PP242 Charcoal Rot of Strawberries Caused by Macrophomina phaseolina1 N.A. Peres and James C. Mertely2 1. This document is PP242, one of a series of the Plant Pathology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date November 2007. Visit the EDIS Web Site at http://edis.ifas.ufl.edu. 2. N.A. Peres, assistant professor; and J.C. Mertely, coordinator research programs/services; Gulf Coast Research and Education Center--Wimauma, FL; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611. The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication does not signify our approval to the exclusion of other products of suitable composition. All chemicals should be used in accordance with directions on the manufacturer's label. The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean Introduction Charcoal rot, caused by Macrophomina phaseolina, is a relatively new disease in Florida. This disease was first observed in December 2001, when collapsed and dying strawberry plants from a commercial field were submitted to our diagnostic clinic. During the 2003 season, M. phaseolina was isolated from dying strawberry plants from the original field and two additional farms. Since then, a few additional samples are received in our diagnostic clinic every season. Affected plants are often found along field margins or other areas that were inadequately fumigated with methyl bromide. Charcoal rot has also been reported on strawberry in France, India, and Illinois. Causal Agent and Symptoms Symptoms caused by Macrophomina phaseolina are similar to those caused by other crown-rot pathogens such as Colletotrichum and Phytophthora species. Plants initially show signs of water stress and subsequently collapse (Fig.1). Cutting the crowns of affected plants reveals reddish-brown necrotic areas on the margins and along the woody vascular ring (Fig.2). To confirm a diagnosis, a sample must be submitted to a Diagnostic Clinic and the pathogen must be isolated from the diseased crowns and identified. Figure 1. Plant wilt symptom of charcoal rot.
Charcoal Rot of Strawberries Caused by Macrophomina phaseolina 2 Figure 2. Internal crown symptoms of charcoal rot. Disease Development and Spread Very little is known regarding this disease on strawberries. M. phaseolina is a common soilborne pathogen in many warm areas of the world and has a very broad host range. Many vegetable crops planted as second crops after strawberry such as squash, cantaloupe, and peppers, legumes and others are susceptible. Those infections may increase inoculum levels of M. phaseolina in the soil in the off season for strawberries. In general, high temperatures and low soil moisture favor infection and disease development. Control No fungicides are labeled for control of charcoal rot on strawberries. Topsin M is labeled for control of charcoal rot on other crops. Our preliminary results with Topsin M have shown that application of this product may delay onset of symptoms. Studies are currently being conducted to determine if cultivars differ in susceptibility to charcoal rot. This disease may be an emerging threat as the Florida strawberry industry makes the transition from methyl bromide to other fumigants.