Sclerotial or white rot

Sclerotial or white rot (sclerotinia sclerotiorum) is a fungal disease affecting a wide range of agricultural, ornamental, and forest plants. White rot is one of the most destructive diseases, causing significant losses in agriculture, particularly in crops such as sunflower, soybean, tomatoes, beans, cabbage, as well as in garden plants and flowers. The disease is characterized by rapid development and severe damage to plant tissues, leading to their decay. Sclerotial rot causes the rotting of stems, roots, fruits, and flowers, leading to a substantial decrease in yield and quality of the produce.

Article objectives:

The purpose of this article is to provide comprehensive information on white rot, including its symptoms, causes, diagnostic methods, and treatment. After reading the article, the reader will learn to:

• recognize the signs of white rot.
• understand the factors contributing to the disease's development.
• properly diagnose white rot and distinguish it from other diseases.
• use effective control methods for this disease.
• implement preventive measures to reduce the risk of infection.

Symptoms and signs of the disease

Symptoms of white rot manifest on various parts of the plant, including roots, stems, leaves, flowers, and fruits. The disease typically starts from the lower parts of the plant and gradually spreads upwards.

1. Root and stem base infection:
   • white rot often begins with the infection of roots, especially in plants grown in overmoisturized soil or poor drainage conditions. Water-soaked spots appear on the infected areas, which quickly enlarge.
   • soft, water-soaked lesions develop on the roots and at the base of the stem, which may turn into necrosis. These areas may become white and covered with a powdery mildew-like layer, characteristic of white rot.
2. Stem and shoot infection:
   • water-soaked spots appear on the stems, which become soft and easily disintegrate over time. These areas are covered with the white mycelium of the fungus.
   • on the affected areas, characteristic white masses of mycelium appear, which then begin to darken. The fungus can penetrate the vascular system of the plant, disrupting transpiration and water supply.
   • eventually, stems break and die, and the plant loses its stability.
3. Flower and fruit infection:
   • in cases where flowers are infected, they lose their form, become watery, soft, and then begin to rot. The flowers turn into gray or brown masses, where sclerotia (hard fungal bodies) form.
   • on fruits, such as tomatoes, sunflower, cabbage, or beans, water-soaked spots also appear, which gradually turn into decay. The fruits become soft, covered with white mycelium, and decompose.
   • fruits and seeds infected by white rot lose their quality and become unsuitable for sale or processing.
4. Sclerotia formation:
   • in later stages of the disease, sclerotia — black or dark brown structures — may form on the affected parts of the plant, which serve as sources of infection in subsequent years. These sclerotia are often found inside decomposing plant tissues but can also be visible on the surface.
5. General wilting of the plant:
   • in cases of intense white rot infection, plants quickly wilt, lose turgor, leaves turn yellow, and the roots and stems decompose. This leads to plant death.

Etiology of white rot

The pathogen of white rot is the fungus sclerotinia sclerotiorum, belonging to the genus sclerotinia (family sclerotiniaceae). This is one of the most aggressive pathogens, with a wide host range. The fungus can infect more than 400 species of plants, including many agricultural crops, ornamental plants, and even forest plants.

The main feature of sclerotinia sclerotiorum is its ability to form sclerotia — specialized structures that can survive in soil and plant residues for extended periods (up to several years). These structures are hard, black or dark brown formations, which help the fungus survive in unfavorable conditions. When conditions become favorable for growth (humid and warm environments), the sclerotia germinate, forming new infectious structures — ascospores and mycelium.

Life cycle of white rot

The life cycle of sclerotinia sclerotiorum is complex and includes several key stages:

1. Sclerotia germination: the fungus can survive as sclerotia in soil and plant residues in unfavorable conditions. When favorable conditions (humidity, warmth) occur, the sclerotia begin to germinate, forming mycelium that penetrates plant tissues.
2. Infection process: the ascospores, formed during the germination of sclerotia, spread through the wind or water and land on plants, infecting them. Spores penetrate plant tissues through damage or natural openings, such as stomata.
3. Mycelium development: the mycelium develops inside plant tissues, destroying cell walls and absorbing nutrients. This causes decay and death of plant tissues.
4. Formation of new sclerotia: after the fungus decomposes plant tissues, new sclerotia form on the plant's surface, which can remain in the soil and continue to infect plants in the future.
5. Disease persistence: sclerotia can survive for long periods in the soil and plant residues, making infection possible in subsequent seasons. This promotes disease spread and pathogen accumulation.

