Sunday, December 6, 2015

Phytophthora Root and Crown Rot

Some species of soil-inhabiting pathogens in the genus Phytophthora, which means "plant destroyer", cause root and crown rot diseases of herbaceous and woody plants.  According to UC IPM, "Almost all fruit and nut trees, as well as most ornamental trees and shrubs (including many California natives), can develop Phytophthora rot.During the first half of 2015 thirty-three Phytophthora species were identified in container stock samples from twenty nurseries.  Seventy-five percent of the participating nurseries tested positive for at least one Phytophthora species.  Detection has also occurred in native habitat restoration areas with devastating effect.  Since inadvertent inoculation of native habitats by Phytophthora-infected nursery stock could severely impact wildlands, the native plant community is leading the battle.  A "Working Group for Phytophthoras in Native Plant Habitats" has formed to better understand Phytophthora and develop best management practices to minimize the spread of disease.  "In general, Phytophthora (now considered a water mold or oomycete) requires warm, moist  soils in order to cause disease.  The gardener will reduce the threat of Phytophthora by avoiding prolonged saturation of the soil.  Irrigate only as much and as often as necessary.  If using a drip system, place the emitters at least a foot away from the trunk.  Avoid planting susceptible species on poorly drained or shallow soils." - UC IPM

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