Drop (Sclerotinia Rot)

Lettuce DropLettuce Drop

Sclerotia on infected lettuceSclerotia on infected lettuce.

Soft, rotted tissueSoft, rotted crown tissue. 

Field with infected lettuceField of infected lettuce.

HOSTS

  • Leafy Greens

DESCRIPTION

Sclerotinia rot is caused by Sclerotinia sclerotiorum, a fungal pathogen. S. sclerotiorum affects a wide range of hosts, including root crops, legumes, and solanaceous crops however, “drop” is specific to lettuce. 

BIOLOGY

S. sclerotiorum produces hard, black structures called sclerotia during late summer and early fall. The sclerotia can survive dormant in the soil for extended periods. When conditions are wet and cool, optimally 60 °F to 70 °F, the sclerotia will produce fruiting bodies which release spores. The spores are spread by wind and water to new hosts. Infection can occurs when roots or leaves of susceptible plants come into contact with the sclerotia, mycelium or spores of the pathogen. The fungus can also survive on plant debris when host plants are not available. 

SYMPTOMS

  • Brown and yellow discoloration of leaves. 
  • Watery rot of the crown and stem of the host plant.
  • Abrupt wilting or “drop” of leaves.  
  • Hard, dark structures that develop on and within infected plant tissue. 

GENERAL MANAGEMENT

  • Remove and dispose of infected plants.  
  • Manage weeds as they can serve as alternative hosts for the disease. 
  • Minimize moisture on plants by utilizing drip irrigation and providing space between crops for ventilation. 
  • Rotate with nonsusceptible crops such as grains or corn to reduce disease build-up. 
Precautionary Statement: Utah State University and its employees are not responsible for the use, misuse, or damage caused by application or misapplication of products or information mentioned in this document. All pesticides are labeled with ingredients, instructions, and risks, and not all are registered for edible crops. “Restricted use” pesticides may only be applied by a licensed applicator. The pesticide applicator is legally responsible for proper use. USU makes no endorsement of the products listed in this publication.