters, goosefoot, amaranth) serve as an additional reservoir for the fungus, from which it moves to cultivated plants.

How to Control Cercospora Leaf Spot

Since Cercospora is a disease that develops rapidly and causes great damage, control must be comprehensive.

1. Agronomic measures (prevention)

• Crop rotation. Return beets to their original place no earlier than after 3–4 years. On plots where Cercospora occurred in the previous season, this period should be extended to 5 years.
• Destruction of plant residues. After harvest, carefully collect and burn the tops or incorporate them deeply into the soil (20–25 cm). The fungus survives on the soil surface for up to 22 months, but when buried deeper than 10 cm, its viability drops to 10 months (Pethybridge et al., 2018).
• Weed control. Regularly weed the beds, especially removing Chenopodiaceae weeds both inside the crops and along the edges of the plot.
• Correct sowing dates. Sow beets at the optimal time, when the soil warms up to +6…+8 °C. Delaying sowing may cause the period of most intensive leaf development to coincide with heat and humidity, which will enhance disease development.

2. Choice of resistant varieties

No variety is absolutely resistant to Cercospora, but some are less affected. For example, the hybrid Boro (F1) and the variety Detroit Short‑Top show increased tolerance (Akhatov et al., 2013). In New York conditions, the variety Ruby Queen, popular for processing, turned out to be less susceptible than many other varieties (Pethybridge et al., 2018). When choosing seeds, check with the seller about the variety’s resistance to Cercospora.

3. Chemical protection

If the disease has already manifested, it is difficult to do without fungicides. However, it is important to apply them correctly:

• The first treatment is carried out when the first spots appear on the leaves (usually in late July – early August).
• Interval between treatments — 12–15 days. During the season, 2–4 sprays may be required, especially in a rainy summer.
• Preparations:
• Copper‑containing fungicides (1% Bordeaux mixture, copper oxychloride, Abiga‑Pik). These are contact preparations, they do not penetrate the plant, so thorough coverage of leaves is required. Consumption of Bordeaux mixture — 6–8 kg/ha (or 60–80 g per 10 L of water per 100 m²) (Karataev and Sovetkina, 1984).
• Systemic fungicides — Falcon (0.5–0.6 L/ha), Quadris (3 L/ha), Rex Duo (according to the instructions). They penetrate plant tissues and protect from the inside.
• Biopreparations — Alirin‑B, Gamair, Fitosporin‑M. They are less effective when the disease is severe, but can be used for prevention in organic farming. Spraying is carried out every 7–10 days (Akhatov et al., 2013).

Important warning! The fungus Cercospora beticola quickly develops resistance to fungicides from the strobilurin group (for example, to azoxystrobin, the active ingredient of Quadris). In New York, up to 81% of fungal isolates were resistant to this preparation (Pethybridge et al., 2018). Therefore, be sure to alternate preparations with different mechanisms of action — for example, copper‑containing and systemic ones. Do not use the same fungicide more than twice per season.

How to Recognise Powdery Mildew

Symptoms appear in the first half of summer. On the upper side of the leaves, separate white powdery spots appear, which quickly grow and cover the entire blade, and then spread to petioles and even stems (if the plant bolts). The coating resembles flour or ash. Under it, the leaf tissue turns yellow, becomes brittle, and leaves prematurely age and dry out. In the second half of summer, small black dots can be seen on the coating—these are the fruiting bodies of the fungus (cleistothecia), in which it will overwinter on plant residues (Autko et al., 2012).

Conditions for Development

• Hot dry weather (above +25 °C) combined with morning dews.
• Dense plantings and poor ventilation.
• Excess nitrogen fertilisers, which make leaf tissues more loose and susceptible to the fungus.
• Overhead watering in hot weather (water droplets on leaves promote spore germination).

How to Control Powdery Mildew

1. Prevention

• Observe crop rotation and remove plant residues—the fungus overwinters on them.
• Do not overfeed beets with nitrogen, especially in the second half of summer. Prefer potassium and phosphorus fertilisers, which increase plant resistance.
• Water at the root, avoiding water on the leaves.
• Thin out seedlings to ensure good ventilation between plants.

