Phytophthora Root Rot

Phytophthora sp.

Phytophthora overwinters in the soil. Extended periods of high

soil moisture lead to infection. The sporangia cause infections by germinating directly and colonizing roots or by releasing zoospores into water. Wounded roots are easily infected. Phytophthora spreads easily by droplets of contaminated water or soil (including re-used media and pots). Recent studies have found the disease can also be spread by fungus gnats and shore flies.

Monitor for this disease during the growing season when rainfall is extreme and in dry periods following heavy rainfall, as infected plants with compromised root systems will show signs of stress. Infected roots are a cinnamon color and lack white growing tips. Many of the symptoms can be confused with a nutritional disorder or over- or under- watering. To make a positive diagnosis, have a diagnostic laboratory run tests to confirm the presence of this fungal pathogen.

Phytophthora is a water mold that produces zoospores, microscopic spores that swim in standing water. Several species of Phytophthora can infect woody plants, causing a range of symptoms from cankers to root rot and foliar death. This factsheet covers Phytophthora root rot.

Monitoring

Pathogen and Disease Cycle

Introduction

Abies, Acer, Aesculus, Aucuba, Begonia, Betula, Buddleia, Buxux, Calluna, Camellia, Castanea, Cedrus, Cornus, Cotoneaster, Craetegus, Cupressocyparis leylandii, Eleagnus, Eunonymus, Forsythia, Gledistia, Ilex, Juglans, Juniper, Kalmia, Larix, Leucothoe, Ligustrum, Liquidambar, Magnolia, Malus, Nyssa, Picea, Pieris, Pinus, Platanus, Prunus, Pyrus, Quercus, Rhododendron, Salix, Syringe, Thuja, Tsuga, Ulmus, Vaccinium, Wisteria, and others.

HOST PLANTS

CULTURAL CONTROL Plant in raised beds with well drained soil. Avoid excessive irrigation. Avoid re-using containers and equipment unless they have been cleaned of organic material and soaked in disinfectant or steamed.

See sanitation guidelines in Adkins et al. (2010) below. Recycled irrigation water should also be sanitized with chlorine or other disinfestation methods before re-using.

CHEMICAL CONTROL

Please refer to http://eppserver.ag.utk.edu/redbook/sections/trees_flowers.htm for the most up to date recommendations.

Phytophthora can kill the roots (and above-ground portions) of

infected plants. Infection that destroy roots reduce the plant’s ability to

absorb water and nutrients and thus can mimic drought symptoms. A

common symptom for roots infected with Phytophthora is rapidly wilting

foliage. Other symptoms include: yellow or bronze foliage, branch

dieback, poor plant vigor and death.

Photo credits: Dr. Amy Fulcher, University of Tennessee

Adkins, C., G. Armel, M. Chappell, J.C. Chong, S. Frank, A. Fulcher, F. Hale, K. Ivors, W. Klingeman III, A. LeBude, J. Neal, A. Senesac, S. White, A. Windham. 2010. Pest Management Strategic Plan for Container and Field-Produced Nursery Crops in GA, KY, NC, SC, TN. A. Fulcher, ed. Southern Region IPM Center.

Hale, Frank, and Bruce Kauffman. "What's Happening Newletter." The Department of Entomology and Plant Pathology. Version Issue 11. N.p., 29 June 2007. Web. 29 Sept. 2011. http://eppserver.ag.utk.edu/Whats/wh2007/Issue-11-2007.pdf

University of Kentucky Publication PPFS-OR-H-09 http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-OR-H-9.pdf

Prepared by Heather Bowers, University of Tennessee Department of Plant Sciences, Intern and Dr. Amy Fulcher, University of Tennessee Assistant Professor

September 2011

Integrated Pest Management

Resources

Damage Symptoms