Powdery Mildew

Powdery mildew can be a persistent disease of susceptible apple cultivars throughout the United States. It is one of the most predominant diseases in the more arid apple growing areas. It is the only fungal apple disease that is capable of causing infection without wetting from rain or dew.

Powdery mildew causes whitish lesions on curled or longitudinally folded leaves, stunted whitish-gray twig growth evident on dormant shoots, and fruit russeting. Economic damage occurs in the form of aborted blossoms, …

Fire blight

Fire blight is a destructive bacterial disease of apples and pears that kills blossoms, shoots, limbs, and, sometimes, entire trees. The disease is generally common in most apple-growing regions of the US; although, outbreaks are typically very erratic, causing severe losses in some orchards in some years and little or no significant damage in others. This erratic occurrence is attributed to differences in the availability of overwintering inoculum, the specific requirements governing infection, variations in specific local weather conditions, and …

Disease Management in Apple Trees and Fruit

Southern Blight in Apple Trees

Southern blight is a fungus disease caused by Sclerotium rolfsii. The disease is a problem primarily in the Piedmont apple growing region in the southeastern United States. S. rolfsii is a widespread pathogen that affects several hundred plant species. The fungus affects the lower stems and roots of apple trees, killing the bark and girdling the trees. The disease is characterized by the presence of a white, weblike mycelium, which often forms at the bases and on the lower stems …

Apple Scab

Apple Scab

Apple scab is a fungus disease caused by Venturia inaequalis. It is of major economic importance and, if not controlled, can cause extensive losses (70% or greater) where humid, cool weather occurs during the spring months. Losses result directly from fruit or pedicel infections or indirectly from repeated defoliation, which can reduce tree growth and yield.


Apple scab lesions occur on leaves, petioles, blossoms, sepals, fruit, pedicels, and less frequently, on young shoots and bud scales. The first lesions …

What is 'Golden Delicious' necrotic leaf blotch, and how do I identify and manage the disease?

Necrotic leaf blotch (NLB) is a physiological disorder whose occurrence is related to air temperature, light intensity, and soil moisture. The cause of NLB of apple is not known. A hormonal imbalance may be involved because symptoms are enhanced by gibberellins and reduced by abscisic acid. The disorder occurs worldwide on ‘Golden Delicious’ and its bud sports. ‘Golden Delicious’ seedlings vary in susceptibility. ‘Prime Gold’ and ‘Nugget’ are also affected by NLB. For more information, read this article on ‘Golden

What does hail injury look like on apples, and what can I do when it happens?

Hail can injure apple fruit, shoots, and limbs. The extent of the injury usually depends on the size of the hail, its shape, and the duration of the event. Injury can range from torn or shredded leaves and small dents that don’t break the fruit skin to so severe that an entire crop is lost because of physical damage. In some cases, replacement of trees will be necessary, especially when young trees have large amounts of bark injury. Fungicide protection …

What is Powdery Mildew and how do I identify and manage the disease on apple trees?

Powdery mildew on apple is a fungus disease caused by Podosphaera leucotricha. It can be a persistent disease of susceptible apple cultivars wherever apples are grown. It is the only fungal apple disease that is capable of infecting without wetting from rain or dew. Mildew severity and the need for control measures are related to cultivar susceptibility and intended fruit market. For more information and images, read this article on Powdery Mildew on apple trees.

Answer provided by Alan …

What is sooty blotch, and how do I identify and manage the disease on apple trees?

Sooty blotch and flyspeck are surface blemish diseases caused by fungi that commonly appear together on apple or pear in late summer and fall. Although these diseases may shorten the storage life of fruit due to increased water loss, they do not cause decay, and losses are attributed to unacceptable appearance. During wet growing seasons, losses of 25% or more are commonly found even in orchards treated with fungicides. Many fungi are involved in this complex of pathogens, including Peltaster