2. Biological and chemical means

• Sulphur. Treatment with colloidal sulphur (1% suspension) or ground sulphur with lime (1:1) at a rate of 15–20 kg/ha (Balashev and Zeman, 1981). In a hobby garden, take 30–40 g of colloidal sulphur per 10 L of water. Spraying is carried out at the first signs of the disease, repeated after 7–10 days.
• Biopreparations — Alirin‑B, Gamair, Fitosporin‑M (indicated for organic cultivation).
• Chemical fungicides — Topsin‑M, Falcon, Recruit. However, in Russia, many preparations are not registered for table beet against powdery mildew, so refer to local recommendations (Akhatov et al., 2013). In Ukraine and Belarus, the list of permitted preparations may be wider.

How to Recognise Phoma on Leaves

On adult leaves, large (5–15 mm) round or irregularly shaped spots of yellowish or light‑brown colour appear. Unlike Cercospora, Phoma spots have concentric zones — like tree rings (Autko et al., 2012). On closer inspection, many small black dots can be seen on the spots—these are the pycnidia of the fungus, where spores mature. Affected leaves turn yellow and die, starting with the lower, older ones.

On petioles and stems, Phoma appears as elongated dark‑brown necrotic streaks. On seed plants, the fungus infects inflorescences, causing blackening and death of flowers.

Conditions for Development

• Cool and humid weather (optimal temperature for infection +15…+20 °C).
• Boron deficiency in the soil. Boron starvation weakens root tissues and makes them more vulnerable to Phoma (Autko et al., 2012).
• Storage of infected mother roots—the fungus survives in them and infects seed plants in spring.

How to Control Phoma

1. Prevention

• Crop rotation (3–4 years).
• Destruction of plant residues.
• Application of boron to the soil or foliar feeding with boric acid (1.5–3 kg/ha a.i., or 15–20 g per 10 L of water per 100 m²). Boron not only prevents Phoma but also improves root quality (Balashev and Zeman, 1981).
• Liming of acid soils (pH not below 6.0).

2. Fungicide treatments

The same measures as for Cercospora. Copper‑containing preparations (Bordeaux mixture, copper oxychloride) are especially effective. Spraying is carried out when the first symptoms appear and repeated after 12–15 days.

How to Recognise Seedling Rot

Seedling rot appears shortly after emergence, most often in the “cotyledon” stage or with 1–2 true leaves. The main signs:

• Darkening and browning of the root collar and hypocotyl (the section of stem between the root and cotyledons).
• Tissues become watery, soft, then blacken and thin—a characteristic “constriction” forms.
• The plant lodges and dries up.
• A coating (pink, grey, or white—depending on the pathogen) may appear on the affected areas.
• Seedlings emerge unevenly, sparsely, and “bald patches” are visible in the field.

Sometimes seedling rot affects sprouts even before they emerge—in this case, seeds rot in the soil, and there are no seedlings at all.

Conditions Favourable for Development

Most seedling rot pathogens are weak parasites. They can infect a plant only under stress conditions when its defences are lowered (Akhatov et al., 2013). The main risk factors:

• Cold and protracted spring — at low temperatures, germination slows down, and seedlings remain vulnerable longer.
• Waterlogged soil — excess moisture creates anaerobic conditions, roots suffocate, and pathogens gain advantage.
• Soil crust — it hinders air access to sprouts and mechanically damages tender stems.
• Deep seed placement — sprouts spend too much energy breaking through to the light and become weakened.
• Acidic soil reaction (pH < 5.5) — in acidic environments, many pathogens develop more actively, and plants absorb nutrients less well.
• Dense sowings — in crowded conditions, humidity is higher and ventilation at the soil surface is poorer.

How to Control Seedling Rot

Since seedling rot is caused by a complex of pathogens, control must be comprehensive and begin long before sowing.

1. Agronomic prevention

• Crop rotation (return beets to their original place no earlier than after 3–4 years). It is especially important not to sow beets after other root crops or crops affected by the same pathogens (carrots, potatoes).
• Liming of acid soils — bring pH to 6.0–6.5. This reduces the activity of many soil fungi and improves plant nutrition (Autko et al., 2012).
• Deep autumn ploughing (or digging) with turnover — incorporates plant residues and part of the pathogens into deep layers, where they survive less well.
• Optimal sowing time — when the soil warms up to +6…+8 °C at a depth of 5–6 cm. Do not sow in cold soil—seedlings will be weak and diseased.
• Do not thicken sowings — follow the recommended spacing (62+8 cm, 450–550 thousand plants/ha). Density worsens ventilation and increases humidity.
• Break the soil crust — by light harrowing across the rows or by sprinkler irrigation (75–100 m³/ha) (Autko et al., 2012).
• Destroy weeds from the Chenopodiaceae family (goosefoot, lamb’s quarters) — they are reservoirs of the pathogen Aphanomyces cochlioides (Akhatov et al., 2013).

