Dolgo Crabapple - Malus 'Dolgo' [2]
Rose Family: Rosaceae
Dolgo crabapple is particularly resistant to apple scab, and is grown for its large edible fruits. [4]
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  Dolgo Crabapple Tree
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Crabapples are versatile, small, ornamental trees used in the urban landscape. Crabapples bloom in spring, usually in May, bearing flowers that vary a great deal in color, size, fragrance ,and visual appeal. It is common for flower buds to be red, opening to pink or white flowers. The fruit ripens between July and November, and varies in size from ¼ to 2 inches long or wide. Dolgo crabapple is favored due to its disease resistance.
 
Dolgo Crabapple Trees
Dolgo Crabapple, Morton Arboretum acc. 108-84*2 is 25 years old [2]

Dolgo crabapple requires very little pruning but any that is needed should be completed before late spring, to ensure dormant flower buds are not removed. Trees used as street trees should be trained to develop a central trunk and should be occasionally thinned to eliminate water sprouts or crossed-branches, and to open up the crown. This allows for better air circulation through the crown and helps reduce disease.

Crabapples are useful as median trees where the fruit will not fall on pedestrians. Placed in the lawn area as an accent so they receive occasional irrigation, Dolgo crabapple will give you years of wonderful flowers and showy fruit. It is best to locate them away from a patio or other hard surface so the fruits will not cause a mess. Set it back just far enough so the crown will not overhang the walk, but close enough so the flowers and fruit can be enjoyed. Dolgo crabapple grows in moist, well-drained, acid soil in full sun locations for best flowering. They are not recommended for sandy soil due to their inability to tolerate drought, but any other soil is suitable, including some clay.  [1]

Dolgo crab blossoms and foliage

In selecting a crabapple variety, disease resistance should be the first consideration. There are four principle diseases of plants in the rose family:

Apple scab is one of the most serious diseases from an aesthetic standpoint. Caused by the fungus Venturia inaequalis, which develops in cool, wet springs, scab is usually not life-threatening.  Dolgo crab is one among numerous cultivars that are resistant or very tolerant (still susceptible but with little defoliation). Apple scab causes spotting of the leaves, premature defoliation, and unsightly spots on the fruit. Apple scab affects members of the rose family, including nearly all cultivars of apple, crabapple, hawthorn, mountain-ash, cotoneaster, firethorn, and common pear. [4]

Cedar-apple rust is a leaf-spotting disease common to many plants in the rose family when planted near plants in the Family Cupressaceae (Cypress, Arborvitae, Juniper), which serve as host for the fungus Gymnosporangium juniperi-virginianae.  Woody galls form on branches and spring shoots; gelatinous, orange spore-producing bodies emerge from the growths. Orange spots may also appear on the foliage. [5]

Powdery mildew is a fungal disease that can cause considerable damage to leaves and fruit of susceptible cultivars without threatening the health of the tree. Poor air circulation, close association with susceptible apple cultivars, and wet, humid weather conditions will greatly influence disease incidence and severity.

Fire blight,  caused by the bacterium Erwinia amylovora, is a common and frequently destructive bacterial disease of pome fruit trees and other rose family plants. Pear and quince are particularly susceptible. Apple, crabapple, and Pyracantha species are also frequently damaged. Fire blight occasionally attacks hawthorn, Spiraea, Cotoneaster, Juneberry and serviceberry, and mountain ash. Fire blight infections can destroy limbs and even entire shrubs or trees. [3]
 

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References
  1. USDA National Forest Service Fact Sheet 393, Malus x 'Mary Potter'
  2. Dolgo Crabapple, Morton Arboretum accs. 108-84*1 & 2, photographed by Bruce Marlin
  3. B. L. Teviotdale,  UC ANR Publication 7414, Pest Notes "Fire Blight"
  4. Morton Arboretum, Apple Scab
  5. Cornell University, "Cedar-apple Rust"

 

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