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Publication #PP195

New, Emerging, and Threatening Plant Diseases and Crop Biosecurity 1

Carrie Lapaire Harmon, Tim Momol, Jim Marois, and Pam Roberts2

SPDN: Regional Network for Crop Biosecurity

In 2002, the USDA-NIFA began its support of the National Plant Diagnostic Network, a national project and part of the USDA Homeland Security initiative to help protect agriculture by quickly detecting and accurately diagnosing and identifying new introductions of pathogens, insects, nematodes, and weeds.

Five land grant universities (University of California at Davis, Cornell University, University of Florida, Kansas State University, and Michigan State University) in the United States have been designated as the coordinating institutions for their Plant Diagnostic Regions for the US National Plant Diagnostic Network ( The Southern Plant Diagnostic Network (SPDN) at the University of Florida (UF) established this network with 11 other southern states and two US territories (Alabama, Arkansas, Georgia, Kentucky, Louisiana, Mississippi, North Carolina, Puerto Rico, South Carolina, Tennessee, Texas, US Virgin Islands, and Virginia -see Figure 1). This network's main objective is to promote the health and security of plants by rapidly and accurately identifying, intercepting, and providing management recommendations for newly introduced and re-emerging pests and pathogens that could threaten U.S. agriculture and natural ecosystems.

Figure 1. 

Southern Plant Diagnostic Network (SPDN)—"Educate to detect"

[Click thumbnail to enlarge.]

New plant diseases caused by fungal, bacterial and viral pathogens have appeared at an alarming rate in Florida in the last two decades (C. L. Harmon, P. F. Harmon, and M. T. Momol. 2006. "Florida: A Sentinel State for New and Emerging Plant Pathogens". Phytopathology 96: 546). Geographically, the state of Florida is uniquely at risk for the introduction of new pathogens and pests of plants and animals, and the climate is highly conducive to maintaining disease-inducing organisms year-round. Due to its location, heavy visitor traffic, and climate, Florida has experienced at least 4–5 new plant diseases per year. The eradication efforts of FDACS, in collaboration with scientists from UF/IFAS and USDA, have been aimed at limiting and recovering from serious disease and pest introductions.

In light of national concerns for crop biosecurity, new, emerging, and threatening plant diseases have received more attention from all interested parties. UF/IFAS Plant Disease Clinics and plant pathologists in Florida actively assist the agricultural industry in Florida and the United States by rapid and accurate detection, diagnosis, and development of management recommendations for these new diseases.

Lists of new and emerging diseases in Florida (Table 1) and elsewhere have been developed. See these websites:

NCSU site:

Damsteegt (1999) APS site:

Crop Biosecurity

Literature on crop biosecurity and biological warfare (BW) related to plant pathogens is limited. An APSnet feature article by Schaad et al. (1999) summarized the subject and presented references. For further information please visit

Plant pathologists and personnel in plant disease clinics, UF/IFAS Extension offices, and the private sector are the first line of defense against new diseases (Miller, S., F. Beed, and C. L. Harmon 2009. "Plant Disease Diagnostic Capabilities and Networks". Annual Review of Phytopathology). In the state of Florida, the four official plant disease clinics, many plant pathologists at several RECs, and 67 County Extension offices are networked against a potential threat from introduced plant pathogens. The Florida Plant Diagnostic Network (FPDN,, UF/IFAS's web-based Distance Diagnostic and Identification System (DDIS,, and the National Plant Diagnostic Network (NPDN, are playing an important role in the accomplishment of this goal. Improvement in the infrastructure of plant disease clinics and in the DDIS capabilities of County Extension offices is essential for defense against new diseases.

Scientists at UF/IFAS, USDA, and FDACS are providing research support for discoveries, rapid detection, identification, and mitigation of plant pathogens. For a more secure future of Florida's crops and food supply, research needs further enhancement in epidemiology, molecular biology, and in all disciplines of plant pathology. This investment is needed to maintain the competitiveness of Florida's agricultural sector. Specific areas that need further research are the following:

  • Improvements in basic identification of and discrimination between new pathogens

  • Molecular and immunological detection methods, PCR, real time PCR, and molecular fingerprinting techniques

  • Epidemiology and management of new and exotic plant diseases

  • Development of disease resistant genotypes through classical breeding and genetic engineering

