Friday, December 23, 2011

Grapefruit Melanose

What causes the brown speckling on the skin of grapefruit?  The staining is a fungal disease known as melanose. This disease displays a very interesting pattern on the fruit called ‘tear staining.’ It is caused when dew, contaminated with spores, runs down over the surface of the fruit. As this happens, the fungal spores can stick to the skin of the fruit. These spores germinate and cause tiny spots on the fruit in the pattern of the water running down the fruit, hence the name ‘tear staining’. 

Unless the disease becomes very severe, melanose is considered a cosmetic problem and, in commercial operations, will cause a downgrading of the fresh fruit. 
For the homeowner, the fruit is just as good inside as any perfect looking piece of fruit at the supermarket.

With an abundance of rain, the spores splash to nearby leaves and twigs, causing leaf drop and twig dieback.  Many of the dead twigs we see in citrus trees are caused by this fungus.  (Note: In high numbers, scale insects can also cause twig dieback.)

Although a tedious job, it is best to prune out all the dead twigs, they are store houses of the fungal spores.  However, whether you prune or not, the trees will not die from melanose.