Key Plants and Key Diseases Outdoors

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 ensure the site looks well at all times.

Key diseases (in bold) are those that frequently occur in a plant species. 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.

Plants

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

Reference

Scouting and Controlling Woody Ornamental Diseases in Landscapes and Nurseries

is a 92-page, pocket-sized guide to the key diseases of the key plants noted above. The guide contains 100 color photographs of the key diseases. Cost = $15

Click the link above to order online, or 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.

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