Southern blight
Sclerotium rolfsii
What is Southern blight (Sclerotium rolfsii)?
Southern blight, caused by the fungus Sclerotium rolfsii, has a wide distribution and affects various fields, vegetables, and ornamental crops. It is particularly prevalent in warm and moist regions. Infected plants show symptoms at the soil line or below ground, including discolored crown/stem lesions, wilting, lower leaf discoloration, plant collapse, and death. These sclerotia resemble mustard seeds in size and color and serve as the primary diagnostic feature of the disease.
How does Southern blight (Sclerotium rolfsii) occur?
Southern blight reproduces through the production of sclerotia, which are small, tan to brown, round structures formed by the mycelia of the Sclerotium rolfsii fungus. These sclerotia serve as survival structures in the soil and can remain dormant for extended periods. When favorable conditions are present, the sclerotia germinate, and the fungus produces white hyphae or mycelia, which infect plant tissues at the soil line or below ground. The fungus can also spread through infected planting materials, such as bulbs or rhizomes, contributing to its dissemination and establishment in new locations.
Symptoms
1 - Impact on Plants
• Basal Stem Rot: Sclerotium rolfsii infects the base of plants, causing rotting and decay of stems, leading to wilting, plant collapse, and eventual death. • Root Rot: The fungus attacks plant roots, impairing their ability to uptake water and nutrients, resulting in stunted growth, yellowing of leaves, and overall decline.
2 - Effects on Soil
• Persistent Survival Structures: Sclerotia produced by the fungus persist in the soil, serving as a source of future infections, even over multiple growing seasons. • Reduction in Soil Health: Continuous presence of the pathogen can lead to a decline in soil quality and fertility, impacting overall plant growth and productivity.
3 - Environmental Impact
• Spread and Contamination: Southern blight can spread through contaminated soil, infected plant debris, or water, potentially affecting neighboring fields, gardens, or natural areas. • Economic Losses: The disease can result in significant economic losses for crops, horticultural industries, and nurseries.
Solutions
1 - Crop Management
• Practice crop rotation by avoiding consecutive plantings of susceptible crops in the same area. • Rotate with non-host crops to break the disease cycle and reduce the buildup of the pathogen in the soil.
2 - Sanitation and Debris Management
• Remove and destroy infected plant debris, including roots and stems, to prevent the spread of the pathogen. • Properly dispose of the debris to reduce the presence of the fungus in the growing area. • Avoid overwatering, as excessive soil moisture creates favorable conditions for Southern blight. • Implement proper irrigation techniques to maintain appropriate soil moisture levels for plant health.
3 - Healthy Plant Practices
• Use disease-free planting material and inspect bulbs, rhizomes, or other stock for signs of disease before planting. • Maintain balanced plant nutrition to enhance plant vigor and resistance to diseases. • Avoid excessive nitrogen fertilizer, as it can promote lush growth and increase plant susceptibility to Southern blight.
4 - Chemical Control
• Tebuconazole (e.g., Torque): Apply as a foliar spray. • Cyprodinil/Fludioxonil (e.g., Palladium): Apply using recommended rates. • Flutolanil (e.g., Prostar 70 WG): Apply according to label instructions. • PCNB (e.g., Terraclor 400): Incorporate into the top 2 inches of soil. • Always follow label instructions and consult local authorities for specific recommendations.
