Fungal Diseases of Plants

Monica L. Elliott
Other Contacts: Braham Dhillon

Graphiola leaf spot, also referred to as "false smut," is a foliar pathogen of certain palm species. In Florida, it is primarily a cosmetic disease and does not adversely affect plant growth. Nutrient deficiencies, such as potassium or magnesium deficiency, are much more serious palm health problems than this disease, especially for Phoenix species.

Stephen H. Futch andL. W. Timmer

Greasy spot is a disease that's frequently found in tropical and semitropical regions where citrus cultivars are grown. The disease is caused by Mycosphaerella citri. Symptoms appear as yellow to dark brown to black lesions occurring first on the underside of mature citrus leaves (Fig. 1). As the lesions develop on the underside of the leaves, they become darker and a corresponding chlorotic spot will appear on the upper leaf surface. These yellow (chlorotic) spots occur when infected cells fail to develop chlorophyll. Lesions are more yellowish and diffuse on lemons and grapefruit and more raised and darker on tangerines. Affected leaves fall prematurely from the tree during the fall and winter resulting in reduced tree vigor and yield. Greasy spot also infects the fruit of grapefruit trees producing rind blotch.

Daniel Mancero-Castillo, Ali Sarkhosh, Sara Sherman, Mercy Olmstead, Philip Harmon, and Thomas Beckman

Daniel Mancero-Castillo, Ali Sarkhosh, Courtney Ligon, Mercy Olmstead, and Philip Harmon

Monica L. Elliott
Other Contacts: Braham Dhillon

Monica L. Elliott
Other Contacts: Braham Dhillon

Juliana Baggio, Juliana S. Baggio, J. C. Mertely, J. C. Mertely, andNatalia A. Peres

Several different fungi and one bacterium cause leaf spot diseases of strawberry. Symptoms caused by these pathogens are often similar, leading to confusion and misdiagnosis of the disease. This publication focuses on helping growers, crop consultants, and Extension agents with the diagnosis and identification of the most common strawberry leaf spot diseases found in Florida.

Monica L. Elliott andPhilip F. Harmon

Yin-Tse Huang, Jeffrey Eickwort, Jeffrey M. Eickwort, andJiri Hulcr

All pine species in Florida are susceptible to red heart disease. The disease can decrease timber value and weaken trees, making them threats to people and property. In forests, however, the same disease can be beneficial to cavity-nesting animals like red-cockaded woodpeckers. This fact sheet describes the disease and provides some tips to manage it in areas where it could cause problems for people.

Yin-Tse Huang and Jiri Hulcr

Mathews L. Paret, Nicholas S. Dufault, Mason Newark, and Joshua H. Freeman

Gummy stem blight (GSB) is a major disease of many cucurbits, including watermelon, cantaloupe, cucumber, pumpkin, squash, muskmelon, and other melons. The disease is also known as black rot due to its characteristic appearance on infected fruits. Learn the symptoms, causal agent and disease spread, and fungicides labeled for use in Florida.

Jozer Mangandi andNatalia A. Peres

The article describes this fungal disease that that affects nearly all rose cultivars worldwide — causal agent and geographic distribution, symptoms, and control.

Monica L. Elliott
Other Contacts: Braham Dhillon

This fact sheet is limited to those diseases where the pathogens only infect (invade) and cause spots and blights of the leaf blade. Other diseases may cause death of leaflets and leaf segments but are actually the result of a pathogen infecting the leaf petiole or rachis.

Qingren Wang, Shouan Zhang, and Teresa Olczyk

Powdery mildew is one of the most commonly occurring diseases on many types of beans. Although the causal organism rarely causes extensive damage, significant yield losses were reported in Columbia County when infection occurred in dry beans prior to flowering. Accurately identifying this disease and immediately taking action for control are critical to effectively prevent spread of powdery mildew in order to reduce significant losses of yield and quality.

Norma C. Flor, Douglas A. Phillips, andPhilip F. Harmon

Stem blight is the most common disease that kills our blueberry bushes in Florida. In most cases, stem blight finishes the job, but other stresses play a lead or contributory role. When stem blight starts showing up in a production field, first check for all of the above discussed stressors, diseases, and pests. Once identified, developing an integrated and comprehensive disease management plan will help you stay one step ahead of stem blight.

Monica L. Elliott
Other Contacts: Braham Dhillon

Thielaviopsis paradoxa is a fungus that can infect any part of a palm and so can cause numerous diseases. In Florida, the two most frequent (and usually lethal) Thielaviopsis diseases observed in the landscape and field nursery are a bud (heart) rot and trunk rot.

Katy Deitz, Alassane Sow, Claudia A. Paez, Jeffrey Eickwort, Michelle A. Jusino, andMatthew E. Smith

Starting in 2019 in northern and central Florida, a thread blight caused by a previously undescribed fungus was observed with increasing frequency, affecting both hardwood and conifer hosts with a higher prevalence in wet, shaded environments. This emerging disease, called relampago blight, is caused by the fungus Parvodontia relampaga and is characterized by its distinct white, lightning-shaped rhizomorphs (fungal cords) that grow on the stems and branches of affected host plants. When the fungus fully develops, it can also grow on the undersides of plant leaves, causing dieback of leaves and small branches. This fungus has been found on a wide array of host plants and detected in 31 counties throughout Florida.

