Bacterial canker has been observed in late season tomato crops. This article will serve as a review of this important disease.
The symptoms of bacterial canker vary considerably. In most cases, the edges of the leaves may turn yellow and/or brown. That is, the margins of the leaves may become chlorotic and/or necrotic (Figure 1). This symptom, which is sometimes known as ‘firing’, may be more common in a field situation than in a greenhouse. Tomato plants may wilt as a result of bacterial canker. The inside of the stem of affected plants may be discolored brown (Figure 2). The fruit may have bird’s-eye spots-this symptoms is more common in field outbreaks (Figure 3). In the greenhouse adventitious root development may be observed on the stems of affected plants. That is, the stems may develop a ‘bumpy’ appearance where extra roots are starting to develop. However, this symptom may also develop from stresses other than bacterial canker .
Figure 1. Bacterial canker may cause leaf margins to become necrotic and chlorotic.
Figure 2. Bacterial canker may cause the stem of tomato plants to be discolored.
Figure 3. Bacterial canker of tomato sometimes will result in fruit symptoms such as shown here.
The bacterium which causes bacterial canker of tomato may survive in seed, crop debris, volunteer tomatoes and equipment such as wooden stakes. The pathogen may spread from plant to plant by splashing. This is most likely during transplant production in the greenhouse. Once infected, tomato plants may continue to develop symptoms, which may give the appearance of spread in the field. Bacterial canker may be observed in the field or high tunnel/greenhouse situation.
The most important factor in managing bacterial canker of tomato is to avoid seed contaminated with the pathogen or transplants that have symptoms. Heat treatment of seed to reduce contamination is possible; see the Midwest Vegetable Production Guide for Commercial Growers 2021. Use only new or sterilized planting stakes, transplant trays and other planting equipment. The use of copper and mancozeb products for management of bacterial canker of tomato is more effective in greenhouse transplant production than in the field.
It is important to manage greenhouse transplants carefully.
- Treat seedlings in the greenhouse starting at about the first true leaf stage and at 5 to 7-day intervals. Use a combination of copper and mancozeb. Streptomycin products such as Firewall® or Harbour® may be used starting at the 2-leaf stage. Do not apply streptomycin products in the field.
- Peroxide products such as Oxidate® may be used in addition to the ones mentioned above. Be careful with mixing the Oxidate® with other products. For example, if you mix copper and Oxidate®, mix Oxidate® at 0.33%. If you apply Oxidate® alone, use 1.0%. Oxidate® has no residue. Therefore, it is best to apply this product frequently. Do not substitute Oxidate® for copper or any other product.
- I have thoughts on how to apply products by hand. I favor a backpack sprayer rather than a garden sprayer. See this video about the use of backpack vs garden sprayers.
- If you grow different varieties, separate them in the greenhouse so that there is no splash between varieties. If you have different lot numbers of the same variety, also separate these.
- Scout the plants for symptoms.
The severity of bacterial canker depends in part on when the plant is affected. If transplants are infected, the disease is likely to be quite severe. If the disease affected plants after first fruit, then the disease may not be severe until late in the season. It is important to either avoid bacterial canker in your operations or delay the disease as much as possible.