Disease Control in the Landscape

Bulletin 614

Chapter 5

Disease-Resistant Varieties

The use of plant species or varieties that are genetically resistant to diseases is probably the most effective means of controlling plant disease. Unfortunately, many of the plants that are common in Ohio's landscapes do not have resistance to many of the more common diseases; however, when disease resistance combined with suitable horticultural characteristics is available, it should be used as an integral part of the disease management program.

The species or cultivar planted often determines whether certain diseases are likely to develop or can be avoided. Resistant varieties either cannot be infected by certain pathogens or are not seriously damaged if they do become infected. Landscape plants with resistance to certain diseases are listed in Tables 2-7. When appropriate, notes on disease resistance are provided in the section on general and specific diseases.

Check with the Ohio State University Extension office in your county or a certified nursery person for the most recent recommendations and use the information provided here to choose resistant species and varieties that are well suited to local conditions. If you select a more susceptible variety because of other preferred horticultural characteristics, be prepared to accept disease damage or devote the effort and resources required to manage it.

A very useful resource for information about disease and insect resistance in ornamental plants is: Pest Resistant Ornamental Plants by Deborah C. Smith-Fiola, Rutgers Cooperative Extension. This publication lists ornamental landscape plant cultivars and varieties that have been documented to be resistant to specific insects and diseases. The cost is $7.00 plus $1.70 for postage (total cost $8.70). Multiple copies can be obtained at less expensive rates. Contact the following address for further information:

Rutgers Cooperative Extension
1623 Whitesville Rd
Toms River, NJ 08755-9720
Phone: (908) 349-1246.

Crabapples and Disease Resistance

Crabapples are very popular ornamental plants for landscapes, commercial settings and parks and arboreta in Ohio. One potential problem with certain crabapples is infectious disease problems such as apple scab, fireblight, frogeye leaf spot, and occasionally cedar rusts, powdery mildew, and others.

There are hundreds of crabapple species, cultivars, varieties, and selections. Following are descriptions of some of the crabapples rated highly in Ohio for both overall ornamental aesthetics and overall disease resistance in recent years*. This list is not comprehensive. (These ratings for Ohio may differ in other locations due to greater disease pressure, for example, fireblight in certain mountain states, or the presence of localized races of pathogens.)

Some Suggested Crabapples for Ohio

• Malus baccata (Jackii)--Maroon-red fruits. White flowers. Glossy, green foliage is exceptional ornamental feature. Handsome rounded form and structure. Grows to 30 feet tall and 25 feet wide. Excellent overall disease resistance.

• Bob White--Yellow to gold fruits. White flowers. Broadly rounded crown. Grows to 20 feet tall and 20 feet wide. Tremendous show of delicate white flowers in spring and small golden fruits in fall and winter months. Excellent overall disease resistance.

• Donald Wyman--Bright red fruits. White flowers. Lustrous green foliage. Attractive flaking bark. Rounded tree grows to 20 feet in height and 20 feet in spread. Fruits held persistently well into the winter months. Some scab susceptibility, but not a detraction in most years.

• Mary Potter--Red fruits. White flowers. Attractive bark. Spreading-weeping habit, with ultimate height of 15 feet and width of 20 feet. Trace of scab and slight fireblight incidence, but overall good disease resistance.

• Molten Lava--Red-orange fruits. White flowers. Fruits and yellowing fall foliage provide a fiery cascading image. Weeping-spreader with multilayered overlapping branches providing fine winter effect. Height of 12 feet and width of 15-foot spread. Some scab but not a factor ornamentally in most years.

• Prairifire--Red-purple fruits. Coral-red flowers. Dark green leaves are tinged with red-purple. Flower and fruit show is outstanding. Rounded, airy growth habit with height of 20 feet and width of 20 feet. Excellent overall disease resistance.

• Red Jade--Red fruits. White flowers. Spreading, weeping habit is attractive year-round feature in the landscape. Height of 15 feet and width of 15 feet. Some scab but not ornamentally detracting in most years.

• Red Jewel--Cherry-red fruits. White flowers. Small growth habit. Fruit persists well into the winter months. Height of 15 feet and width of 12 feet. Excellent disease resistance.

• Malus sargentii--Red fruit. White flowers. Attractive low-spreading growth habit is an excellent feature, especially as plant ages. Very effective in group plantings. Height of 8 feet and width of 16 feet. Excellent disease resistance.

• Sentinel--Red fruits. White with pink-tinged flowers. Pink buds opening to white flowers are sensational. Vase-shaped upright habit. Height of 15 feet and width of 10 feet. Trace of scab but not detracting ornamentally.

• Strawberry Parfait--Fruits mostly red with yellow base. Pink flowers with red margins. Unusual erratic upright-spreading growth habit is one of its best features. Height of 20 feet and width of 25 feet. Fruits remain firm into the winter months. Foliage is striking as it develops along the upright branches in the spring. Excellent disease resistance.

• Sugar Tyme--Brilliant red fruits. White flowers. Broadly rounded growth habit with a height of 18 feet and width of 15 feet. Prolific, showy fruits persist long into the winter months. Trace of scab but not detracting ornamentally in most years.

* For more information on aesthetic and disease resistance evaluations of crabapples in Ohio, see yearly evaluation summaries in publications such as: Ornamental Plants, Annual Reports and Research Summaries, 1995 and 1996. Ohio Agricultural Research and Development Center Special Circulars 152 and 154.