|Symptoms of black rot|
(Schwein.) Shoemaker (1964)
Botryosphaeria obtusa is a plant pathogen that causes Frogeye leaf spot, black rot and cankers on many plant species. On the leaf it is referred to as Frogeye leaf spot; this phase typically affects tree and shrubs. In fruit such as the apple, cranberry and quince, it is referred to as black rot, and in twigs and trunks it causes cankers.
B. obtusa enters the fruit through wounds. These can be made by insects, birds or growth cracks. At first a brown spot, near the calyx, appears on the fruit. The spot on the fruit then enlarges and black/brown rings appear on the fruit. The fruit holds its shape, however, unlike other fruit diseases. The fruit will then wither up and can remain on the tree for another year before falling off. During this time pycnidia appear on the surface of the rotted fruit.
Frogeye leaf spot
In leaves the fungus begins by causing purple specks on infected leaves. These then enlarge to cause large spots on the leaf, developing a brown colour. The spots appear to have rings of brown with a purple margin, thus giving it its frogeye appearance. The spots can then produce pycnidia which can separate this species of fungus from other possible leaf fungi.
On twigs, branches and trunks B. obtusa can infect where there has been a winter injury or fire blight cankers. Slightly sunken reddish/brown spots appear on the infected areas of bark. These then enlarge to form cankers, which can then enlarge slightly more each year. The bark usually dies and can, after time, be pulled away from the tree. In older cankers the pycnidia appear on the bark.
Black dead arm disease of grapevine
Treatment and control
The most effective treatment is to prune out the infected areas on trees, to ensure transfer between trees does not occur. Fruit that is infected can stay on the tree for over a year, and therefore remaining fruit should be removed to avoid another source of inoculation for other trees. The trimmed branches or dead fruit should then be burned or disposed of immediately as the organism can survive on the dead tissue for a long period of time. Infection of leaves and fruit can be avoided by spraying them with a fungicide. The treatment for the fungicide should be also kept up to date via the manufacturer's instructions.
- Hartman, John (2004). "Frogeye Leaf Spot, Black Rot and Canker of Apple" (PDF). University of Kentucky. Retrieved 2007-10-30.
- Ellis, MA. "Black Rot and Frogeye Leaf Spot of Apple". Ohio State University. Archived from the original on 2007-10-24. Retrieved 2007-10-30.
- Travis, JW; Rytter, JL; Briggs, AR. "Black Rot, Botryosphaeria obtusa". West Virginia University. Retrieved 2007-10-30.
- Identification of phytotoxins from Botryosphaeria obtusa, a pathogen of black dead arm disease of grapevine. Jules Désiré Djoukeng, Suzanna Polli, Philippe Larignon and Eliane Abou-Mansour, European Journal of Plant Pathology, Volume 124, Number 2, pages 303-308, doi:10.1007/s10658-008-9419-6