Conditions for white rot development

White rot develops under specific climatic and soil conditions:

1. High humidity: the fungus sclerotinia sclerotiorum prefers a humid environment, where its spores can actively germinate. Prolonged rain, fog, and high air humidity are particularly dangerous.
2. Temperature: the optimal temperature for disease development is 18-24°c, although the fungus can grow at higher temperatures. However, temperatures above 30°c may slow disease progression.
3. Poor ventilation: dense plantings and poor air circulation create moist conditions that favor the development of white rot.
4. Low drainage: overmoisturized soil and poor drainage create favorable conditions for sclerotia survival in the soil and root infection.
5. Plant damage: mechanical damage, pests, or other diseases may weaken plants and allow fungi to penetrate plant tissues.

Improper care:

• excessive or insufficient watering: overwatering leads to soil saturation, creating ideal conditions for fungal growth. Insufficient watering weakens the plant, reducing its immunity.
• improper lighting: lack of light reduces plant photosynthetic activity, weakening its immune system, while excessive lighting may cause thermal damage.

Environmental conditions:

• high humidity or dryness: high humidity promotes fungal growth, while dry conditions weaken plants, making them more vulnerable.
• temperature fluctuations: sharp temperature fluctuations, especially at night, create stress for the plant, contributing to disease development.

Poor sanitation:

• contaminated tools and pots: using non-sterile tools or contaminated pots may transfer the fungus from one plant to another.
• frequent plant movement: moving plants frequently may stress them and increase the likelihood of infection.

Plant stress conditions:

• overwatering, drying, intense lighting, or nutrient deficiency: all of these conditions create stress for the plant, weakening its immune system and increasing susceptibility to diseases.

Diagnosis of plant diseases

1. Visual inspection

The primary method for diagnosing white rot is visual inspection of plants. Symptoms can vary depending on the development stage and type of affected plant. The most characteristic signs include:

• stem and root rot: on infected stem or root areas, white, fluffy mycelial growths appear. Over time, decay spreads and destroys plant tissues. Soft, wet rot may form on the stems.
• sclerotia formation: in advanced stages of the disease, hard black or brown formations called sclerotia may appear on the affected parts of the plant (stems, roots, flowers), structures where the fungus survives in unfavorable conditions.
• fruit rot: fruits, especially in greenhouses or on plants with high humidity, begin to rot, covered with white mycelium. The decaying parts lose their shape and become soft, often with an unpleasant odor.
• general wilting: plants with white rot often begin to wilt, losing turgor, and the leaves and stems become soft and watery.

2. Microscopic examination

To confirm the diagnosis, microscopy can be used. Microscopic examination helps identify characteristic features of the fungus:

• fungus mycelium: white rot is accompanied by the spread of white mycelium, which can be observed under the microscope on infected plant tissues. The mycelium is often fluffy and loose, covering affected areas.
• sclerotia: under the microscope, sclerotia can be observed, which are typically black or brown in color. These formations are important diagnostic signs.

3. Laboratory research

For accurate diagnosis and confirmation of the presence of sclerotinia fungi, laboratory methods can be employed, such as:

• fungal culturing: in the laboratory, the fungus can be isolated from infected plant tissues (stems, roots, fruits) and cultured on nutrient media. This helps confirm the fungal species causing the disease.
• PCR method: polymerase chain reaction (pcr) can be used to identify the fungus dna in infected plants. This is especially effective in the early stages of the disease when visual symptoms may be weak.

