MSU Extension

Flowering crabapples are among the most popular ornamental trees. Few woody plants offer so many all-season values as these trees.

This easy-to-use guide can help you select the crabapple best suited for your planting site. Eighty-five species and cultivars are listed, with information on disease resistance and ornamental traits—size, shape and color of flowers and fruit. Also included are helpful tips on which typed of tree to plant in certain areas of your landscape.

Crabapple Selection Criteria

(Courtesy of John J. Sabuco, landscape architect and president of the Internal Ornamental Crabapple Society.)

Selecting Crabapples for the Landscape

To select a good crabapple tree, look for desirable ornamental traits plus the least amount of disease susceptibility.

R=Round
U=Upright (Narrow)
W=Weeping
U=Upright (Spreading)
S=Shrub

Ornamental Traits

Flowers

In the spring, the showy blossoms make their appearance before the lilacs bloom. Although the actual time of bloom will vary from year to year, depending on temperature, a total blom period of up to four weeks can be expected. Very-early blooming crabapples may flower as early as the star magnolia, while late bloomers may coincide with the black locust. The bloom period of an individual cultivar may vary from two days to almot two weeks depending on weather conditions.

Crabapple buds may be pink, white or red, and open blossoms may be white to dark purplish red, with many variations in between. Most crabapples have single flowers, but a few have semi-double or double blossoms.

Some cultivars bloom heavily only every other year. Avoid these alternate-bearing trees. The majority of crabapple cultivars produce consistent flower displays each year.

Foliage

Most crabapples have attractive green foliage. Some have a distinct reddish or bronze leaf color for the first month or so of the growing season. Most crabapple cultivars do not have especially attractive fall colors.

Fruits

A flowering crabapple is defined as any apple (genus Malus) with fruit 2 inches or less in diameter. The color of the ¼- to 2-inch fruits ranges from bright red to purple and bright yellow to orange, with intermediate shades and combinations. Fruits of some cultivars begin to color in August, while the fruits of others do not reach their true color until September or October.

The fruits of some cultivars ripen and drop by the end of August, but the fruits of others may still be present in the spring. Cultivars with fruits persisting into winter can add a good deal of color to the eaerly winter landscape. Birds may eat these fruits in winter.

Fruits follow the flowers, so alternate-bearing cultivars will fruit heavily only in those yhears when they produce many flowers.

Growth Habit

Flowering crabapples can be less than 20 feet tall, but some may grow to 30 or 40 feet. Most crabapples are rounded and dense, but growth habit varies widely from narrowly upright to weeping. In summer, each form of crabapple lends a distinctive character to the landscape, and the twisted limbs of older specimens add a picturesque beauty to the winter scene. The various plant forms, flowers and fruit colors make crabapples a very useful species in the landscape.

Diseases

Disease susceptibility or resistance should be given as much consideration as the ornamental traits when selecting a crabapple. Four diseases—apple scab, fire blight, cedar-apple rust and powdery mildew—are the major disease problems affecting crabapples.

Apple Scab

Apple scab causes the leaves to turn yellow and drop prematurely in mid- to late-summer. The fruits will usually have sunken, corky, dark olive areas.

This fungal disease attacks many species, including crabapple, apple, mountain ash, pear, pyracantha and quince. The disease in some years can completely cover leaves of susceptible cultivars. Such sever infections, referred to as “sheet scab,” will defoliate an entire tree. The loss of infected leaves weakens the tree. Scab can defoliate a tree several times in one season.

The scab fungus forms two types of spores. The first type is formed on fallen leaves of the previous year and is blown about in the wind. It causes the first infections in the spring. These infections form a second type of spore that is spread by rain splash and infects only the same plant or nearby plants of the same species. The more rainy the season is, the more the disease spreads throughout adjacent plants.

If you can prevent the first type of spore from infecting the plant in early to midspring, the plant will escape further infections htat season.

This disease is not fatal but requires regular sprays from bud-break through mid-June. Fungicides labeled for use on crabapple for scab include chlorothalonil (Daconil 2787) and benomyl (Benlate). Apply a fungicide when swollen flower buds show one-half inch of green tissue. Follow withapplications, as needed, to protect the plant throughout the blooming period whenever dew or rain threatens to wet leaves for 6, or more, hours.

Cultural controls include raking and burning fallen leaves before spring and replacing highly susceptible cultivars with resistant cultivars.

Fire Blight

Fire blight is a bacterial disease that causes leaves to blacken and hang on the tree. As the bacteria spread to larger branches, more of the tree dies and the bark of infected branches becomes wrinkled and peels. This disease is usually fatal—there is no effective chemical control. Shoots often have bent, drooped tips and resemble a shepherd’s crook.

Bacteria generally cause blights during wet weather in early spring when buds are breaking. Warm spring weather favors fire blight on crabapples.

In wet spring weather, cankers formed during previous infections ooze droplets of bacteria. The bacteria are splashed by rain and blown about as mists, or insects may visit the attractive ooze and carry it about. infections usually begin either through nectaries of flowers or through the microscopic pores (stomates) in leaves.

Avoid using high-nitrogen fertilizers on susceptible cultivars. Such fertilizers can increase susceptibility to fire blight.

