Sunblotch

Streaked avocado skins may indicate a disease known as sunblotch.
 
Sunblotch identification

Unlike sunburn damage, which bleaches leaves, sunblotch appears as yellowish, reddish, or white streaks on the stems and skin of avocado fruits. Common symptoms of sunblotch include stunting, distorted leaves and petioles, and reduced fruit production. Rectangular cracking in the bark of older branches may also occur. Unfortunately, this disease can go unnoticed for years before symptoms become visible. By then, several nearby trees have probably become infected.

Cause of sunblotch

Until recently, botanists thought sunblotch was a genetic disease. Now we know it is a viroid infection. Viroids are the smallest known infectious pathogens, and they only attack plants. Unlike viruses, which contain DNA and RNA, viroids only contain RNA. This particular viroid attacks many tropical and subtropical plants, including avocados.

Sunblotch control

Trees infected with sunblotch must be removed and destroyed. Tree removal is expensive and potentially dangerous, so prevention is the only option.

Sunblotch spreads through infected pollen, seeds and budwood. You can’t do anything about infected pollen if the source is on someone else’s property (besides educating your neighbor). But you can invest in disease-free bare-root trees. You can also ensure 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 a household cleaner.