Phytophthora multivora

Phytophthora multivora is a soil-borne oomycete pathogen notorious for causing devastating root rot, collar rot, and dieback in a wide range of woody hosts. It is recognized as a significant threat in forestry, horticulture, and plant nurseries due to its wide host range and ability to thrive in various environmental conditions.

Common host species include the European beech (Fagus sylvatica), various eucalyptus species, several conifers, and numerous ornamental shrubs. The pathogen is particularly destructive in nurseries, where it can cause high mortality rates in young seedlings, leading to significant economic losses for commercial growers.

Symptoms typically begin at the root level, where the pathogen destroys the fine feeder roots, preventing the plant from absorbing water and nutrients. Above-ground signs include progressive yellowing of leaves (chlorosis), stunted growth, necrotic lesions on the root collar, and eventually dieback of branches, which can lead to the total collapse of the tree.

The development of the disease is heavily dependent on soil moisture levels and temperature. Phytophthora multivora thrives in water-saturated soils and moderate temperatures, which facilitate the production and motility of zoospores. These zoospores swim through soil water films to infect new roots, while resistant chlamydospores allow the pathogen to persist in the soil for years.

Management and prevention involve a combination of cultural and chemical practices. Growers should prioritize the use of certified, disease-free planting material, ensure optimal soil drainage, and strictly sanitize all equipment between sites. Fungicides containing active ingredients such as fosetyl-aluminium or metalaxyl-M can provide protection, but they are most effective when integrated into a comprehensive management program aimed at reducing the pathogen population.