Cedar-Apple Rust

Cedar-apple rust is aptly named—it causes rust-colored spots on the leaves. In late summer, brownish clusters of threads or cylindrical tubes appear beneath the yellow leaf spots, or on fruits and twigs. The spores formed in the threads or tubes infect the leaves and twigs of junipers during wet, warm weather in late summer and early fall.

Galls and swellings on the junipers appear about seven months later and form gelatinous masses of spores after about 18 months. Rust is very conspicuous red cedar and other junipers during spring when the galls are covered with the orange-brown, gelatinous masses. Rust spores formed on the junipers can not affect other junipers but will infect twigs and leaves of crabapples. The galls on junipers will produce spores for only one year. The gelatinous masses are usually seen in the spring, after a period of warm, rainy weather.

This problem is less serious than the previous two and can be controlled with fungicides. Chlorothalonil (Daconil 2787) is labeled for controlling rust.

Cultural controls include getting rid of nearby junipers and planting resistant crabapples cultivars.

Powdery Mildew

Powdery mildew is the least serious of the four diseases. The white, powdery coating on the leaves may not be seen in most years. This is the only fungal disease in which the fungus grows on the surface of the plant. There it forms a superficial, white, powdery coating on leaves, buds, shoots and flower petals. The entire leaf surface may be covered with a cottony spider webbing, most of which consists of spores ready to be blown to uninfected leaves. The fungus can easily be wiped off the surface.

Powdery mildew is a disease of mid-to late-summer. It is most serious in shady, damp locations where plants are crowded, air circulation is poor and relative humidity is high. Powdery mildews flourish when days are warm and nights are cool, and when dew forms on the leaves.

The disease is easily controlled with fungicides such as benomyl (Benlate) or lime-sulfur.

Ornamental Traits and Susceptibility to Diseases of Crabapple Species and Cultivars

The table below lists crabapple species and cultivars and shows their ornamental traits and apple scab susceptibility. To use “Flower” column: The left side lists the color of the flower bud to the left of the slash (/) mark and the color of the open flower to the right. The part of the column indicates whether the flowers are single (sgl) or double (dbl).

Form Codes
P=Pyramidal
R=Round
S=Spreading
U=Upright
W=Weeping

Apple Scab Codes

PA= Ratings from Pennsylvania State University
        Ratings are from 1985. Ratings are SL=slight, M=moderate, SV=severe, VS=very severe
        Ratings were not defined in terms of how trees looked.

IL= Ratings from Morton Arboretum
       Ratings are for 1986. Ratings are SL=slightly susceptible, M=moderately susceptible, SV=severely susceptible, VS=very severely susceptible, NS=not susceptible.
        Ratings are the worst observed under conditions that best promote the disease.

OH= Ratings from Ohio State University
         Ratings listed are the worst rating for the four years 1983-1986.
         Rating system used is HR=highly resistant—no indication of disease; R=resistant—mild infection with no defoliation; S=susceptible—medium infection with only slight defoliation; HS=highly susceptible—heavy infection often accompanied by considerable defoliation.

MI= Ratings from Michigan State University
        The ratings listed are for 1976. The rating scale is R=resistant, T=tolerant (leaves become infected but no defoliation), S=susceptible (trees are defoliated).

Form Codes
P=Pyramidal
R=Round
S=Spreading
U=Upright
W=Weeping

Apple Scab Codes

PA= Ratings from Pennsylvania State University
        Ratings are from 1985. Ratings are SL=slight, M=moderate, SV=severe, VS=very severe
        Ratings were not defined in terms of how trees looked.

IL= Ratings from Morton Arboretum
       Ratings are for 1986. Ratings are SL=slightly susceptible, M=moderately susceptible, SV=severely susceptible, VS=very severely susceptible, NS=not susceptible.
        Ratings are the worst observed under conditions that best promote the disease.

OH= Ratings from Ohio State University
         Ratings listed are the worst rating for the four years 1983-1986.
         Rating system used is HR=highly resistant—no indication of disease; R=resistant—mild infection with no defoliation; S=susceptible—medium infection with only slight defoliation; HS=highly susceptible—heavy infection often accompanied by considerable defoliation.

MI= Ratings from Michigan State University
        The ratings listed are for 1976. The rating scale is R=resistant, T=tolerant (leaves become infected but no defoliation), S=susceptible (trees are defoliated).

Other Publications

There are many other publications about ornamental plants available from your Cooperative Extensive Service at Michigan State University. Just visit your county office for a copy of these bulletins, or write to:

MSU Bulletin Office
Michigan State University
10-B Agricultural Hall
East Lansing, MI 48824-1039

Listed below are some of the available publications that may be of interest to you.

E-786, Fertilizing Shade and Ornamental Trees (85c)
E-804, Pruning Shade and Ornamental Trees (35c)
E-1818, A Gardener’s Guide to Shrubs ($3.00)
E-1936, Selecting Ornamental Plants for Michigan Landscapes (Single copy free to Michigan residents)
E-1947, Planning and Care of Ornamental Landscape Plants (35c)
E-1984, Growing Perennial (30c)
E-2024, Diagnosing Problems of Ornamental Landscape Plants (65c)