Disease resistance matters most in apple trees

Chicago Tribune

16-02-2025

If you're considering adding an apple tree to your home landscape this spring, it's important to choose an appropriate variety.
'The particular variety you plant will affect how many apples you harvest, how much work you have to do, and how many pesticides you will need to use for years to come,' said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle.
Apples are susceptible to several serious diseases, including apple scab, cedar-apple rust, fire blight and powdery mildew. These diseases can disfigure the leaves and the fruit, reduce the yield, and weaken or kill the tree over time. The best way to combat them is to choose an apple variety that has been bred to resist them.
The apple varieties whose flavors are familiar from the supermarket, such as Granny Smith, Fuji or Honeycrisp, are sprayed regularly with fungicides and other chemicals in commercial orchards. Those varieties are widely sold for planting because their names and flavors are so well known. But for a home gardener, the wiser course is to seek out more disease-resistant varieties.
'You may have to order them as bare-root plants from catalogs or mail-order nurseries, or ask your garden center to order them for you,' Yiesla said. 'The effort you make now will likely save you far more trouble down the road, when you don't have to spray the tree with fungicides every week.'
For example, the Liberty variety has red skin, white flesh and a sweet-tart taste, and it resists apple scab, cedar-apple rust, fire blight and powdery mildew. Among other disease-resistant varieties are Enterprise, Freedom, MacFree and Williams Pride.
'When you search websites for apple varieties, make a point of checking a variety's resistance to each specific disease,' she said. 'Some varieties are listed as resistant to some diseases but not to others.'
Of course, just because a plant is resistant to a disease does not mean it is immune.
In a plant description, words related to diseases have precise meanings. The word 'immune' means that a plant is not subject to attack by a particular disease or pest. There are no degrees of immunity; a plant is either immune or it isn't. No apple variety is immune to disease.
The word 'resistant' means a plant is generally able to limit the damage from a particular pest or pathogen. The plant may be affected by a disease, but it will likely show less damage than a susceptible variety will.
Even if an apple variety has been bred for increased resistance, that resistance will vary with conditions. In a wet year, a disease-resistant apple tree may still show the symptoms of apple scab and powdery mildew, fungal diseases that are encouraged by high humidity and wet leaves.
Apart from choosing a disease-resistant variety, the only way to reduce the damage from fungal infections is to spray the entire tree with an approved fungicide at regular intervals, beginning in early spring before the buds open. Learn more about apple diseases and their management at mortonarb.org/plant-diseases.
'Investing the time and effort to track down disease-resistant apples or other fruit trees will pay off in the long run,' Yiesla said. 'It will make your home orchard more of a joy and less of a burden.'