4. Differential diagnosis

It is important to perform differential diagnosis to distinguish white rot from other diseases with similar symptoms:

• root rot: white rot differs from root rot in that it forms a characteristic white, fluffy growth on the plant's surface.
• fusarium wilt: fusarium causes rot, but the plant develops not white growths, but pink, red, or orange spots. Yellowing and wilting are also more pronounced in fusarium.
• bacterial infections: bacterial infections cause wet spots on leaves and stems, which have a more watery texture, unlike white rot, which is characterized by web-like growth and leads to tissue death.

Thus, the diagnosis of white rot involves visual inspection, microscopic studies, laboratory methods, and differential diagnosis to exclude other diseases with similar symptoms. The earlier the diagnosis, the easier it will be to combat the disease and minimize its spread.

Treatment of sclerotial (white) rot in plants

The treatment of sclerotial rot requires a comprehensive approach, including the use of chemical agents, biological methods, agronomic practices, and improvement of growing conditions. White rot is a dangerous disease that can spread quickly, causing significant damage to plants if timely measures are not taken. Here are some effective methods to control white rot:

1. Use of fungicides

Fungicides are the primary means of controlling white rot, as they help control fungal development and prevent its spread to healthy parts of the plant.

• contact fungicides: these preparations act on the fungal infection on the plant's surface. Examples:
  • Copper-based preparations (such as copper sulfate, bordeaux mixture) — effective in the early stages of the disease.
  • Sulfur and sulfur-containing preparations — help prevent further spread of the disease.
• systemic fungicides: these preparations penetrate the plant's tissues, providing internal protection. They are effective for deeper infections and are more resistant to rain and moisture. Examples:
  • Triazoles (such as topsin-m) — help control fungal development inside the plant  and prevent the spread of infection through vascular tissues.
  • Strobilurins (such as fundazole) — effective against a wide range of fungal diseases, including sclerotial rot.

Application of fungicides:

• apply fungicides as soon as the first signs of the disease appear.
• repeat treatment every 7-14 days, depending on the extent of infection and the selected product.
• it is important to follow the dosage and instructions on the package to avoid overdosing and plant damage.

2. Removal of affected plant parts

If sclerotial rot has already spread to leaves, stems, fruits, or roots, it is important to remove all affected parts of the plant. This will help stop further spread of the fungus and reduce the risk of infecting other plants.

Removal stages:

• inspect the plant and carefully trim all infected parts, including leaves, fruits, and stems.
• use sterile tools (such as pruning shears or scissors) to minimize mechanical damage to healthy plant parts.
• dispose of infected plant parts properly: burn them or dispose of them in sealed bags to prevent the spread of fungal spores in the soil and to other plants.

3. Correction of growing conditions

White rot develops in conditions of high humidity and poor ventilation, so improving growing conditions helps prevent the spread of the disease and supports plant health.

• ventilation: provide good air circulation around the plants, especially in greenhouses and enclosed spaces. This will reduce humidity and prevent moisture buildup on leaves and stems.
• watering: water the plants at the root, avoiding water on leaves and stems to prevent creating favorable conditions for fungal growth.
• removal of plant residues: remove plant residues, especially those affected by rot, as they can serve as a source of infection for future plants.

4. Use of biological agents

Biological fungicides can be used to control white rot, providing a safe alternative to chemical products and helping reduce the spread of the disease.
Examples of biological agents:

• trichoderma — a fungus that suppresses the growth of sclerotinia and other pathogens.
• bacillus subtilis and bacillus amyloliquefaciens — microorganisms with antiseptic properties that help protect plants from white rot and other fungal infections.

5. Fertilizing plants

After being infected with white rot, plants weaken, so it is necessary to provide them with additional nutrients for faster recovery.

• nitrogen fertilizers — help speed up growth recovery, but avoid overdosing to prevent excessive green mass growth, which can weaken the plant.
• phosphorus-potassium fertilizers — strengthen the root system and increase plant resistance to diseases.

6. Use of resistant varieties

Using plant varieties resistant to white rot helps minimize future damage from the infection. Varieties resistant to this disease significantly reduce the likelihood of infection.

