How does Phytophthora affect trees?

Photo: Marta Agostinelli

Phytophthora affects different species of trees and plants in unique ways. It can infect healthy trees, but typically Phytophthora doesn’t kill the tree with a single, fatal blow. Rather, trees suffer with infections to their root system for several years and make way for other microorganisms to become established in the tree. Often, an environmental stressor, such as drought or increasing temperatures, weakens a tree’s vitality and enable Phytophthora present in the soil to become established.

Phytophthora lives in the plant tissue and in soil. Some Phytophthora diseases are spread aerially through wind-dispersed spores, while others that cause soil borne diseases are spread belowground in the soil water. Phytophthora has the capability of surviving periods of harsh climate by forming certain ‘resting’ spores in which they may remain dormant for year until circumstances become better for infection of plants.

When this invasion begins, Phytophthora blocks these fine roots from being able to uptake nutrients and water, which prevents the tree from accessing the food it needs in order to survive. In trees, this process can be gradual or rapid depending on the Phytophthora species involved.

Once the tree loses access to nutrients, it cannot defend itself against other pathogens. The tree is eventually invaded and killed by fungi, insects, or other pathogens that only attack damaged trees.

Photo: Johanna Witzell