2. Seed treatment

This is the most effective way to protect seedlings from seedling rot. Seed dressing with fungicides:

• TMTD (thiram) — 6–8 g per 1 kg of seeds (for a hobby garden — 6–8 g per 1 kg of seeds, or 1 tablespoon per 1 kg). This is a contact preparation that creates a protective screen on the seed surface.
• Maxim (fludioxonil) — effective against most seedling rot pathogens, suppresses seed moulding (Akhatov et al., 2013).
• Benlate (fundazol) — for treating seed plants before storage.
• In industrial scales, seed encrustation with protective‑stimulating compositions is used: fungicide + microelements (boron, manganese, zinc) + growth regulator (epin) (Autko et al., 2012).

Important: Treated seeds are stored for no more than one year—the effectiveness of treatment decreases over time.

3. Biological preparations

In organic farming, biopreparations based on antagonistic bacteria (e.g., Bacillus subtilis, Pseudomonas fluorescens) can be used. They are introduced into the soil or used for seed treatment. Their effectiveness is lower than chemical dressings, but combined with agronomy they give good results.

How to Recognise

• On the root collar and lower part of the stem, sunken dark‑brown or black spots (cankers) appear.
• Spots enlarge, constrict the stem, and the plant wilts.
• In wet weather, a cobweb‑like coating may be present on affected tissues.
• Adult plants are affected in the root collar area—rot penetrates inside the root, causing “pockets” of dry or wet rot.

Conditions for Development

• Rhizoctonia prefers warm (+25…+30 °C) and dry weather, unlike seedling rot, which develops in cold and waterlogged conditions.
• The fungus lives in the soil and affects a wide range of crops (potatoes, cabbage, tomatoes, cereals), so crop rotation is not always effective.

How to Control

• Preventive seed treatment with the same fungicides as for seedling rot (TMTD, Maxim).
• In industrial production, application of azoxystrobin (Quadris) into furrows at sowing and again at emergence significantly reduces losses from Rhizoctonia (Pethybridge et al., 2018). For a hobby garden, copper‑containing preparations can be used as soil drenches around plants.
• Improve drainage on heavy soils — growing on raised beds or ridges.
• Remove diseased plants together with a clump of soil to prevent spread of infection.

Fusarium Dry Rot

Pathogens: fungi of the genus Fusarium (mostly Fusarium oxysporum, F. solani).

How to recognise:

• Sunken, dry spots of dark‑brown or greyish colour appear on the root surface.
• On cutting, the affected tissue is dry, crumbly, often with cavities.
• The vessels of the root darken—this is a distinctive sign of Fusarium (Autko et al., 2012).
• Pinkish or white cushions of sporulation may form on the surface.
• Affected roots quickly turn into dry rot during storage, which can spread to neighbours.

Conditions for development:

• Hot and dry weather in the second half of summer weakens plants and makes them vulnerable.
• Mechanical damage during care or harvesting — entry points for infection.
• Potassium deficiency in the soil reduces tissue resistance.
• The fungus persists in soil and on plant residues for up to 3–5 years.

What to do:

• Crop rotation — do not plant beets after crops affected by Fusarium (potatoes, tomatoes, carrots), return no earlier than after 4 years.
• Destruction of plant residues — deep digging with incorporation of tops.
• Potassium fertilisation — potassium strengthens cell walls and increases resistance to Fusarium. Apply potassium sulphate or potassium magnesium (Balashev and Zeman, 1981).
• Nematode control — they damage roots, creating entry points for Fusarium.
• There is no chemical cure. Remove and destroy diseased roots.

Phoma Dry Rot

Pathogen: fungus Phoma betae (the same one that causes leaf spotting).

