Sunblotch

Streaked avocado skins may indicate a disease known as sunblotch. And we are not talking about freckles!


​Sunblotch identification

Unlike sunburn damage, which bleaches leaves, sunblotch appears as yellowish, reddish, or white streaks on the stems and skin of avocado fruits. Overall stunting is common and the number of fruits produced may be significantly reduced. Distorted leaves and petioles and rectangular cracking in the bark of older branches may be seen in some cases. Unfortunately, this disease can go unnoticed for years, until symptoms become obvious. By then, several nearby trees have also become infected.


Cause of sunblotch

Until recently, sunblotch was thought to be a genetic disease. We now know that it is caused by a viroid. Viroids are the smallest known infectious pathogens and they only attack plants. Unlike viruses, which contain both DNA and RNA, viroids only contain RNA. This particular viroid attacks many tropical and subtropical plants, but it is seen most often in avocados.


Sunblotch control

Once a tree is infected with sunblotch, it must be removed and destroyed. This means that prevention is your only real course of action. Sunblotch can be transmitted through infected pollen, seeds, and budwood. You can’t do anything about infected pollen if the source is on someone else’s property, but you can invest in disease-free bare root trees. You can also make sure that any grafting projects you take on involve only healthy trees. And be sure to sanitize your garden tools after working on potentially infected trees with bathroom cleaner or a 9:1 ratio of water to bleach.