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Agronomy Day 2007

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Important Bacterial Diseases of Tomatoes in Illinois

figure 1
Fig. 1. Foliar symptoms of the bacterial diseases of tomato.
Mohammad Babadoost
Associate Professor
Department of Crop Sciences
(217) 333-1523; babadoos@illinois.edu

Bacterial diseases of tomatoes occur in commercial fields and home gardens in Illinois every year, causing up to 100% crop losses. Major bacterial diseases of tomatoes in Illinois are: bacterial canker, caused by Corynebacterium michiganense pv. michiganense; bacterial spot, caused by Xanthomonas campesiris pv. vesicatoria, and bacterial speck, caused by Pseudomonas syringae pv. tomato. These bacterial diseases can be distinguished from each other on the basis of fruit symptoms. Management of all three bacterial diseases is similar and requires cultural practices and preventive chemical applications, mainly copper compounds. Bacterial canker is more destructive than other two diseases.

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Fig. 2. Tomato fruits with bacterial canker symptoms.

Bacterial Canker
The early symptoms of the disease on the foliage are wilting, curling of leaflets, and browning of leaves. As the leaves die, the petioles remain green and firmly attached to the stem (Fig. 1). A cut through the stem shows yellowish brown discoloration of the vascular element. Fruit symptoms may be observed at any age, but are usually seen first on green fruit 1/2-2 inches in diameter. White spots 1/8 inch in diameter develop on the fruit (Fig. 2). The spots have a dark brown center, which becomes raised, and are surrounded by a distinct white halo; they have been termed “bird’s-eye spots.”

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Fig. 3. Tomato fruits with bacterial spot symptoms.

Bacterial Spot
Infected leaves show small, irregular, dark lesions (Fig. 1), which can coalesce and cause the leaves to develop a general yellowing. Symptoms on fruit appear as black spots. The spots on green fruit are as small water-soaked, slightly raised lesions, measuring 1/8 to 1/4 inch in diameter (Fig. 3). Gradually, the spots become brown, slightly sunken, with rough and scabby surface.

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Fig. 3. Tomato fruits with bacterial spot symptoms.

Bacterial Speck
Infected leaves develop small, black lesions, often with a discrete yellow halo (Fig 1). Infected fruit develop lesions, which are small, sunken, black spots surrounded by darker green haloes (Fig. 4). On ripe fruit, spots are dark brown to black, superficial flecks. The symptoms of bacterial spot and bacterial speck on foliage are similar. These two diseases are more readily distinguished on the basis of fruit symptoms (Figs. 3 & 4).

For management of bacterial diseases of tomatoes, the following recommendations should be practiced: (1) use only certified, pathogen-free seed; (2) plant only certified, disease-free transplants; (3) in greenhouse, seedbeds and soil must be sterilized; (4) practice 2- to 3-year crop rotation with non-host crops; (5) follow good sanitation programs; (6) in the field, control irrigation to minimize plant wetness; (7) control the weeds; and (8) spray of copper compounds could help in protecting healthy plants. For more information on chemical control of tomato bacterial diseases in commercial fields, consult the Midwest Vegetable Production Guide for Commercial Growers (www.entm.purdue.edu/entomology/ext/targets/ID/index.htm)