Key Plants and Key Diseases Outdoors

Selecting plants for placement in the landscape can be simplified if the key plants are known and if the key diseases on those plants can be identified.
Key Plants and Key Diseases Outdoors - Articles


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 Plant Disease Clinic.


Ash (Fraxinus)

  • Anthracnose

Azalea (Rhododendron)

  • Botrytis blight
  • Leaf gall
  • Ovulinia flower blight
  • Powdery mildew
  • Root rots

Cherry (Prunus)

  • Bacterial leaf spot
  • Black knot
  • Coccomyces leaf spot

Crabapple (Malus)

  • Cedar-apple rust
  • Fire blight
  • Powdery mildew
  • Scab

Dogwood (Cornus)

  • Anthracnose
  • Septoria leaf spot
  • Powdery mildew

Elm (Ulmus)

  • Botryodiplidia canker
  • Dutch elm disease
  • Black leaf spot
  • Phloem necrosis (yellows)
  • Wetwood

Hawthorn (Crataegus)

  • Fire Blight
  • Leaf spot
  • Cedar-quince and cedar-hawthorn rusts

Ivy, Boston (Parthenocissus)

  • Black rot

Ivy, English (Hedera)

  • Colletotrichum leaf spot
  • Bacterial leaf spot

Juniper (Juniperus)

  • Cedar-apple, hawthorn and quince rusts
  • Kabatina twig blight
  • Phomopsis twig blight
  • Root rot

Lilac (Syringa)

  • Bacterial leaf blight
  • Powdery mildew
  • Witches broom

Oak (Quercus)

  • Anthracnose
  • Bacterial leaf scorch
  • Leaf blister

Pachysandra (Pachysandra)

  • Volutella blight


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. Cost = $7

How to Order:

call toll-free 877-345-0691 from 8:00 a.m. to 4:30 p.m., Monday through Friday We accept all major credit cards, including MasterCard, VISA, Discover, and American Express. Checks and money orders payable in U.S. currency are also accepted.

Publications Distribution Center
112 Ag. Administration Bldg.
University Park, PA 16802
$7.00 (plus shipping and handling).
Make checks payable to Penn State University.