This article is provided by theUW Plant Disease Diagnostics Clinic.
What is bacterial soft rot?
Bacterial soft rot describes a group of diseases that cause more crop loss worldwide than any other bacterial disease. Bacterial soft rots damage succulent plant parts such as fruits, tubers, stems and bulbs of plants in nearly every plant family. Soft rots commonly affect vegetables such as potato, carrot, tomato, cucurbits (e.g., cucumbers, melons, squash, pumpkins), and cruciferous crops (e.g., cabbage, cauliflower, bok choy). These diseases can occur on crops in the field as well as on harvested crops in storage. Rot can occur over a wide temperature range (with the worst decay between 70 and 80°F) and is particularly severe when oxygen is limited.
What does bacterial soft rot look like?
Soft rot bacteria degrade pectate molecules that bind plant cells together, thus causing plant structure to fall apart. Woody tissues are not susceptible. Initially, bacterial soft rots cause water-soaked spots. These spots enlarge over time and become sunken and soft. Interior tissues beneath the spots become mushy and discolored, with the discoloration ranging anywhere from cream to black. Seepage from affected areas is common. Soft rots are known for a strong, disagreeable odor that accompanies the breakdown of plant tissue.
Where does bacterial soft rot come from?
Soft rots are caused by several bacteria, most commonly species ofPectobacterium[particularlyPectobacterium carotovorum(previously calledErwinia carotovora)],Dickeyaspecies [particularlyDickeya dadantii(previously calledErwinia chrysanthemi)], and certain species ofPseudomonas,BacillusandClostridium. These bacteria can enter plants through wounds caused by tools, insects, and severe weather such as hail, as well as through natural openings. The bacteria can be spread from plant to plant by insects, on contaminated tools, or by movement of infested plant debris, soil, or contaminated water. Bacterial soft rots tend to be more of a problem during wet weather and can be more severe when plants lack sufficient calcium.
How do I save a plant with bacterial soft rot?
Once soft rot bacteria have infected plant tissue, there are no treatments. Immediately remove and discard infected plants or plant parts. DO NOT bury or compost this material.
How do I avoid problems with bacterial soft rot in the future?
Avoiding wet conditions is key for managing soft rot. Plant vegetables in well- drained soils, and control watering times and amounts, making sure plants are watered adequately (but not excessively) and uniformly. DO NOT crowd plants; wider spacing will promote more rapid drying of plants and soil. Make sure that soil fertility (particularly soil calcium) is optimal for the vegetables that you are growing based on a soil nutrient test. Add calcium (e.g., bone meal) at planting as needed.
Use soft rot-resistant vegetables in rotation with susceptible vegetables. Corn, snap beans and beets are vegetables that are not considered susceptible to soft rot. When growing broccoli, avoid varieties with flat/concave heads that trap moisture and promote soft rot. Instead, select varieties with domed heads where water readily drains away.
Avoid damaging vegetables when weeding and during harvest. Minimize any handling of soft-rotted plants, but if you must handle such plants (e.g., to remove them from the garden), wash your hands afterwards with soap and water. Decontaminate garden tools before and after use by treating them for at least 30 seconds with 10% bleach or preferably (because of its less corrosive properties), 70% alcohol. Rubbing alcohol and many spray disinfectants typically contain approximately 70% alcohol. Also, keep insects that can wound vegetables such as cabbage maggot under control (see University of Wisconsin Garden Facts XHT1030,Cabbage Maggot, for details).
Harvest only during dry conditions. Closely inspect vegetables from infected gardens that will go into long-term storage, and be sure not to store any diseased vegetables. Cure vegetables where appropriate prior to storage. Store vegetables in a cool, dry, well-aerated place to suppress bacterial growth.
At the end of the growing season, remove any infested plant debris remaining in your garden, and destroy the material by burning (where allowed by local ordinance) or landfilling it. If soft rot is a serious, recurring problem in an area in your garden, DO NOT grow susceptible crops in that area for a minimum of three years.
For more information on bacterial soft rot:
Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 orpddc@wisc.edu.
Authors: Tobias Lunt*, UW-Madison Plant Pathology
Last Revised: 02/28/2024
D-number: D0010
*Completed as partial fulfillment of the requirements for Plant Pathology 558 at the University of Wisconsin Madison.
References to pesticide products in this publication are for your convenience and are not an endorsem*nt or criticism of one product over similar products. You are responsible for using pesticides according to the manufacturer’s current label directions. Follow directions exactly to protect the environment and people from pesticide exposure. Failure to do so violates the law.
Thanks to Breann Bender, Amy Charkowski, Mary Pelzer, Scott Reuss, Isael Rubio – Salazar and Mary Thurber for reviewing this document.
A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website:https://pddc.wisc.edu.
Send a Plant Sample for Analysis
Be cautious when self-diagnosing plant health issues. Very few diseases can accurately be diagnosed by eye.
Contact theUW Plant Disease Diagnostics Clinic (PDDC), and for a small fee, clinic staff can examine a plant, determine the cause of the disease/disorder, and provide advice on how to control or prevent the issue.
