Key Landscape Plants and Their Common Diseases: A Monitoring Guide

Selecting the right plants for your landscape and keeping them healthy becomes much simpler when you know which species are prone to disease and what those diseases look like. By identifying key plants—those that frequently develop problems—and the key diseases that affect them, you can focus your monitoring efforts and reduce unnecessary maintenance.

Why Key Plants Matter

Key plants are species that regularly suffer from diseases in the landscape. If your goal is a low-maintenance garden that looks good year-round, avoid planting these high-risk species or be prepared to inspect them routinely. Regular scouting catches problems early, when they’re easiest to manage.

Key Diseases at a Glance

The following list compiles over ten years of records from the Penn State Plant Disease Clinic. Diseases shown in bold are the most frequently observed on each plant; others occur less often but are still worth knowing.

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)

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

Hawthorn (Crataegus)

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

Boston Ivy (Parthenocissus)

• Black rot

English Ivy (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

Pocket Guide for Field Use

Scouting and Controlling Woody Ornamental Diseases in Landscapes and Nurseries

This 90-page, pocket-sized guide covers the key diseases of the plants listed above and includes 109 color photographs for accurate identification. Cost: $7.00 plus shipping and handling.

How to Order:

Call toll-free 877-345-0691 (8:00 a.m.–4:30 p.m., Monday–Friday). All major credit cards accepted. Checks and money orders payable in U.S. currency to Penn State University.

Publications Distribution Center
112 Ag. Administration Bldg.
University Park, PA 16802