Field Guide     Crop Diseases     Bacterial Leaf Spot

Bacterial Leaf Spot

CROPS IMPACTED: Cucurbits, beans, cereals, Coral Bells, Coneflower, pepper, tomato, and other plants.

Bacterial Leaf Spot

Family: Xanthomonadaceae & Pseudomonadaceae

Bacterial Leaf Spot Bacterial Leaf Spot

About Bacterial Leaf Spot

Life Cycle

Bacterial leaf spots are caused by the Xanthomonas and Pseudomonas families of bacteria. These bacteria overwinter in plant debris, but cannot survive for long in soil or water alone. Bacteria infect foliage, fruit, and stems, but require openings such as lesions to get inside the plant because they are relatively weak pathogens. Commonly, insects create lesions from feeding on plants, which the bacteria take advantage of. The pathogen itself is seedborne, which can then spread to other nearby plants after the seedling begins to grow through splashing water and overhead irrigation. Spread of the disease is moderately fast if water splashing is highly prevalent. However, this pathogen is highly dependent on cool and wet conditions, so if these conditions are not met, the pathogen’s distribution will be highly deterred.

Bacterial Leaf Spot Identification and Habitat


The two types of bacteria related to this pathogen produce slightly different symptoms. The Xanthomonas bacteria produce small brown angular and/or circular spots bordered by a yellow tint. On the other hand, the Pseudomonas bacteria cause red-brown angular and/or circular spots that can distort the affected leaf. The spots will appear water-soaked in the early stages and will eventually dry out once lesions are older. A distinct feature of this pathogen is that it causes lesions to turn black quickly after infection. This can be a good way to diagnose the disease early on in its life. In extreme cases, lesions can become numerous and eventually combine together. Bacterial leaf spots oftentimes cause premature defoliation, which can cause sunscalding on fruit. As a result of nutrient deficiencies, sometimes leaves will brown and become wilted. On fruit, the bacteria can create lesions that allow other pests like fungi to invade the fruit.


  • • Xanthomonas
  • • Pseudomonas


The spread of the bacterial leaf spot pathogen is very reliant on specific conditions. Spread is facilitated by wet and cool conditions. Frequent rains are great for the pathogen as this causes plenty of splashing rain for bacteria to be spread from plant to plant. Irrigation using sprinklers also enables rapid spread of bacteria from plant to plant due to water splashing from infected plants, and then landing on non-infected plants. These bacteria’s survival in water and soil without plant remains is limited. Moist conditions generally make it easy for the bacteria to develop. Heavily crowded plants allow disease to be spread easily from plant to plant.

Bacterial Leaf Spot Management and Control Methods

Cultural Control

Before planting, try to ensure that the seeds are disease-free. This is the best method to avoid initial infection and further spread of infection. Using sanitized tools will significantly reduce the chance of bacteria distribution from plant to plant while working with crops. Avoid the use of sprinkler irrigation as sprinklers increase the amount of splashing water amongst crops. This is a major factor in limiting the spread of bacteria between plants. Spacing plants properly is another way to reduce the amount of water splashing from plant to plant. If soil is too wet, improving soil drainage can be very useful to prevent further development and spread of the disease. Removing infected plants is another crucial way of hindering disease expansion. Lastly, crop rotation is should always be considered after dealing with infected crops as it can reduce the chance of crop diseases developing next season.

Chemical Control

When it comes to bacterial leaf spot, there aren’t many chemical methods of control. Due to the lack of bactericides available, chemical controls aren’t the best option. Note that fungicides cannot be used to control bacteria. If managed correctly, cultural controls can be very effective to eliminate or reduce spread of the disease.