What is Phytophthora root rot? Phytophthora root rot is the most serious root disease of American ginseng (Panax quinquefolium) in Wisconsin. Left untreated, this disease can totally destroy a ginseng crop during a typical three to four year production cycle.
What does Phytophthora root rot look like? Ginseng plants with Phytophthora root rot show signs of wilting, often combined with a reddish discoloration in their foliage. Roots of affected plants are tan and watery, and often disintegrate when handled. Infected roots often also have a pungent, bitter, earthy odor. Where does Phytophthora root rot come from? Phytophthora root rot is caused by Phytophthora cactorum, a common soil fungus. This fungus is most active during wet periods, particularly during May and early June in Wisconsin. However Phytophthora root rot can occur anytime during the growing season. How do I save ginseng with Phytophthora root rot? Once a ginseng plant has been infected by Phytophthora cactorum, little can be done to save the plant. If infected plants occur in patches, attempt to localize the area by carefully removing a 1 to 2 ft. wide swath of healthy plants, about 5 ft from the edges of the affected area. How do I avoid problems with Phytophthora root rot? Site selection and maintenance are critical for control of this disease. Select a site with topography and a soil type that ensures good drainage, and plan gardens so that older gardens DO NOT drain into younger gardens. In wetter sites, dig trenches to drain standing water. Also, DO NOT move soil or plant material from an infested garden into a non-infested garden. Disinfect tools, boots and spray equipment with a 10% bleach or detergent solution when moving from garden to garden. Fungicide treatments are also important for management of Phytophthora root rot. A combination of Ridomil Gold GR and Aliette WDG provides the best control and should help prevent the development of fungicide-insensitive strains of Phytophthora cactorum. For more information on Phytophthora root rot: Contact your county Extension agent.
© 2019 the Board of Regents of the University of Wisconsin System doing business as University of Wisconsin-Madison Division of Extension.
An EEO/Affirmative Action employer, University of Wisconsin-Madison Division of Extension provides equal opportunities in employment and programming, including Title IX and ADA requirements. This document can be provided in an alternative format by calling Brian Hudelson at (608) 262-2863 (711 for Wisconsin Relay).
References to pesticide products in this publication are for your convenience and are not an endorsement or criticism of one product over similar products. You are responsible for using pesticides according to the manufacturer’s current label directions. Follow directions exactly to protect the environment and people from pesticide exposure. Failure to do so violates the law.
Thanks to Mike Drilias and Ann Joy for reviewing this document.
A complete inventory of University of Wisconsin Garden/Farm Facts/Pest Alerts is available at the University of Wisconsin-Madison Division of Extension Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.