7. Tool sterilization

Regularly clean and disinfect garden tools and equipment, such as pruning shears, scissors, shovels, and others, to prevent the spread of infection from one plant to another.

Treatment of white rot requires a comprehensive approach, involving both chemical and biological agents, improving growing conditions, and removing infected plant parts. It is important to identify the disease promptly and take measures to prevent and treat it to minimize damage and preserve plant health.

Prevention of sclerotial (white) rot in plants

Prevention of sclerotial rot focuses on creating conditions that inhibit the development and spread of the fungus, as well as implementing measures to reduce the risk of plant infection. The main goal of preventive measures is to minimize the factors that contribute to pathogen spread.

1. Choosing resistant varieties

One of the most effective methods of preventing white rot is using plant varieties resistant to the disease. Modern varieties are often more resistant to fungal diseases, including sclerotial rot. When purchasing planting material, it is important to focus on varieties that have enhanced resistance to this disease, significantly reducing the likelihood of infection.

2. Crop rotation

Crop rotation is an important practice to prevent pathogen buildup in the soil. White rot can survive in plant residues and soil for extended periods, and if plants susceptible to the disease are grown in the same location for several years, the risk of infection increases. Regular crop rotation helps reduce fungal concentration in the soil and lowers the risk of re-infection.

3. Managing plant residues

It is important to remove all plant residues, especially those infected by white rot, to prevent overwintering and pathogen spread. Leaves, stems, and fruits left in the field can serve as sources of infection, providing the pathogen with a medium for survival and spread.

Recommendations for managing plant residues:

• collect and destroy all plant residues, for example, by burning or disposing of them in sealed bags.
• do not leave infected plant parts in compost piles, as they can become a source of further disease spread.

4. Optimizing growing conditions

White rot develops in conditions of high humidity and poor ventilation, so creating optimal conditions for plants plays a key role in disease prevention.

Ventilation:

• ensure good air circulation around plants, especially in greenhouses, to prevent moisture buildup.
• regularly ventilate greenhouses and other enclosed spaces.

Watering:

• water plants at the root, avoiding water on leaves and stems to prevent creating favorable conditions for the fungus.
• drip irrigation helps maintain optimal soil moisture levels without creating conditions for fungal growth.

Mulching:

• mulching helps maintain stable soil moisture, preventing overheating or rapid drying.
• it promotes healthy root development and reduces the risk of fungal infections.

5. Regular plant inspection

Constant monitoring of plant conditions allows early detection of white rot. This is important for timely disease control and preventing its spread.

Inspection recommendations:

• regularly check plants for signs of rot, such as spots on leaves, water-soaked areas on stems, or fruits that have become soft and deformed.
• when the first signs of infection appear (e.g., brown or gray spots), immediately remove the affected parts of the plant to prevent the spread of infection.

6. Use of fungicides for prevention

Preventive fungicide treatments help prevent white rot infection before the disease manifests. Fungicides applied at early stages of the growing season, especially under conditions of increased humidity and rain, significantly reduce the risk of the disease.

Examples of fungicides:

• contact fungicides: copper-based preparations (such as copper sulfate or bordeaux mixture) effectively protect plants from fungal diseases and are used for white rot prevention.
• systemic fungicides: preparations such as ridomil gold and topsin-m penetrate plant tissues and provide long-term protection against the disease.

7. Use of biological protection methods

To enhance plant resistance and minimize the impact of chemical substances, biological fungicides can be used. These preparations are environmentally safe and suitable for organic farming.

Examples of biological preparations:

• trichoderma — a fungus that suppresses the growth of white rot and other pathogens.
• bacillus subtilis and bacillus amyloliquefaciens — microorganisms with antiseptic properties that help protect plants from white rot and other fungal infections.

8. Tool and equipment sterilization

To prevent the spread of the pathogen between plants, it is important to regularly clean and disinfect gardening tools and equipment, such as pruning shears, scissors, shovels, and others. This helps prevent mechanical spread of infection and minimize the likelihood of infection.

