Category: Apples

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Thread Blight of Apple

Thread blight is a fungus disease caused by Corticium stevensii. Primarily, the disease is a problem in poorly managed orchards in the southeastern United States.

Thread blight symptoms are noticeable in early summer. Leaves wilt and turn brown (fig. 1), usually on the interior or shaded portions of the tree. Dead, curled leaves cling to blighted branches, frequently mid-branch, with unaffected leaves remaining on both sides of the diseased area (fig. 2). In well-managed orchards, the disease usually does not …

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White Rot of Apple

White rot is often referred to as Botryosphaeria rot or Bot rot and is caused by Botryosphaeria dothidea, a serious fungal pathogen of apple wood and fruit. The fungus causing white rot is ubiquitous in nature, occurring on a wide variety of woody plants, including birch, chestnut, peach, and blueberry. The canker phase of the pathogen can cause considerable loss in many parts of the South, Midwest, and Northeast. Fruit rot infection is most common in areas of the southeastern …

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Wood Rots in Apple Trees

Wood-rotting fungi cause losses over longer periods of time than most other apple diseases. Losses result mainly from breakage of branches and trunks due to a decline in the structural integrity of the wood. Fungal pathogens that colonize wood alter its structural integrity through enzymatic digestion of wood cell wall components. Some of the same fungi that cause wood rot can cause dieback as well.

The two most common symptoms of wood rot are the breakage of limbs or main …

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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 …

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What apple cultivars are resistant or susceptible to 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 throughout the United States wherever apples are grown. 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 …

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What apple cultivars are resistant or susceptible to powdery mildew?

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. More information, complete with images and tables of cultivar susceptibility and resistance, is available in this article on …

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What apple cultivars are resistant to cedar-apple rust?

Cedar-apple rust is a fungus disease of apple and cedar and spends parts of its life cycle on each host. It is caused by Gymnosporangium juniperi-virginianae. The fungus can infect leaves and fruit of most cultivars in the eastern region. A notable exception is ‘Delicious’, which is nearly immune. Find more information and tables of resistant cultivars in this article on Cedar-Apple Rust. 

Answer provided by Alan R. Biggs, West Virginia University.…

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What apple cultivars are resistant or susceptible to bitter rot?

Bitter rot is a fungus disease that causes fruit rot during the summer and preharvest period. The bitter rot fungi are almost worldwide in distribution and cause an especially important disease in the southern areas of the United States. Outbreaks can occur rapidly, and losses can be severe, especially under prolonged warm, wet weather. Several host species can be affected. On peach and nectarine, the same fungus causes a disease known as anthracnose, and on grape it causes ripe rot. …

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What is thread blight, and how do I identify and manage the disease on apple trees?

Thread blight is a fungus disease caused by Corticium stevensii. The disease is primarily a problem in poorly managed orchards in the southeastern United States. Thread blight symptoms are readily noticed in early summer. Leaves wilt and turn brown, usually in the interior or shaded portions of the tree. Dead, curled leaves cling to blighted branches, frequently in mid-branch, with unaffected leaves still appearing on both sides of the diseased area. In well-managed orchards, the disease is usually not …

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