The fruit in this picture is infected with a fungal disease called brown rot of citrus. Not only will the fungus infect fruit, but the trunk and roots as well. The fungal spores will splash up on low hanging fruit during a heavy rain storm. The spores germinate, grow and cause the fruit to rot and eventually drop. As the rain continues, so does the disease, spreading to fruit higher and higher in the tree. Infected fruit will turn light brown and become soft and leathery. Eventually the whole fruit will rot.
A copper fungicide is often used
as a preventive spray - it will not, however save the already infected fruit. Repeat
applications of copper will be needed if the rain continues. Another method of
control is to mulch the ground underneath the tree. This will help in preventing fungal spores on the ground from splashing up into the tree and infecting the
fruit. In dry years, the disease will be
mild, but it will thrive in years of high rainfall.
