Bacterial spot of tomato and pepper, bacterial scab, black spot
Xanthomonas vesicatoria. Previously, Xanthomonas campestris pv. vesicatoria. Several strains are recognised, infecting tomato, pepper or both.
Worldwide. In temperate and tropical countries. Asia, Africa, North, South and Central America, Europe, Oceania. It has been recorded from American Samoa (tomato), Australia (capsicum, tomato), Cook Islands (capsicum), Federated States of Micronesia (tomato, capsicum), Fiji (capsicum, potato, tomato, Solanum weed), New Caledonia, New Zealand, Palau (capsicum, tomato), Solomon Islands (tomato), and Tonga (capsicum).
Tomato, capsicum, chilli, and weeds in the Solanaceae family, for instance, Datura, Physalis (cape gooseberry) and Nicotiana (tobacco) species.
The spots are small, numerous (Photo 1), sunken on the upper leaf surface, and slightly raised below. Single spots are up to 3 mm; merging, especially at the leaf tips and margins, and leaves look scorched and turn yellow; sometimes the lower leaves die and fall. Spots on the leaf stalks and stems are elliptical (Photo 2). Spots occur on the young fruits as raised scabs (Photo 3).
The bacteria infect leaves through natural openings; fruit are infected through wounds, which occur when fruits rub together or when bitten by insects.
There are several ways that the bacteria spread:
Bacterial spot survives between crops in crop remains, soil, on seed, and on wild hosts.
Bacterial spot is a serious disease. It is especially severe in warm, wet and windy conditions, causing plants to lose their leaves. Damage to fruit occurs (i) when the disease comes early as mostly young fruit are infected; and (ii) when leaves drop exposing the fruit to the sun.
Look for many small (2-3 mm) irregular spots on the leaves, leaf stalks, stems and fruits. Spots on the leaf stalks and stems are elongate, i.e., longer than they are wide. Look for scabby spots on the fruits with transparent margins.
Control of bacterial spot relies on: (i) growing healthy plants from seed free from infection, and (ii) care in handling seedlings when transplanting them from nursery to field.
Cultural control is important, as it is difficult to control this disease with chemicals. Not only are the chemicals expensive, but also they are easily washed off leaves and fruits in heavy rain showers that occur frequently in Pacific island countries.
There are resistant varieties of capsicum.
Use copper fungicides, or copper plus mancozeb. It is very important to have healthy seedlings free from bacterial spot, so spraying should start in the nursery, and continue at 7-10 day intervals in the field. Spraying early, when the plants are young, is especially important as in wet, windy weather, sprays alone often fail to give adequate control.
AUTHORS Helen Tsatsia & Grahame Jackson
Information CABI (2014) Xanthomonas vesicatoria Crop Protection Compendium (http://www.cabi.org/cpc/). Photo 3 Diseases of vegetable crops in Australia (2010). Editors, Denis Persley, Tony Cooke, Susan House. CSIRO Publishing. 1An alternative treatment is to soak seed in 1.3% solution of sodium hypochlorite for 1 min, then rinse and dry.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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