Pine: Phytophthora root rot

categories: Conifers Ornamentals Pine Pine Diseases

revision date: 2023-02-07 12:00

Reddish-brown discoloration in trunk from Phytophthora root rot infection.
Phytophthora root rot damage to trunk
Photo by: R.S. Byther

Biology

Phytophthora root rot is usually a problem only in areas with poor drainage or where flooding occurs. The fungus attacks the roots, which rot and die. The infection moves up into the crown, where the cambium (soft inner bark) turns reddish-brown instead of the normal greenish-white. Older trees may develop cankers on the trunk, possibly accompanied by split bark and oozing pitch. Lower branches wilt, turn brown, and die back. Younger trees are often killed outright, while infected mature trees may show wilting, branch dieback, or other signs of inhibited water and nutrient uptake. Phytophthora root rot on pines is mainly a problem in nurseries or other irrigated plantings.

Management Options

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

  • Prevent disease by planting only disease-free materials in noncontaminated soil.
  • Improve soil drainage by incorporating organic material or using raised beds.
  • Avoid soil compaction, which reduces drainage. Construction, heavy foot traffic, or machinery can cause soil compaction.
  • Remove and destroy all infected plants and plant debris.
  • Plant resistant species in infected areas. Pinus mugo var. mughus has been found resistant to Phytophthora cinnamomi and P.¬†lateralis. Your county Extension agent or WSU Master Gardeners can provide additional information found in the PNW Disease Management Handbook.

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.

  • None recommended