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 …
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 …
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.…
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. …
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 …
What is white rot, and how do I identify and manage the disease on apple trees?
White rot is often referred to as Botryosphaeria rot or Bot rot and is caused by Botryosphaeria dothidea, a serious fungal pathogen of apple fruit and wood. The fungus causing white rot is ubiquitous in nature, occurring on a wide variety of woody plants including birch, chestnut, peach, and blueberry. Fruit rot infection is most common in areas of the southeastern United States where losses of up to 50% have been reported. The canker phase of the pathogen can …
What are wood rots in apple trees?
Wood-rotting fungi cause losses over longer periods of time than most other diseases. Losses are caused mainly by breakage of branches and trunks due to a decline in the structural integrity of the wood. Structural integrity of the wood is altered by the enzymatic digestion of wood cell-wall components by the fungal pathogen or pathogens that have colonized the wood. Some of the same fungi that cause wood rot can also cause dieback. Learn more and see images in this …
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 …