Crown Rot

What is Crown Rot?

Crown rot is a generic term referring to a condition in plants wherein the “crown” – the part of the plant where the stem meets the root, usually at or near the soil surface – becomes infected by a pathogen, leading to decay. The infection typically causes the tissue to rot, becoming soft, brown, and often emitting a foul odor.

Regions Impacted

Crown rot is a global problem, prevalent in regions with:

• High humidity or prolonged wet conditions.
• Poorly drained soils.
• Overhead irrigation systems that keep plant crowns wet for extended periods.

What Causes Crown Rot?

Crown rot can be caused by a range of pathogens, but fungi are the most common culprits. Notable fungi include those from the genera Phytophthora, Rhizoctonia, Fusarium, and Sclerotinia. There are also bacterial pathogens that can induce crown rot.

What are the Different Types of Crown Rot?

Here are some of the main types of crown rot:

• Phytophthora Crown Rot:
  • Causal Agent: Fungi from the genus Phytophthora.
  • Symptoms: Water-soaked spots on the crown that expand and girdle the stem. The plant may wilt, and roots may become discolored and rotten.
  • Host Plants: Affects a wide range of plants including fruit trees, ornamentals, and vegetables.
• Rhizoctonia Crown Rot:
  • Causal Agent: Fungus Rhizoctonia solani.
  • Symptoms: Dry, brown cankers on the crown. Roots may also rot.
  • Host Plants: Primarily affects vegetables and some ornamentals.
• Sclerotinia Crown Rot (White Mold):
  • Causal Agent: Fungus Sclerotinia sclerotiorum.
  • Symptoms: Water-soaked lesions on the crown, often accompanied by white, cottony fungal growth. Hard black structures (sclerotia) may form.
  • Host Plants: Many vegetables, legumes, and some ornamentals.
• Fusarium Crown Rot:
  • Causal Agent: Fungi from the genus Fusarium.
  • Symptoms: Reddish-brown cankers form at the soil line. The disease may move down into the roots or up into the stem.
  • Host Plants: Several, including tulips, lilies, and some grasses.
• Southern Blight (also sometimes referred to as Crown Rot):
  • Causal Agent: Fungus Sclerotium rolfsii.
  • Symptoms: White, cottony fungal growth around the base of the plant, with small, round, tan to brown sclerotia.
  • Host Plants: A very wide range of plants including vegetables, ornamentals, and field crops.
• Bacterial Crown Rot:
  • Causal Agent: Various bacterial pathogens.
  • Symptoms: The crown becomes slimy and emits a foul odor. The plant may become stunted and wilt.
  • Host Plants: Various, depending on the bacterial species involved.

Prevention and control of crown rot diseases often involve practicing good sanitation, rotating crops, ensuring proper drainage, and using disease-free planting materials. Fungicides can be effective in some cases, but it’s essential to correctly identify the disease and choose an appropriate product.

What are the Symptoms?

Symptoms of crown rot vary depending on the causative pathogen but generally include the following:

• Wilting or yellowing of leaves, especially during the hottest part of the day.
• Browning or blackening at the base of the stem.
• Rotting of roots, which might be brown and mushy.
• Stunted growth.
• Dark brown to black lesions on the crown.
• Under severe infections, the whole plant may die.

How to Control Crown Rot?

• Soil Management: Ensure good drainage in planting areas. Raised beds can be beneficial for plants susceptible to crown rot.
• Crop rotation: Avoid planting the same crop in the same location for consecutive years.
• Sanitation: Regularly remove plant debris. Sterilize tools and avoid working in the garden when plants are wet.
• Resistant Varieties: Some plant varieties have been bred to be more resistant to crown rot.
• Proper Watering: Use soaker hoses or drip irrigation instead of overhead watering. Water in the morning so that plants have time to dry out during the day.
• Biological Control: Beneficial fungi can compete with the pathogens, reducing their numbers.
• Chemical Control: Fungicides can be used, but it’s essential to choose a product labeled effective against crown rot and to follow the label directions carefully.
• Soil Solarization: Before planting, cover the soil with clear plastic during the hottest months. This will heat the soil and can kill many soil-borne pathogens.

Crown rot is a widespread and often severe plant disease caused by a variety of pathogens. While challenging to control once established, preventive measures can significantly reduce its impact. Proper garden hygiene, combined with suitable cultural practices, can keep this devastating disease at bay.