Apple Measles

Who knew apples could get the measles?

Unlike the human variety, which is caused by a virus, apple measles is a symptom of manganese toxicity.

Apple exhibiting measles from manganese toxicity University of Georgia Plant Pathology , University of Georgia, Bugwood.org CC BY-SA 3.0

Manganese

Manganese is a micronutrient used by plants to make chlorophyll. It is an important component of chloroplasts. Manganese is used by all living things as an antioxidant, to counteract the toxic effects of oxygen. Manganese can also be phytotoxic, which means it can be poisonous to plants. ​

Symptoms of apple measles

The first sign of apple measles is tiny red pustules on new twigs. If you look closely, you can see that the tissue in the center of each pustule is dead. Take a look on the inside of the twig and you will see that the lesion spreads, under the bark, into the cortex or the phloem tissue.  If you take a cross-section of the twig, you will see brown streaks or flecks. As the affected twig matures, the bark thickens, cracks, and sloughs off, leaving flakey cankers. This flaking off of bark can last for several years.
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Bark measles on an apple tree (William M. Brown Jr., Bugwood.org) CC BY-SA 3.0

​Treating apple measles

Since apple measles is a symptom of too much manganese in the soil, you need to alter the soil chemistry to help your apple tree. Apple measles occurs most commonly in acidic soil, so increasing the soil pH with lime or other alkaline soil amendment will help reduce future damage.

Unfortunately, it is very difficult for trees to recover from apple measles, so get your soil tested every 3 to 5 years, so you know what they are dealing with - before the damage is done.