University of Illinois Extension

University of Illinois Extension

Hort Answers

Fungal Disease

Phytophthora Canker, Basal Rot, & Root Rot [Shrubs and Trees]
Phytophthora spp. [water molds]

Phytophthora basal rot of Rhododendron.
Phytophthora basal rot of Rhododendron.
2.5 (1 = rare 5 = annual)
4.5 (1 = very little damage 5 = plants killed)

Some Phytophthora spp. attack a very narrow range of host plants while others may attack a very wide range of host plants. Overall, Phytophthora attacks a wide range of plants growing in poorly drained soils or in over watered soils. Phytophthora spp. are the most common root rot pathogens found on woody plant material. It causes crown or collar rot on apple, dogwood, rhododendron, cherry, yew, hemlock, pine, and fir. On beech, birch, maple, dogwood, and sweet gum, it causes bleeding canker.

NOTE: Phytophthora ramorum is a relatively new and destructive disease affecting additional plants and has become established in parts of some western states.

Plants Affected
As roots rot and die, stunting, poor growth, early fall coloration, dieback, wilt and eventual death occur. Discoloration of the inner bark and wood at the base of the infected plant is usually present and visible if the outer bark is scraped away. There is a distinct margin between healthy and diseased crown tissues. Reddish-brown liquid may exude from the cankered area (hence, the name "bleeding canker"). Laboratory diagnosis is necessary to confirm the presence of Phytophthora because other root problems mimic the above-ground symptoms of this disease.

Life Cycle
Phytophthora is a soil-inhabiting fungus-like organism that requires high moisture to complete its life cycle. Therefore, the disease is most common under conditions of saturated soils. The pathogen might initially invade small roots as well as crown tissue. The pathogen is spread by movement of contaminated soil or diseased plants or by splashing water.

Correct the drainage, cut back on watering and wait a couple of growing seasons before replanting. Or, correct the drainage, change watering practices and perhaps treat the soil with a recommended soil fungicide. If the drainage problem is corrected before the plant declines too much, the plant may recover. During recovery, the plants are prone to other diseases.

Related Resources
Home, Yard & Garden Pest Guide
Illinois Commercial Landscape and Turfgrass Pest Management Handbook
U of IL - Distance Diagnosis through Digital Imaging
U of IL - Plant Clinic