Bacterial Disease Control

Bacterial Diseases

Bacteria are microscopic single celled organisms. Most bacteria are beneficial, breaking down decaying matter and converting nutrients like Nitrogen to become available to plants. Some bacteria are pathogenic. Depending on the species of bacteria, they release enzymes that degrade cell walls, growth regulators that alter the plants normal growth, toxins that degrade cell membranes and complex sugars that plug water conducting tissue. Bacterial diseases in plants have symptoms very similar to fungal diseases, but a few things set them apart. They often have a rotten or fishy odor, are water soaked with a bacterial ooze, are initially confined between the leaf veins, and may have a chlorotic halo surrounding the infected area. 

Bacterial Leaf Spots

This is the most common symptom of a bacterial disease. Besides spotting on leaves, spots can occur on blossoms, fruits and stems. If the spots increase quickly, it becomes a blight. Bacterial spots will appear as streaks or stripes on monocots.

Almost all bacterial leaf spots and blights are caused by the genera Pseudomonas and Xanthomonas. Brassica production can be particularly susceptible to Xanthomonas. Greenhouse growers can also be haunted by this in ornamental production. The leaf spotting is often contained between leaf veins, or in geraniums appearing as small dots followed by V shaped wedges on the leaf. This highly variable disease will often form halos of yellow around diseased portions of the leaf.  

Bacterial blight, another name for this pathogen, is most experienced during hot weather with high humidity. Overhead watering should be avoided on susceptible greenhouse crops such as zinnia, begonia, English ivy, lavender, hydrangea, poinsettia, geranium, kale, cabbage and peppers. In field production, wounds on plants caused by high winds or farming equipment can allow this bacterium to enter the plant and proliferate. Infected leaves will start showing symptoms including lesions and pale spots. 

A great article on Xanthomonas for greenhouse growers can be found here. Visit the University of Massachusetts Extension site for more information on leaf spot. Biological products such as Cease, Guarda, or Actinovate can be used for bacterial leaf spot management.  


Bacterial cankers appear as sunken dead areas, often in the shape of an ellipse, with thick margins in the bark. Cankers can start with branch dieback, flower collapse, and spotted and yellowed leaves, leaving a shothole in the leaf. Cankers frequently produce a gummy, resinous ooze and discoloration of the affected area. Bacterial canker is a common disease of cherry, plum and peach trees. It is also known as gummosis, blossom blast, dieback, spur blight and twig blight and can lead to the death of the entire tree.

Cankers are primarily caused by Pseudomonas and Xanthomonas in stone fruit and can create decay after harvest. Younger trees are the most susceptible. Prune out infected branches and disinfect pruning tools after each cut to avoid spreading the pathogen. Avoid pruning during cool, wet periods such as fall and spring. Bacterial cankers can be confused with Phytopthora cankers, however Phytophtora cankers are in the lower trunk and roots, while bacterial cankers are in the top portion of the plant.  



Crown gall or root knot are diseases caused by the bacterium Rhizobium radiobacter (Agrobacterium tumefaciens). Entering through a wound in the roots or stem, this pathogen causes enlarged surfaces that are swollen or convoluted and often discolored. Crown gall can infect both woody and herbaceous plants but is more common in fruit trees, Alcea, Argyranthemum, Begonia, Dahlia, Lupinus, Phlox, Crataegus, Euonymus, Populus, Salix, Rosa and Ulmus.

Wilts, Soft Rots and Scabs

Vascular wilts are mainly found in herbaceous crops. The bacteria grow in the xylem vessels, interfering with transfer of nutrients and water. Symptoms are wilting and death. Bacterial soft rot bacteria produce enzymes that break down plant cells. The rotting tissue becomes watery and soft with a foul-smelling ooze.

Soft rot bacteria include Erwinia, Pseudomonas, Bacillus and Clostridium. Bacterial scabs generally infect plants below ground, causing scabby lesions on the outer surface. Potato scab is caused by Streptomyces scabies. This disease commonly affects cotoneaster, pyracantha, hawthorn, quince and raspberry. For disease management, antibacterial sprays are recommended for susceptible plants, like pears in bloom, for prevention.

For control use Actinovate SP, Mycostop, Cease, All-Phase, Long Shadow, Guarda, BioTam, Double Nickel, Regalia and Stargus. Armory may assist with control, although it is not currently labeled as a biofungicide. 

Always review product labels prior to purchase to confirm your purchase is labeled for the specific pest, disease and/or crop you are treating. Accurate identification of pest and/or disease is essential to successful treatment, as are proper cultural and sanitation practices. Local extension offices can help identify pests and diseases. Additionally, feel free to send us images and we will do our best to assist you.

Back to top