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Honeycrisp Leaf Complex

This article was reviewed by the editor of Orchard Network for technical accuracy and appropriateness.

Honeycrisp (Figure 1) is a large, bicolored apple introduced by the University of Minnesota's apple breeding program in 1991.

Figure 1. Honeycrisp apples grown at the Horticultural Experiment Station, Simcoe.

It has an aromatic, sub-acid flavor with a good acid-sugar balance. One of its primary outstanding attributes is its crispness and keeping quality - unusual traits for an apple that matures in early to mid September.

Another uniqueness of this cultivar is that it commonly develops a leaf complex indicated by interveinal chlorosis and leaf blotchiness - not very dissimilar to a nutrient disorder. It is not known what causes these symptoms, or whether it is of any physiological consequence to the tree or fruit. However, indications thus far seem to indicate that it is genetically based because it is so widespread wherever Honeycrisp is grown.

The leaf complex symptoms appear on extension shoot leaves early, worsen throughout the growing season and persist until leaf drop when leaves often become much browner in comparison with other cultivars (Figure 2). Its presence is more prevalent on trees with lighter crop loads and trees with less vigour (Figure 3). Although the symptoms resemble potato leafhopper damage, research in New York has ruled this out as a primary cause. Also, our lab has tested healthy and affected leaf tissue for macro or micro nutrient levels, and none appeared deficient. We have further screened trees from several Ontario and Nova Scotia orchards for viruses, and although some latent viruses were identified to be present, it is not clear whether they are explicitly contributing to the leaf complex. Dr.'s. Lailiang Cheng and Jim Schupp are postulating that the symptoms may be a result of excessive starch accumulation in the chloroplasts of leaves. This may be the result of impaired movement from the leaf to other parts of the plant such as fruit or roots. Regardless of the cause, orchardists growing Honeycrisp will soon discover these symptoms - and might initially be quite concerned. They can be assured that is common and at this point, does not appear to substantially affect tree health or productivity.

Figure 2. Close-up of leaves affected by leaf complex

Figure 3. Symptoms are more prevalent on younger terminal leaves and on trees with light crop loads