Plant Disease Management Handbook

Use of Disinfestants to Control Plant Pathogens

Cause There are several different root rot causing organisms occur on Viburnum with Phytophthora spp. and Rhizoctonia sp. being found most often. These soil-borne pathogens initially infect small feeder roots, and then spread to the main roots. Plant crowns may be invaded if conditions remain conducive for spread.

Cause Sphaerotheca sp. has been reported in Oregon and found a few times by the OSU Plant Clinic. This is a highly specialized pathogen that form a close association with the host. Conditions that favor the host also tend to favor the pathogen. The disease is favored by low light, warm conditions (60°F to 80°F) and cool nights. Overcrowding of plants is also favorable for disease development.

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Cause Peronospora grisea, a fungus-like organism. Moist or very humid conditions favor sporulation and disease development. Spores are dispersed by wind and splashing water. Spores germinate and infect when free water is present on the leaves.

Top and bottom of a leaf

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By C. M. Ocamb

By C.M. Ocamb