Juliana Baggio, Juliana S. Baggio, andNatalia A. Peres

A UF/IFAS numbered peer reviewed Fact Sheet for Commercial audience(s). Published by Integrated Pest Management

Nalleli Garcia, Rachel Kalicharan, and Jessie Fernandez Garcia

The purpose of this document is to increase awareness of rice blast disease by describing its lifestyle, symptoms, and current disease mitigation practices. Given that the Everglades Agricultural Area (EAA) plays a vital role in rice cultivation, this publication is also intended for Florida rice growers to be used as a diagnostic field guide in the identification and management of rice blast disease. Written by Nalleli Garcia, Rachel Kalicharan, and Jessie Fernandez Garcia, and published by the UF/IFAS Department of Microbiology and Cell Science, September 2024.

C. Benton Willis, Michael Goodnight, Jessica Velte, Marin T. Brewer, andMatthew E. Smith

Exobasidium fungi are plant pathogens that primarily infect plants in the Ericaceae family, including blueberries and azaleas. Their infections cause plant cells to proliferate (hyperplasia) and expand (hypertrophy). The fungi then use the increased surface area to produce spores. These changes manifest as symptoms on the host plant, varying by species of Exobasidium. The range of symptoms includes leaf and fruit spots, blisters, shoot proliferation (witches' broom), and galls. Infected plant tissues can also become swollen and distorted, as well as chlorotic (yellow) or discolored (reddish to pink). As this infected tissue matures, the surface becomes white and powdery from fungal spore production. Exobasidium fungi tend to cause symptoms on the plant during ideal weather conditions but can likely survive on the leaf surface or other available substrates year-round. Disease management includes chemical applications and cultural practices before the spores have the chance to mature.

Hui-Ling Liao, Haihua Wang, Kaile Zhang, Benjamin Reimer, Brittany Justesen, Joseph Walter, Joseph H. Walter, Robert (Robbie) Jones, Vijay Verma, Ann Blount, andCheryl Mackowiak

Rust is a common disease on warm-season grasses that can affect pasture health and potentially serve as an allergen for animals grazing on it. Despite its significance, rust disease in warm-season grass is often overlooked. This publication reports on rust disease observed in Florida pastures and offers practical, non-technical knowledge and general management suggestions to mitigate the threat of rust disease. It is aimed at producers, landowners, and the public.

Philip F. Harmon

A UF/IFAS numbered Fact Sheet.

Megan M. Dewdney

2026–2029 Florida Citrus Production Guide (Citrus Production Fundamentals).

Ali Sarkhosh, Shirin Shahkoomahally, Logan Marie Richmond-Cosie, andPhilip F. Harmon

Brown rot disease can occur on all stone fruit cultivars grown in Florida, including peaches, nectarines, and plums. Early-maturing varieties and natives can serve as sources of inoculum for later-maturing fruit cultivars.

Jennifer L. Gillett-Kaufman, Sandra A. Allan, Jonael H. Bosques-Mendez, and Lyle J. Buss

A UF/IFAS numbered Management for Commercial audience(s). Published by Integrated Pest Management

Megan M. Dewdney

2026–2027 Florida Citrus Production Guide (Current Season Spray Guide).

Philip F. Harmon

[ABSTRACT]

Philip F. Harmon, Carrie L. Harmon, Aaron J. Palmateer, andStephen H. Brown

A UF/IFAS numbered Fact Sheet.

Shawn Steed, Wael Elwakil, Marissa Cassaway, andGary Vallad

Viburnum sp. is an important woody ornamental crop for nursery growers in Florida. Around 2014, growers indicated that common labeled fungicides targeting downy mildew failed to provide acceptable levels of disease management. Through a research grant from the Florida Nursery, Growers and Landscape Association, UF/IFAS researchers and UF/IFAS Extension Hillsborough County agents conducted studies to determine fungicide efficacy of oomycete fungicides to help nursery professionals produce and maintain a healthy viburnum crop. Written by Shawn Steed, Wael Elwakil, Marissa Cassaway, and Gary Vallad, and published by the UF/IFAS Department of Environmental Horticulture, December 2025.

Pamela D. Roberts, Mathews Paret, and Nicholas Dufault

This document discusses the symptoms and management of powdery mildew, a problematic fungal disease, on watermelon in Florida.

Philip F. Harmon, Christ Mane Belizaire, andDouglas A. Phillips

Leaf rust is an important disease of southern highbush blueberries (SHB) in Florida and can be particularly costly in the evergreen production system. Severe leaf rust causes defoliation in the fall or early winter, which can decrease floral bud differentiation, photosynthesis, and the next season’s fruit yield. Florida blueberry growers consistently list leaf rust among their top-three disease concerns in UF/IFAS surveys. This publication will present information for Florida blueberry growers on the disease cycle, symptoms, and integrated management of this fungal leaf disease.