The infection that occurs the most frequently is green mold and it is caused by the mold Penicillium digitatum. It exists in all citrus fruit growing regions and is a serious threat to the citrus industry.

When the fruit is bruised or punctured while it is being harvested or packed, the mold enters the fruit through these wounds and therefore, this disease can be contracted by fruit on the tree, in the packinghouse where the fruit is prepared for the market, while in transit to the store, in storage, and the retail store.

At first, only a white mold is seen growing on the outside of the fruit and later begins to turn green due to the large amount of spores that are being produced on the surface of the fruit. The fruit begins to decay and become soft. It shrivels up and dies as a result.

Blue mold is caused by the fungus Penicillium italicum and it is different from green mold mainly because of the color. The conditions that the two molds grow in are very similar and tend to grow best at around 75 degrees Fahrenheit.

Their growth is slowed by lowering the temperature and cooling fruits while they are being stored and shipped are a good way to decrease the amount of infections in a shipment. Losses from these molds can also be greatly reduced by taking special care during harvesting and transporting not to bruise or break the skin of the fruits.

Fruits mainly become infected when their outer skin is broken and mold spores make their way inside either from contaminated soil, another infected fruit, or through the air. Fungicides can also be used to reduce the amount of infections. Also, any equipment used to pack the fruit and anywhere they are stored should be sanitized every day to reduce the chance of the fruit becoming infected.

The spores of both of these molds are very easily spread by air currents and any fruits that are contaminated with them should not be exposed to wind or other currents of air near any healthy fruit due to the likelihood of it becoming infected.

Fruits can also become infected due to other physical injuries such as those associated with stem-end rind breakdown and chilling injuries.