Apple scab on leaves

The two primary diseases affecting apples in the upper Midwest are apple scab and fire blight.

The easiest way to prevent these diseases is to plant resistant varieties.

If you plant susceptible varieties, there are ways to prevent and manage infection.

Keep the area around apple trees tidy and free of debris, fallen fruit and leaves, pruned branches, and weeds throughout the year.

Apple scab on fruit

The first signs of this disease can often be found on the under surface of the leaves as they emerge from the buds in the spring.

Apple scab spores are blown around in the air and land on the under surface of leaves.

As the leaves continue to grow, both surfaces can be infected as can the fruit.

The signs to look for on leaves are velvety, brownish, small circles.

As the infection takes hold, these lesions start to grow together and the surfaces of leaves and fruit become distorted.

Keeping scab infection to a minimum begins with raking and removing leaves from under the tree the previous fall. Planting varieties that are resistant to scab is another way to minimize infection. William's Pride, Freedom, and Liberty are immune to this disease. Honeycrisp has some immunity as well.

If the variety you plant is not immune and you see signs of scab early in the season, the best way to protect the fruit is by covering it with a plastic bag or applying a well-timed spray of organic fungicides such as lime sulfur.

The telltale symptom of fireblight is brown, 'shepherd's crook' shoots.

Fire blight is caused by a bacterial infection that can kill blossoms, shoots, and eventually entire trees. You might see this disease on the trunk or limbs of a tree as a sunken area with discolored bark. As the lesion gets bigger, it begins to crack around the edges and the tree will look like it has been burned, thus the name fire blight.

You also might see the disease developing on new shoots as they grow in the late spring. When shoots are infected, they turn from green to brown to black, also appearing as if burned. The shoot will develop a crook at the end of the shoot.

The best approach to managing fire blight is prevention.

Plant fire blight resistant varieties.

Plant trees in a spot that is well-drained, has full sun and plenty of air circulation.

Keep the area around the tree very clean and free of debris, fallen fruit and foliage, pruning debris and weeds.

Fire blight is most prevalent in young, fast-growing trees. If you see symptoms of the disease, timing is critical because the disease moves quickly through the tree.

Prune out infected shoots at least 6 inches behind the browning area of that shoot.

After each pruning cut, disinfect pruners in a dilute bleach solution so you don't spread the infection with your pruners.

If branches have fire blight lesions, prune those out well behind the infected area. This may affect the look of your tree, but it will potentially save the life of your tree.

Avoid hard pruning while the tree is young (up to 3 years) and limit nitrogen fertilizers, both of which cause excessive growth.

Hail damage

Hail damaged fruit

Hail is common in the upper Midwest, occurring at times during the height of summer. Depending on the size of the hail, time of year, and duration of the hail event, damage can occur on flowers, fruit, foliage, shoots and branches.