Basic Information | Advanced Information | Diagnostic Information
Bacterial canker can occur in tomatoes as a primary systemic infection or a secondary foliar infection. The disease shows a wide range of symptoms and can affect plants at all growth stages. Primary systemic infections originate from infested seed or by being introduced into the vascular tissue of seedlings, transplants or plants. Initially stunting and wilting will be observed followed by open cankers on the stem. When the stems are split open lengthwise a thin, reddish-brown discoloration is observed inside of the vascular tissue, especially at the base and nodes of the stem.
Secondary late infections are spread through splashing rain or irrigation water, wind-driven rain, and contaminated equipment, tools or workers. Secondary infection symptoms include browning of the outer edges of the leaflets with a thin yellow band, referred to as “firing”, upward leaflet curling and fruit lesions. Lesions on the fruit are small (1/32 to 1/16 inch) tan colored spots surrounded by a white halo that resemble bird’s eyes and are often referred to as “bird’s-eye” spots.
Sources of the pathogen for this disease include seed, crop debris, infected weed hosts and volunteer plants and contaminated equipment or tools. Infected seed is the major source of primary systemic infections however the pathogen can enter into the plant vascular tissue via natural openings and wounds also resulting in systemic infections. The pathogen can survive on the seed coat as well as within the seed making it difficult to eradicate from the seed. The pathogen can enter into the plant via natural openings and wounds. Secondary late infections in the field are spread through splashing water, wind-driven rain, and contaminated equipment, tools or workers. In the greenhouse, high plant density and humidity and warm temperatures provide optimal growth conditions for the pathogen. Overhead irrigation and water splashing contribute to the spread of secondary infections in the greenhouse. Plant management practices such as pruning, suckering and harvesting can result in the more serious primary systemic infections in poor sanitation practices are utilized.
Favorable Environmental Conditions
Optimal conditions for bacterial canker are high moisture, high relative humidity (≥ 80%) and warm temperatures (75-90 °F).
Often Confused With
- Bacterial Leaf Spot – Look for large crusty lesions on the fruit with no white halo as indicators of bacterial spot.
- Bacterial Speck – Look for small black pin-point lesions on the fruit with no white halo as indicators of bacterial speck.
- Early Blight – Look for lesions with concentric rings and chlorosis as indicators of early blight.
- Mite Damage – Using a hand lens look for live mites on the leaf surface as indicators of mite damage.
The pathogen can be active from the time of plant emergence through to harvest. Seedlings in the greenhouse should be carefully monitored for early symptoms and suspect plants should be removed from the greenhouse and submitted for plant disease diagnosis. Plants in the field or greenhouse should be monitored twice a week for disease symptoms. Plants with disease symptoms and adjacent healthy- appearing plants should be removed and discarded.
No thresholds have been established for this disease.
Bacterial canker is very difficult to manage once it has been introduced into the crop therefore preventative measures are the most cost effective way to manage bacterial canker.
- Start with clean seed – Purchase certified, disease-free seed or sanitize seed with hot water, sodium hypochlorite (bleach) or hydrochloric acid. Here is a link to The Ohio State University Extension Fact Sheet for Hot Water and Chlorine Treatment of Vegetable Seeds to Eradicate Bacterial Plant Pathogens.
- Start with clean transplants – Scout plants daily and destroy plants once a plant disease diagnostic laboratory or an on-site diagnostic assay has confirmed the disease. Apply one or two preventative copper fungicide applications and one application of streptomycin to the plants before transplanting them into the field.
- Start with clean equipment and tools – Clean and disinfect all tools and farm equipment prior to working with the transplants or plants. Good sanitation practices are critical to prevent contamination and cross contamination of plants by the bacterial canker pathogen.
- Start with a clean field – The bacterial canker pathogen can survive in the field as long as there is infected crop debris present. Rotate with a non-host before re-planting the field with tomato. Ideally a 3-4 year out of crops in the same family as tomato (pepper, eggplant and tobacco) should be implemented. Plant into a field free of weeds or volunteer tomato plants.
- Use best cultural practices – Use management strategies that maintain reduced-stress growing conditions. Provide plants with adequate but not excessive nitrogen, improve the organic matter content of the soil through the use of composted green or animal waste or cover crops, use well-drained soil and avoid overhead irrigation if possible.
- Use crop protectants – Field applications of copper fungicides may slow secondary bacterial canker development over the growing season.