How to recognise:

• Dark‑grey, almost black, sunken spots appear on the root (Akhatov et al., 2013).
• The affected tissue on the cut is dark‑brown, dry, with clear boundaries.
• Small black dots—pycnidia of the fungus—are often visible on the surface of the spots.
• Rot often starts from the sides or the top of the root, not from the root collar (this distinguishes Phoma from Fusarium).
• During storage, affected areas become crumbly but remain dry (“dry rot”).

Conditions for development:

• Close association with boron deficiency — when boron is lacking, root tissues become loose, and Phoma easily penetrates inside (Autko et al., 2012).
• Cool and humid weather at the end of the growing season.
• Storage of infected mother roots—the fungus survives in them and infects seed plants in spring.

What to do:

• Boron application — a mandatory preventive measure. Use boric acid or borax as a foliar spray (1.5–3 kg/ha a.i., or 15–20 g per 10 L of water per 100 m²) at the 4–6 true leaf stage.
• Liming of acid soils — in acidic environments, boron is less available.
• Crop rotation and removal of diseased roots before storage.
• In industrial production, mother roots are treated with fundazol (2 kg/t) before storage (Akhatov et al., 2013).

Rhizomania (Root Bearding)

Pathogen: Beet necrotic yellow vein virus (BNYVV), transmitted by the soil‑borne fungus Polymyxa betae (Akhatov et al., 2013).

How to recognise:

• The root is small, with many interwoven lateral rootlets at the lower part (“beard”) (Akhatov et al., 2013).
• On the root section, blackened vessels are visible.
• Leaves are curled, veins yellowed or necrotic.
• Plants are stunted and lag in growth.
• The root is hard, fibrous, woody, inedible.

Especially dangerous information: the virus survives in the cysts of the vector fungus in the soil for more than 20 years! (Akhatov et al., 2013).

What to do:

• There is no cure. The only way is growing resistant varieties (in some regions there are varieties and hybrids with genetic resistance).
• Long crop rotation (at least 5–6 years) with crops not affected by the virus (cereals, legumes).
• Remove diseased plants together with roots and a clump of soil.
• Avoid growing beets on plots with a history of rhizomania.

Beet Mosaic and Yellowing

Pathogens: Beet mosaic virus, Beet yellow virus, Beet mild yellowing virus (Akhatov et al., 2013).

How to recognise:

• Mosaic: On leaves, mosaic light spots appear (round, stellate, reticulate), the leaf blade becomes wrinkled and thinner (Akhatov et al., 2013). Roots become smaller, quality declines.
• Yellowing: First, the tips of old leaves turn yellow, then yellowing spreads along the edges and between veins. Leaves become small, stiff, brittle, covered with necrotic spots (Autko et al., 2012). Root yield can drop by 25–65%, and seed yield by 40% or more.

Vectors: aphids (common beet aphid, black bean aphid) and other sucking insects.

What to do:

• No cure. Remove and destroy diseased plants.
• Aphid control is the main preventive measure. Apply insecticides (e.g., Bi‑58 New, Danadim Expert) when the first aphids appear (Akhatov et al., 2013). In a hobby garden, soap solution, tobacco or garlic infusion can be used.
• Destroy weed reservoirs (goosefoot, lamb’s quarters, sow thistle, amaranth) — viruses overwinter on them.
• Spatial isolation from old beet plantings (at least 1 km for seed plants).

Phoma Rot (Dry Black Rot)

Symptoms:

• Dark‑grey or black, slightly sunken spots appear on the root surface.
• Affected tissue becomes dry, hard, crumbly.
• Small black dots — pycnidia of the fungus — are visible on the spots (Autko et al., 2012).
• On cutting, dark‑brown, dry rot with clear boundaries is visible.

Features:

• Develops slowly, can remain latent for several months.
• Often starts from the top or sides of the root.

Prevention:

• Control Phoma in the field (see chapters 2 and 4).
• Boron application during the growing season.
• Thorough culling of roots with suspicious spots.

Grey Rot

Pathogen: Botrytis cinerea — a widespread fungus that affects many vegetables and fruits (Akhatov et al., 2013).

Symptoms:

• Watery, softened areas appear on the root surface.
• Over time, a fluffy grey coating (sporulation of the fungus) forms on them.
• Rot spreads quickly, especially at high humidity.
• Affected roots become soft, slimy.

