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Bacterial diseases of vegetables

M. Grabowski, UMN Extension Educator

The bacteria that cause black rot in cabbage spread through the
plant's veins in the field and in storage.
M. Grabowski, UMN Extension
The high heat and humidity this summer, combined with multiple heavy rain events have created ideal conditions for many bacterial plant pathogens to multiply and spread. This is especially evident in the vegetable garden, where black rot can be easily found on cabbage, kale, and broccoli, beans bear spots and browning from bacterial leaf blights, and tomato and peppers are spotted by bacterial spot.

Bacterial plant pathogens have several unique features that make them good plant pathogens. Many are able to infect seed and can be introduced into the garden unseen on infected seed or transplants.

Bacterial diseases of bean often result in spots on leaves and
 bean pods. M. Grabowski, UMN Extension
Bacteria are covered in a sticky coating and are easily spread through the garden on hands, tools, and insects. Many bacterial plant pathogens are also easily spread by splashing rain or sprinkler irrigation. Bacteria infect the plant through natural openings or wounds. They multiply within infected plant tissue and can survive from one growing season to the next in infected plant debris in the soil.

Many management strategies for bacterial plant diseases are designed to prevent the introduction and spread of the pathogen. For example, gardeners should buy healthy seeds and transplants from a reputable source and use drip irrigation instead of sprinklers to keep leaves dry.

At this time of year, there are still a few things that gardeners can do to manage bacterial diseases. 
  • Avoid working in plants when they are wet. 
  • When working in the garden, take care of healthy plants before working in infected plants. 
  • Clean tools with solution of 1 part household bleach and 9 parts of water after working in infected plants. Clean hands with soap and water. 
  • Up to 1/3rd of infected leaves can be removed from an infected plant to reduce disease spread. (At this time of year, this is practical for crops like Brussels sprouts and kale that are still developing a crop, but is not necessary for tomatoes, peppers, and beans, which are near the end of their natural production cycle.)
  • Remove infected plants that are no longer producing a crop. 
  • Do not save seed from infected plants. 
Seed saved from tomato fruit infected by a bacterial plant
pathogen may be infected with the bacteria.
M. Grabowski, UMN Extension 

Diseased plant material can be composted if the compost pile heats up to 148 F and all plant material becomes broken down. Many counties offer municipal compost sites that accept yard waste. If composting is not an option, infected plants should be buried in the soil soon after harvest. The soil microorganisms will begin to break down the infected plant material. The pathogen would be expected to survive in the soil and plant debris for 1 to 2 years. As a result, the same crop and related plants should not be planted at that site for the next 1 to 2 years.

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