Key Plants and Key Diseases Outdoors
Gary W. Moorman, Professor of Plant Pathology
Selecting plants for placement in the landscape as well as monitoring them for diseases and planning appropriate disease management strategies can be simplified if the key plants in the landscape are known and if the key diseases on those plants can be identified. KEY PLANTS, ones that frequently have diseases, should be monitored on a regular basis. Key plants should not be used in the landscape if one goal at the site is to minimize the amount of maintenance work required to assure the site looks well at all times. KEY DISEASES (in bold) are those that frequently occur on the plants. The other diseases listed sometimes occur. The following list of key plants and their key diseases was compiled from over 10 years of records from the Penn State University Plant Disease Clinic.
Scouting and Controlling Woody Ornamental Diseases in Landscapes and Nurseries is a 90 page, pocket-sized guide to the key diseases of the key plants noted above. The guide contains 109 color photographs of the key diseases. It can be purchased from
|Ash (Fraxinus)||Hawthorn (Crataegus)|
|Cedar-quince and cedar-hawthorn rusts|
||Ivy, Boston (Parthenocissus)|
|Botrytis blight||Black rot|
|Ovulinia flower blight|
|Cherry (Prunus)||Ivy, English (Hedera)|
|Bacterial leaf spot||Colletotrichum leaf spot|
|Black knot||Bacterial leaf spot|
|Coccomyces leaf spot|
|Crabapple (Malus)||Juniper (Juniperus)|
|Cedar-apple rust||Cedar-apple, hawthorn and quince rusts|
|Fire blight||Kabatina twig blight|
|Powdery mildew||Phomopsis twig blight|
|Dogwood (Cornus)||Lilac (Syringa)|
|Anthracnose||Bacterial leaf blight|
|Septoria leaf spot||Powdery mildew|
|Powdery mildew||Witches broom|
|Elm (Ulmus)||Oak (Quercus)|
|Dutch elm disease||Bacterial leaf scorch|
|Black leaf spot||Leaf blister|
|Phloem necrosis (yellows)|
| Pachysandra (Pachysandra)
| Volutella blight
Publications Distribution Center
112 Ag. Admin. Bldg.
University Park, PA 16802
$7.00 (includes postage and handling). Make checks payable to Penn State University.
Notice: The user of this information assumes all risks for personal injury or property damage.
Warning! Pesticides are poisonous. Read and follow all directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams or ponds.
Issued in furtherance of Cooperative Extension work, Acts of Congress, May 8 and June 30, 1914, in cooperation with the U. S. Department of Penn State College of Agricultural Sciences research and extension programs are funded in part by Pennsylvania counties, the Commonwealth of Pennsylvania, and the U.S. Department of Agriculture.
Visit Penn State Extension on the web at extension.psu.edu.
Where trade names appear, no discrimination is intended, and no endorsement by Penn State Cooperative Extension is implied.
This publication is available in alternative media on request.
The Pennsylvania State University is committed to the policy that all persons shall have equal access to programs, facilities, admission, and employment without regard to personal characteristics not related to ability, performance, or qualifications as determined by University policy or by state or federal authorities. It is the policy of the University to maintain an academic and work environment free of discrimination, including harassment. The Pennsylvania State University prohibits discrimination and harassment against any person because of age, ancestry, color, disability or handicap, national origin, race, religious creed, sex, sexual orientation, gender identity, or veteran status. Discrimination or harassment against faculty, staff, or students will not be tolerated at The Pennsylvania State University. Direct all inquiries regarding the nondiscrimination policy to the Affirmative Action Director, The Pennsylvania State University, 328 Boucke Building, University Park, PA 16802-5901; Tel 814-865-4700/V, 814-863-1150/TTY.