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 diseases are problematic when planting apple trees in heavy soils?
Heavy soils are those that contain more clay particles relative to sand and silt components. The high clay content causes the soils to be less friable, making them “sticky,” and more dense, thus making them hard to work with. They often remain cold and wet in spring and need grit or coarse organic material to admit air and help roots remain healthy. Because of their tendency to be cold and wet for longer periods than lighter soils, there is an …
Which apple rootstocks are susceptible to fire blight?
Consider the relative susceptibilities of the scion and rootstock to fire blight when establishing new orchards. There is considerable variation among apple cultivars (and pear cultivars) in susceptibility to fire blight, although none are immune. Some cultivar/rootstock combinations are so susceptible to fire blight that investments in these combinations are extremely high risk. In the eastern United States, ‘Gala’ on M.26 is an example of a high-risk combination. For more information, read this article on Fire Blight of Apple.…
What is apple scab, and how do I identify and manage the disease?
Apple scab is a fungus disease caused by Venturia inaequalis. It is of major economic importance and, if not controlled, the disease 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. For more information, read this article on Apple Scab.
Answer provided by Alan R. Biggs, West Virginia University.…
What is southern blight in apple trees?
Southern blight is caused by the fungus 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. For more information, read this article on Southern Blight in Apple Trees.
Answer provided by Alan R. Biggs, West Virginia University.…
What is cedar-apple rust, and how do I identify and manage the disease?
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. For more information, see this article on Cedar-Apple Rust.
Answer provided by Alan R. Biggs, West Virginia University.…
What is white root rot in apple trees?
White root rot, caused by the fungus Scytinostroma galactinum (formerly Corticium galactinum), has been known as a parasite of apple trees for many years and is widely distributed (Canada to Texas and westward to the Pacific Coast, Europe, West Indies, and Japan). It is found in both bearing and non-bearing apple orchards. Other hosts include a wide variety of woody plants, ornamental shrubs, and herbaceous perennials, including white pine, ash, peach, blackberry, dewberry, Japanese wineberry, dogwood, sumac, white campion, …
What is apple mosaic virus, and how do I identify and manage the disease?
Apple mosaic virus is one of the oldest known and most widespread apple viruses. The same virus can cause line pattern symptoms in plum and rose mosaic disease. Apple mosaic virus is related to Prunus necrotic ringspot virus. Apple trees infected with apple mosaic virus develop pale to bright cream spots on spring leaves as they expand. These spots may become necrotic after exposure to summer sun and heat. Most commercial cultivars are affected but vary in severity of symptoms. …
What is bitter rot, and how do I identify and manage the disease?
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 economically 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 …
What is blue mold, and how do I identify and manage the disease?
Blue mold is a fungus disease caused by Penicillium expansum. It is the most important postharvest decay of stored apples in the United States. The losses from this disease can be significant but can be substantially reduced by following proper sanitation and control measures. The fungus not only causes fruit decay but also produces the carcinogenic mycotoxin patulin. This toxin may rise to unacceptable levels in fruit destined for processing and may also result in off flavors. For more …