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Fruit Notes

Evaluation of Scab on Fruit of New Apple Cultivars

Fruit Notes

Daniel R. Cooley, Arthur Tuttle, and James Hall
Department of Microbiology, University of Massachusetts

Duane Greene
Department of Plant and Soil Sciences

Fruit Notes

While scab resistance has not proven to be the most important characteristic of new apple cultivars, it is still useful to know how susceptible new cultivars are to scab. A grower is probably wisest to choose a new cultivar based on marketability and production, but then treat it for scab according to susceptibility to the disease.

It was difficult to control scab in 1998, and a test block of new cultivars at the Horticultural Research Center in Belchertown, MA developed significant foliar and fruit scab over the growing season even though fungicides were applied. These cultivars were planted in five replicated blocks, and we decided to evaluate scab incidence to determine if there were differences. All the trees were on M.9 rootstock, except two that also were on Mark (Golden Delicious and Yataka). On September 3, 1998, scab on the fruit was evaluated, and incidence was calculated as a percent of total fruit per tree.

The only cultivar in the planting that is already widely planted commercially in Massachusetts is Golden Delicious. Golden Delicious is generally reported as not very susceptible to scab, and this evaluation supported that assumption. While Golden Delicious had about 10% scab incidence, scab incidence over the whole planting ranged from 0 to 49%. Gala Supreme was quite resistant to scab, with 0% incidence. Similarly, Sansa, a Gala x Akane cross, also had 0% scab. As might be expected, two scab-resistant cultivars from the Purdue/Rutgers/Illinois program, Enterprise and Goldrush, and one from the New York program, NY-75414-1, also did not show any scab. Suncrisp, progeny of a Golden Delicious cross, had very little scab (6%).

Unfortunately, two cultivars that would have been very interesting to evaluate, Honeycrisp and Ginger Gold, did not produce fruit in 1998. Braeburn and Fuji were both quite susceptible to apple scab.

Results of this test were similar to those in formal disease analyses done in Connecticut, Michigan, New York, Virginia, and West Virginia

All apple cultivars do not get scab to the same degree. The key question, for which we do not yet have an answer, is how much less can we spray the less susceptible cultivars? That will have to be researched.