Several types of fungi specifically attack citrus fruit, including lemons, grapefruit and limes. These fungi can be detrimental to the yield of a citrus tree as well as harmful to the taste of the fruit. In order to prevent fungus from destroying a fruit plant, it is necessary to know the different types of fungus that feed upon it.
Melanose, a type of fungus, affects the surface of citrus fruits without damaging the meat of the fruit. Although melanose generally appears as a collection of dark brown to black spots, in some places, the mold appears as a whitish color. You can remove melanose with the fingernail; melanose does not extend into the fruit itself. Protecting copper sprays treat and control melanose; the time to spray the copper spray is specific and depends on the type of fruit on which the melanose grows.
According to the University of Guelph, penecillium causes a white mold to grow on the surface of a fruit. Eventually, this white mold turns either green (Penicillium digitatum) or blue (Penicillium italicum). Cool temperatures, moisture and the fruit's natural sugars all influence the growth of penicillium. The British Columbia government website suggests warm environments (to remove dew) and the burning or burying of all affected fruit to remove penicillium.
According to the Texas Agricultural Extension Service, phytophthora, also called brown rot, attacks fruit in high moisture environments (such as during heavy rains). The progression of the fungus begins with a white, soft spot that smells strongly of fermentation. Eventually, the white fungus will turn dark brown and possess the feel of leather. Because of the moisture needed for growth, lower fruits on the tree attract phyphthora more readily. Winds can carry the mold to higher fruit after time. Proper sanitation, refrigeration and disinfection during transport remove phyphthora most effectively, according to the Texas Agricultural Extension Service.