A High Incidence of Pythium and Phytophthora Diseases Related to Record-breaking Rainfall in South Florida

Abstract

Florida’s ornamental plant industry flourishes due to environmental conditions that allow for a 12-month growing season. Florida leads the nation in production of tropical foliage, and Miami-Dade County ranks number one in nursery and landscape production with sales reaching $2 billion annually. The well-advertised El Nin ̃o pattern made its presence felt this past winter in south Florida with the wettest conditions since record keeping began in 1932. As a result, ornamental nursery growers contended with a higher incidence of root rots, crown rots, and foliar blight diseases, confirmed by samples submitted to the University of Florida’s Extension Plant Diagnostic Clinic in Homestead, FL. The present study focused on environmental conditions occurring over the past 4 years and included rainfall, solar radiation, and temperature variables and examined their influence on the incidence of diseases affecting ornamental plants. Results indicated Pythium and Phytophthora species as the primary plant pathogens responsible for these diseases. The drastic increase of diagnostic samples identified as Pythium and Phytophthora can be attributed to the unusually wet weather experienced. These two oomycetes are well known for causing disease under wet conditions and growers should closely monitor weather forecasts and practice preventative disease management accordingly.