Botryosphaeria obtusa

Symptoms

Black rot

Botryosphaeria 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 color. 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.

Canker

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

Botryosphaeria obtusa is the pathogen of black dead arm disease of grapevine. It has been shown to be able to oxidise wood δ-resveratrol into delta-viniferin.