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

Abstract

<jats:p>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 Niño 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 <jats:italic>Pythium</jats:italic> and <jats:italic>Phytophthora</jats:italic> species as the primary plant pathogens responsible for these diseases. The drastic increase of diagnostic samples identified as <jats:italic>Pythium</jats:italic> and <jats:italic>Phytophthora</jats:italic> 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.</jats:p>

Oomycete communities in lowland tropical forest soils vary in abundance and are composed of saprophytes and pathogens of seeds and seedlings of multiple plant species.

“…Due to their biology and production of swimming spores, plant-pathogenic oomycetes have the ability to increase their dispersal, growth and infection of otherwise healthy hosts as moisture availability increases (Jung 2009, Sturrock et al 2011). For this reason, oomycetes are commonly associated with significant disease epidemics during periods of increased precipitation (Thompson et al 2013, Campoverde et al 2017). The species assessed in this study are either able to cause disease ranging from minor root lesions to wilting and mortality on multiple tree species.…”