Aboveground symptoms of Phytophthora root rot are typical of plants with a weak root system; infected plants are slow growing and may wilt or die in hot weather. Roots may have water-soaked injured areas that gradually dry and turn chocolate brown as the disease progresses.
Life cycle
Phytophthora is a soil-inhabiting fungus that is favored by wet conditions. Species of Phytophthora produce resting spores that survive for years in moist soil in the absence of a suitable host. When a host is nearby and free water is present in the soil, resting spores germinate to produce motile spores that can directly penetrate roots, branches, or crowns as long as free water is present. Resting spores, decaying host tissue in the soil, and active cankers can all be sources for new infections. The fungus can be spread in splashing rain or runoff water and by the movement of contaminated soil or plant parts. Root rot of avocado, citrus, and tomato is favored by warm conditions; decay of crown, trunk, and branches of other tree species is favored by cool, wet conditions.
Solutions
Avoid prolonged saturation of the soil or standing water. Provide good soil drainage. Raised beds provide good drainage in gardens.
For more information, see the Phytophthora Root and Crown Rot Pest Note.