  • Enhanced distance diagnostics, training, and communications regarding new and high-impact diseases

County Extension Faculty (First Detector Educators) and First Detectors

Our educators and First Detectors are our first line of defense against new, emerging, or other high-impact plant diseases. If you encounter an unfamiliar disease symptom on any plant, immediately take digital images of the symptoms and send them to multiple plant pathology specialists through DDIS. You may also send samples to the closest plant disease clinic or plant pathologist. Diagnostic fees may not be charged for samples associated with crop biosecurity and high-impact diseases in Florida; call your diagnostic clinic or extension office before sending the sample to confirm this. Prepare newsletter and media articles on the subject of emerging and high-impact diseases to increase awareness among your clientele and Florida citizens. For further information, or in an emergency situation, contact one of the plant disease diagnostic laboratories and offices listed below.


UF/IFAS Florida Extension Plant Diagnostic Center
University of Florida
Bldg. 1291, 2570 Hull Rd.
PO Box 110830
Gainesville, FL 32611-0830 
Phone: 352-392-1795 
FAX: 352-392-3438

Note: For overnight mail or package delivery service (UPS, Fedex, etc.) be sure to include the physical street address: “UF, Bldg. 1291, 2570 Hull Rd.”


Florida Extension Plant Diagnostic Clinic–Quincy
UF/IFAS North Florida Research and Education Center
155 Research Road
Quincy, FL 32351
Phone: 850-875-7140
FAX: 850-875-7148


Florida Extension Plant Disease Clinic–Homestead
UF/IFAS Tropical Research and Education Center
18905 SW 280th St.
Homestead, FL 33031-3314
Phone: 305-246-6340
FAX: 305-246-7003


Florida Extension Plant Disease Clinic–Wimauma
UF/IFAS Gulf Coast Research and Education Center
14625 CR 672
Wimauma, FL 33598
Phone: 813-634-0000
FAX: 813-634-0001

Southern Plant Diagnostic Network

UF/IFAS Plant Pathology
1453 Fifield Hall
PO Box 110680
Gainesville, FL 32611-0680
Phone: 352-273-4645
FAX: 352-392-7348

American Phytopathological Society listing of university diagnostic laboratories:


Table 1. 

List of important new and emerging diseases in Florida. This is a dynamic list and subject to change.



Major Hosts

Internet Source

Rose rosette

Rose rosette virus

Rosa spp.

Basil downy mildew

Peronospora belbahrii

Basil, Coleus, Salvia

Gladiolus rust

Uromyces transversalis

Gladiolus, Crocosmia

Bacterial fruit blotch

Acidovorax avenae subsp. citrulli


Citrus canker

Xanthomonas axonopodis pv. citri

Citrus spp.

Daylily rust

Puccinia hemerocallidis


Tomato Yellow Leaf Curl (TYLC)

TYLCV (new strains or New Begomoviruses)

Tomato ornamentals

Tomato spotted wilt (TSW)

TSWV (new strains) New Tospoviruses

Tomato, peanut, tobacco, potato, pepper

Impatiens necrotic spot (INS)



Bacterial wilt

Ralstonia solanacearum especially race 3

Tomato, potato,tobacco,



Karnal bunt

Tilletia indica


Chrysanthemum white rust

Puccinia horiana


Citrus variegation

Citrus variegated chlorosis ilarvirus (CVC)




Ca. Liberibacter asiaticus


Pierce's disease and bacterial scorch

Xylella fastidiosa

Grape, blueberry, ornamentals, and more

Potato cyst nematode

Globodera pallida

Potato family, (including tomato, eggplant, and some weeds)

Plum pox

Plum pox virus (PPV)

Stone fruits

Potato mop-top

Potato mop-top virus (PMTV)


Soybean rust

Phakopsora spp.




This document is PP195, one of a series of the Plant Pathology Department, UF/IFAS Extension. Original publication date December 2002. Revised August 2010 and January 2014. Visit the EDIS website at


Carrie Harmon, Associate In, Plant Pathology Department; Tim Momol, extension director, Central region; Jim Marois, professor, Plant Pathology Department, North Florida Research and Education Center, Quincy; Pam D. Roberts, associate professor, Southwest Florida Research and Education Center (SWREC), Immokalee; UF/IFAS Extension, Gainesville, FL 32611.

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. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.