Tobacco frog-eye leaf spot
Worldwide. In the tropics. Asia, Africa, North (Hawaii) and South America, the Caribbean, Europe (restricted), Oceania. It is recorded on tobacco from Australia, Federated States of Micronesia, Fiji1, New Caledonia, Palau, Papua New Guinea, Solomon Islands, Tonga, and Vanuatu.
Tobacco, and other members of the potato (Solanum) family, tomato, eggplant, and weeds.
A common fungal disease wherever tobacco is grown, developing in the nursery (plant bed), field or barn after harvest. Spots, circular 2-15 mm diameter, brown, grey or tan, with dark borders (Photo 1). The centre of the spots becomes papery. Tiny black structures can sometimes be seen in the centres of the spots; these are groups of stalks and their spores (Photo 2).
The spots are mainly on the lower mature leaves at first, moving up the plant as the season advances. The spots continue to develop after harvest on the cured leaves.
Spread is from airborne or soilborne spores. There is a possibility that the spores are seedborne, too. Survival between crops occurs in trash from the harvested crop, on other related crops and weeds. The disease is worse in hot, humid weather.
A disease of minor importance. Its impact is greatest in Central America, West Africa and South Asia. In Central America, it is more important in shade-grown cigar varieties. The fungal infections lower the quality of the tobacco smoke, reducing some ingredients (alkaloid, sugar and phenol) and increasing others (e.g., nitrogen).
Look for the circular brown spots, 2-15 mm diameter, with white or pale brown centres, and dark margins.
There are resistant varieties, with resistance transferred from related species.
If fungicides are required, use mancozeb, copper or chlorothanonil.
AUTHORS Grahame Jackson & Eric McKenzie
1Information from Graham KM (1971) Plant diseases of Fiji, HMSO, London. Photo 1 R.J. Reynolds Tobacco Company Slide Set, R.J. Reynolds Tobacco Company, Bugwood.org. Photo 2 Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org.
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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