9. Soil sterilization

Before planting new plants, it is essential to sterilize the soil, especially if it has been used for plants infected with white rot. This helps prevent pathogen spread in the soil and reduces the risk of disease.

Prevention of white rot in plants requires a comprehensive approach, including proper plant care, the use of resistant varieties, adherence to crop rotation, creating optimal growing conditions, and the application of both chemical and biological agents. Regular inspections and preventive treatments will help protect plants from white rot and other diseases.

Care for infected plants

Isolating infected plants:

• separate infected plants from healthy ones to prevent pest spread. This helps minimize the risk of infecting other plants.

Trimming and removing affected parts:

• carefully remove infected leaves, stems, and roots: this will allow the plant to focus resources on healthy parts and increase the chances of recovery.

Plant treatment:

• use appropriate means to combat pests and pathogens: treat plants with fungicides or organic agents depending on the disease stage.

Recovery after illness:

• regular watering, fertilization, and ensuring optimal conditions for plant recovery: maintain a balance of water, nutrients, and lighting.

Specific recommendations for different types of plants

Flowering plants (orchids, geraniums, philodendrons):

• the care for these plants involves maintaining optimal humidity and temperature levels, preventing water stagnation, and regular inspection for fungal diseases.
• flowering plants are particularly susceptible to fungal infections, so they require extra attention to avoid conditions like excessive humidity, which can promote white rot.

Green leafy plants (pachira, sansevieria, zamioculcas):

• these plants are generally more resistant to white rot but still require careful care, especially in high humidity conditions.
• avoid overwatering, and ensure proper drainage to prevent waterlogging, which can create a conducive environment for fungal growth.

Succulents and cacti:

• succulents are less prone to white rot, but they can become infected if they are overwatered or exposed to excessive moisture.
• these plants prefer drier conditions, and watering should be done sparingly, allowing the soil to dry out between watering sessions.

Tropical plants (spathiphyllum, ficus benjamin):

• tropical plants require special conditions to prevent white rot, including maintaining optimal climatic conditions, avoiding waterlogging, and regular prevention treatments.
• these plants thrive in humid environments, but care should be taken to ensure that the humidity is not excessive and that the soil is well-drained.

Professional help and consultations

When to consult specialists:

• if the symptoms of the disease progress and home methods are not effective, it is important to consult a specialist for accurate diagnosis and treatment recommendations.
• consulting a professional is especially crucial if the plant is valuable or has sentimental importance.

Types of services offered by specialists:

• specialists can provide diagnostics, plant treatment, and advice on plant care and disease prevention.
• they can also help with more advanced treatments or identify potential issues before they spread.

Choosing a specialist:

• when selecting a specialist, it is important to consider their qualifications and experience. It is recommended to consult certified agronomists or phytopathologists with positive reviews and proven expertise in plant health management.

Conclusion

Summary:

• white rot is a serious fungal disease that requires careful attention and timely intervention. Understanding the causes, symptoms, and control methods helps effectively protect plants from damage.
• regular care and monitoring are crucial in preventing and managing white rot, as early detection significantly increases the chances of successful treatment.

The importance of regular care and monitoring:

• regularly checking the condition of plants and providing proper care can help prevent the onset and spread of diseases.
• implementing best practices in plant care, such as optimizing watering, lighting, and ventilation, will ensure healthier plants that are more resilient to diseases like white rot.

Motivation for action:

• use the knowledge gained from this article to maintain the health of your plants and prevent them from becoming infected with white rot. Taking early action can prevent significant damage and maintain the aesthetic and functional value of your plants.

Frequently asked questions (FAQ)

Sclerotinia rot is a fungal disease caused by the pathogen sclerotinia sclerotiorum. It is a one-year parasite that affects a wide range of crops, including cabbage, beans, sunflowers, soybeans, peas, and many others. The disease is characterized by the formation of white mycelial films on affected parts of the plant and the development of sclerotia — hard structures that allow the fungus to survive in unfavorable conditions.