Features:

• Develops at temperatures above +2 °C, especially actively at +15…+20 °C.
• Easily transmitted from diseased root to healthy one by contact.

Prevention:

• Optimal storage temperature (+1…+2 °C).
• Good ventilation.
• Prevent condensation on the root surface.

White Rot

Pathogen: Sclerotinia sclerotiorum — a fungus that affects more than 400 plant species (Akhatov et al., 2013).

Symptoms:

• A white, dense, cottony coating appears on the root.
• Inside the coating, black hard bodies (sclerotia) 2–10 mm in size are visible.
• Tissues under the coating soften and become watery.
• Rot quickly spreads to neighbouring roots.

Features:

• Very dangerous disease — can destroy up to 50% or more of the crop in storage.
• Sclerotia persist in the soil and on plant residues for 5–8 years.

Prevention:

• Thorough culling of suspicious roots.
• Disinfection of the storage facility before loading.
• Destruction of plant residues in the field.

Bacterial Wet Rot

Pathogens: bacteria of the genera Pectobacterium and Pseudomonas (Akhatov et al., 2013).

Symptoms:

• The root softens and becomes watery.
• Tissues turn into a slimy dark‑brown mass.
• A sharp, unpleasant putrid odour appears.
• Rot quickly transfers to neighbouring roots.

Features:

• Develops at elevated humidity and temperatures above +4 °C.
• Often starts from sites of mechanical damage.

Prevention:

• Careful harvesting and sorting.
• Avoid root injuries.
• Optimal storage conditions.

Preparation for Storage

2–3 weeks before harvest:

• Stop watering — excess moisture reduces storage ability.
• Inspect plantings — plants with signs of disease should be harvested earlier and used first.

At harvest:

• Harvest beets before frost. Even slight freezing (-1 °C) makes roots unsuitable for long‑term storage (Autko et al., 2012).
• Choose a dry day — wet roots store less well.
• Avoid mechanical damage. Cut the tops with a knife, do not break or twist them. Leave petioles no longer than 2 cm (Balashev and Zeman, 1981). If long petioles are left, they rot and infect the root.
• Do not wash roots before storage — moisture provokes rot. If roots are wet, they must be dried in a dry, ventilated place (but not in the sun, so they do not wilt).

Sorting:

This is the most important stage. Select for storage only:

• Healthy, without spots or cracks.
• Firm, elastic, without signs of wilting.
• Undamaged, without cuts or bruises.
• Typical for the variety in shape and colour.

Roots with the slightest suspicion (small cracks, suspicious spots) should be used for food first or processed.

Treatment before storage:

• In a hobby garden, roots can be dusted with chalk or wood ash — this dries the surface and suppresses the development of microorganisms.
• In industrial production, mother roots are treated with fungicides (fundazol, 5% solution) (Akhatov et al., 2013). For amateurs, biopreparations (Gamair, Fitosporin‑M) can be used as spraying.

Optimal Storage Conditions

Creating the right microclimate is the key to successful storage.

Important: There should be no sharp fluctuations in temperature and humidity in the storage. When walls cool, condensation may form, which drips onto the roots and provokes rots.

Storage Methods for the Gardener

In a cellar or basement:

• The best way is storage in containers or boxes with slits for ventilation.
• Roots can be layered no more than 1 m high.
• Layers can be interlaid with moist sand (but not wet!) or sawdust — this maintains humidity and prevents contact between roots (Karataev and Sovetkina, 1984).
• Do not place boxes tightly against walls — leave a gap of 5–10 cm for air circulation.

In trenches or clamps (for large volumes):

• In regions with mild winters, roots can be stored in trenches 50–60 cm wide and 70–80 cm deep (for carrots) or 70–80 cm (for beets) (Balashev and Zeman, 1981).
• Roots are placed in the trench, interlaid with sand, covered with straw and a 20–30 cm layer of earth on top.
• As it gets colder, the covering is increased.

In plastic bags:

• Research has shown that carrots are best preserved in open plastic bags of 35–50 kg (Balashev and Zeman, 1981). Inside the bag, increased humidity and accumulation of carbon dioxide (up to 3–5%) are created, which suppresses putrefactive bacteria. Beets also store well this way.
• Important: bags should be left open to allow gas exchange. When stored in completely sealed plastic bags, roots suffocate and rot.