Category: Apples

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Rust Diseases – Cedar apple rust and Quince rust

cedar apple rust
Figure 1. Apple rust diseases with cedar apple rust (left) and quince rust (right). Photo courtesy of Penn State University.

Cedar apple rust can infect leaves and fruit of most cultivars in the United States, where the alternate host, Eastern Red Cedar, occurs. A notable exception is ‘Delicious’, which is nearly immune.

The most conspicuous symptoms on apple are bright orange, glistening lesions on the leaves. Lesions which are not inhibited chemically may form small tufts of spore-producing structures (aecia) …

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Sooty blotch and fly speck disease on apple

Sooty blotch and fly speck are caused by a complex of fungal pathogens that commonly appear together as surface blemishes on apple (and pear) in late summer and fall. Although these fungi 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 percent or more are commonly found, even in orchards treated with fungicides. Sooty blotch appears as sooty …

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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 …

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What is the difference between cork spot and bitter pit?

Cork spot and bitter pit are both physiological disorders of apples caused by low levels of calcium.  Visually, cork spots develop anywhere on the fruit, will be relatively small in number per fruit, are sunken and somewhat diffuse spots about 1/2 inch in diameter.  Beneath the spot will be a corky area extending into the flesh of the apple.  Bitter pit, on the other hand, develop only on the half of the apple opposite the stem, are smaller and a …

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What does "low ethylene" apple cultivar mean?

Ethylene is a small gaseous molecule which is present in all plant tissues.  Interestingly, it is a plant hormone and is actively involved in many physiological processes.  One very important process in apples in which ethylene is intimately involved is ripening.  Specifically, ethylene is the triggering molecule for apple ripening.  If ethylene is removed from the fruit or its production is limited within the fruit, ripening will be slowed or, in some cases, nearly stopped.  Low-ethylene cultivars have an inherently …

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What causes mis-shaped apple fruit?

Fruit shape is affected by many factors.  Mis-shapen fruit can result from insect or disease damage.  Tarnished plant bug and plum curculio attack very young fruit.  When that fruit matures, it often develops abnormally. 

Probably, one of the most common causes of mis-shapen fruit is the development of seeds within the fruit.  If seed development is dispersed around the core of the apple, usually the fruit will develop well and symmetrically.  If the seeds develop only on one side of …

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How much should my apple tree grow each year?

The amount of growth an apple tree should produce every year will depend on several factors.  The greatest factor will be the rootstock on which the tree is growing.  Trees on more dwarfing rootstocks will not grow as much as trees on more vigorous rootstocks.  Another major factor is the cultivar of apple being grown. Some cultivars are very vigorous such as Granny Smith compared to  less vigorous cultivars such as Honeycrisp.  Many selections of red delicious are spur-type which …

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Apple Tree Viruses


Virus and Other Graft-Transmissible Diseases and Disorders of Apples

Virus diseases cause economic losses through lower yields and reduced quality of apples and apple products. In general, virus diseases in perennial crop plants, such as apples, are more potentially damaging than in annual crops. Viruses can remain latent, spreading through an orchard and inflicting damage, often without the growers’ knowledge. Latent virus infection can produce small to moderate losses in fruit production. Often growers can maintain the productivity of diseased …

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Apple Rootstock Info: M.7 EMLA

Characteristic Detail Description
Rootstock M.7 EMLA

Formerly known as EM VII. Selected in 1912 from unknown parentage at the East Malling Research station in Maidstone, Kent, England. Trees on M.7 EMLA produce a semi-dwarf tree about 60 to 70% as big as seedling. Trees are moderately precocious and may lean with some cultivars and may require trunk support. Trees tend to produce many rootsuckers. M.7 EMLA has been widely planted since the 1960s with cultivars such as ‘McIntosh’, ‘Empire’, ‘Cortland’,

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Apple Rootstock Info: B.9

Characteristic Detail Description
Rootstock B.9

Resulted from a cross of M.8 x ‘Red Standard’ (Krasnij Standard) from Russia. B.9 has been tested widely and is used commercially in the U.S. In general, B.9 is slightly more dwarfing than M.9 and has slightly higher yield efficiency than M.9. B.9 was selected as a dwarfing cold hardy rootstock and initial inoculation results indicated that it was as susceptible to fire blight as M.9. However, in field trials, trees grafted onto B.9 survived

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