1. Which plants are most susceptible to sclerotinia rot?

Sclerotinia rot affects over 400 plant species, including:

• Cabbage and other cruciferous crops
• Sunflowers
• Beans and peas
• Soybeans
• Carrots
• Onions
• Tomatoes
• Cucumbers
• Berries (e.g., strawberries)

The variety of crops affected makes sclerotinia rot a serious threat to agricultural production.

2. What are the main symptoms of sclerotinia rot?

The main symptoms include:

• White fluffy mycelium on leaves, stems, and fruits.
• Brown or black sclerotia visible on the surface of the affected tissues.
• Tissue death and wilting of plants.
• The appearance of watery spots on the leaves.
• Root and stem rot in severe cases.

Early diagnosis allows for the implementation of control measures.

3. How does sclerotinia rot spread?

Sclerotinia rot spreads through:

• Sclerotia: hard structures capable of carrying the fungus over long distances through wind, water, or mechanical means.
• Spores: moist conditions promote spore formation, which spreads through the air.
• Infected plant residues: fallen leaves and other organic materials serve as a source of infection for the next season.

Wet weather and high humidity promote the faster spread of the disease.

4. What conditions promote the development of sclerotinia rot?

The development of sclerotinia rot is stimulated by the following factors:

• High humidity and prolonged rainfall.
• Temperatures between 15°c and 25°c, optimal for fungal growth.
• Dense plantings that increase humidity within the canopy.
• Poor agricultural practices, such as inadequate drainage and excessive irrigation.
• Presence of infected plant residues in the field.

Controlling these factors helps reduce the risk of infection.

5. How to diagnose sclerotinia rot in plants?

Diagnosis is based on visual inspection and includes:

• Observation of white mycelial covering and sclerotia on affected parts of the plant.
• Analysis of symptoms such as wilting and tissue rot.
• Laboratory methods, including microscopy and cultural plating to confirm the presence of sclerotinia sclerotiorum.

Early diagnosis allows for effective control of disease spread.

6. What preventive measures exist for sclerotinia rot?

Main preventive measures include:

• Crop rotation: alternating crops that are not susceptible to the disease helps reduce the accumulation of the pathogen in the soil.
• Removal of plant residues: destroying fallen leaves and other organic materials reduces the source of infection.
• Selecting resistant varieties: planting varieties that are less susceptible to sclerotinia rot.
• Optimizing agricultural practices: proper watering, ensuring good drainage, and adequate ventilation.
• Using mulch: reduces disease outbreaks by retaining moisture and preventing spores from reaching plants.

Combining these measures ensures effective disease prevention.

7. How to treat sclerotinia rot in plants?

Treatment involves a comprehensive approach:

• Fungicides: use of chemical or biological fungicides to control the fungus. It is important to follow dosage and application time recommendations.
• Removal of affected parts: removing and destroying infected leaves, stems, and fruits.
• Optimizing agricultural practices: improving drainage, reducing planting density, and ensuring adequate ventilation.
• Biological methods: using microbial preparations that compete with the fungus.

Early and timely treatment minimizes damage from the disease.

8. Can organic methods be used to combat sclerotinia rot?

Yes, organic methods include:

• Biological fungicides: products based on microorganisms that suppress the growth of sclerotinia sclerotiorum.
• Absorbents and natural extracts: some plant extracts have fungicidal properties.
• Crop rotation and mulching: reduces the population of the pathogen in the soil.
• Composting: high temperatures during composting destroy sclerotia.

Organic methods can be effective when combined with other control measures.

9. How does sclerotinia rot affect crop yield and fruit quality?

Sclerotinia rot significantly reduces crop yield and fruit quality:

• Yield loss: fruit decay makes them unsuitable for sale or consumption.
• Decreased quality: affected plants lose their ornamental and nutritional value.
• Weakened plants: wilting and tissue decay weaken plants, making them vulnerable to other diseases and pests.
• Economic losses: decreased yield and quality lead to financial losses for farmers.

Effective control of sclerotinia rot is important for maintaining crop yield and quality.

This concludes the guide on white rot. Regular monitoring, proper care, and timely intervention are the keys to keeping plants healthy and preventing the spread of this destructive disease.