Lenticel damage among problems in Honeycrisp and other varieties

Lenticel damage has become increasing problematic over the past decade. This season, Michigan State University Extension observed a considerable amount of fruit across the state with symptoms. There are many factors that contribute to lenticel damage and other spots. Research is ongoing to identify and describe them, as well as to provide recommendations for management.

Honeycrisp has been the worst offender for apple spots this season, as it has been historically. This variety is susceptible to several fruit spots, including lenticel damage, bitter pit and spray injury. Brown marmorated stink bug can also cause damage that mimics lenticel damage in all apple varieties.

Lenticel damage has been observed in many locations across the region, while bitter pit has only been observed in very few locations. These two kinds of spots can be difficult to distinguish. Lenticel damage typically has defined edges and is associated with a lenticel, while bitter pit has sunken, irregular, mostly diffuse edges (see photos at top of article).

Causes of fruit spots are numerous and variable. In addition, some varieties, planting systems and locations appear to be more susceptible than others. Lenticel disorders are most likely related to physiological stress from earlier in the season, frequently associated with moisture (too much or lack thereof). The result is cell cracking as the cells expand or contract too quickly, which develops into lesions later in the season. Lenticel damage may also be caused by sunburn or heat stress, as well as chemical injury. Therefore, it is important to look at individual blocks’ spray history, environmental conditions, to diagnose the cause and prevent it in future seasons.

There are a number of resources available to help identify various spots and causes. This chart of lenticel related disorders developed by Washington State University and U.S. Department of Agriculture scientists is useful for describing various symptoms.

In addition, this presentation describing fruit rots and lenticel injury from Cornell University given by David Rosenberger and Srdjan Acimovic helps tease apart the various types of injury on Honeycrisp and other varieties. Lenticel damage can also lead to lenticel infections, as summarized in this article on lenticel infections and bitter rot by Bill Shane of Michigan State University Extension. There are many contributing factors and unknown causes of lenticel injury.

– Anna Wallis and Amy Irish-Brown, Michigan State University Extension 

Lenticel damage (left) and bitter pit (right) symptoms in Honeycrisp fruit. Photo:  Anna Wallis/MSU Extension