Speakers: Dr. Bikash Ghimire, Assistant Professor and Extension Specialist in Ornamental Plant Pathology, UGA Athens Campus; Dr. Shimat Joseph, Associate Professor of Entomology, UGA Griffin Campus
Webinar Date: November 13, 2025
Moderator: Rich Braman, UGA Center for Urban Agriculture
Duration: 53:00
NARRATIVE SUMMARY
This comprehensive ornamentals industry update webinar introduced Dr. Bikash Ghimire to the Georgia Green Industry and featured Dr. Shimat Joseph addressing emerging insect pest challenges. Dr. Ghimire, who joined UGA in August 2025 as the new ornamental plant pathology extension specialist replacing Dr. Jean Williams-Woodward, presented his educational background and outlined his extension-focused program vision. After completing his bachelor’s degree in Nepal, Dr. Ghimire earned his master’s degree from Washington State University in crop science and his PhD from the University of Georgia, followed by three years as a postdoctoral researcher at the Griffin campus. His presentation emphasized the fundamental disease triangle concept and provided historical context with examples including chestnut blight caused by Cryphonectria parasitica and sudden oak death caused by Phytophthora ramorum, illustrating how devastating new pathogens can reshape entire ecosystems.
Dr. Ghimire identified three major disease categories affecting Georgia’s ornamental horticulture industry, which ranks as the state’s fourth largest commodity group with over one billion dollars in farm gate value and nearly 67,000 people employed. Root and crown diseases caused by oomycetes including Pythium and Phytophthora, along with fungi such as Rhizoctonia and Thielaviopsis, represent the most significant challenge in greenhouse and nursery operations. Based on samples received at the UGA Plant Disease Clinic in Athens during 2025, Thielaviopsis and Phytophthora were the predominant root and crown rot pathogens observed. Dr. Ghimire emphasized the critical importance of accurate pathogen diagnosis because fungicides effective against oomycetes, such as mefenoxam and metalaxyl, have limited efficacy against true fungi, while fungicides like thiophanate-methyl and azoxystrobin work well for fungal pathogens but not oomycetes. He demonstrated the Agdia immunostrip test, a rapid field diagnostic tool that provides results within five minutes for Phytophthora detection, enabling growers to make informed treatment decisions quickly.
Foliar diseases including leaf spots caused by Cercospora, Alternaria, Entomosporium, and Colletotrichum constitute the second major category, while viral diseases transmitted by aphids represent the third. Dr. Ghimire highlighted two emerging disease threats requiring immediate attention. Vascular streak dieback, caused by Ceratocystis species, affects more than 34 woody ornamental species including red maple, dogwood, and redbud, causing wilting, leaf scorching, yellowing, and vascular discoloration. First reported in Tennessee and North Carolina in 2019, the disease has now been documented in 11 states, with one Virginia nursery losing 90 to 100 percent of their dogwood rootstock in 2022. Although Georgia remains officially unreported, Dr. Ghimire suspects the pathogen is already present based on conversations with nursery professionals. Lethal bronzing disease, affecting sabal palms in Thomasville near the Florida state line, was confirmed in Georgia for the first time in 2024 when samples sent to Florida tested positive. This phytoplasma disease progresses from oldest leaves upward, creating bronze-like browning and eventually killing infected palms.
Boxwood diseases received particular attention, with Dr. Ghimire discussing boxwood blight caused by Calonectria, boxwood dieback, and volutella blight. Korean boxwood cultivars demonstrate greater resistance to blight compared to other varieties. His research priorities include screening cultivars for disease resistance at the UGA Mountain Research Station in Blairsville, evaluating chemical and biological fungicides for efficacy, and developing integrated disease management strategies combining host resistance, cultural practices, and targeted chemical applications. Dr. Ghimire emphasized his 85 percent extension role, expressing commitment to site visits, stakeholder engagement, county agent collaboration, and disseminating science-based recommendations through traditional extension publications and digital platforms including webinars and conferences. He encouraged industry professionals to complete his survey on major disease challenges to help shape his research program for years to come.
Dr. Shimat Joseph’s entomology presentation focused on the two-spotted cotton leafhopper (Austroasca viridigrisea), an invasive pest that emerged as a significant threat to Georgia ornamentals and agriculture in 2025. Native to a geographic range spanning Africa to Japan, this leafhopper was first detected in the United States in Puerto Rico and the U.S. Virgin Islands in 2013, reached Florida in 2023, and spread to five states including Georgia by 2025. The pest poses a serious problem in cotton production, with growers struggling to manage populations despite intensive insecticide applications. Dr. Joseph explained that the pest likely spreads through storm systems moving from Florida’s east coast northward and through movement of infested plant material. The leafhopper attacks 27 known plant species, primarily within the Malvaceae and Solanaceae families, with cotton, okra, and multiple hibiscus species serving as confirmed reproductive hosts where complete generations can develop.
On ornamental hibiscus, Dr. Joseph documented infestations on tropical hibiscus (Hibiscus rosa-sinensis), rose of Sharon (H. syriacus), and UGA-developed hybrids bred by Dr. Jan Ruter. The pest causes yellowing, browning, leaf curling, and necrosis, with affected leaf portions turning brown before dropping. Field observations revealed differential susceptibility within plant families, with eggplants and okra experiencing severe damage while tomatoes and peppers in the same Solanaceae family showed minimal impact. Adults measure 2 to 3 millimeters in length and display distinctive two dark spots, characteristics that distinguish them from similarly-sized potato leafhoppers which lack these markings. Dr. Joseph’s research team surveyed multiple plant species, finding no leafhopper colonization on tested hosts including crepe myrtle and certain hydrangea cultivars, suggesting potential for host plant resistance. Management recommendations emphasized integrated approaches including monitoring for early detection, using action thresholds before populations explode, and strategic insecticide applications when warranted.
Dr. Joseph addressed a critical question about whitefly management on viburnum in coastal Georgia, explaining that whiteflies migrate from cotton fields after harvest, creating severe pressure on ornamental nurseries and residential landscapes. He recommended imidacloprid (Dominion) applied as a soil drench for long-term systemic control lasting up to two months, particularly valuable when planned proactively. For immediate knockdown, contact insecticides such as bifenthrin (a pyrethroid) provide rapid results but require repeat applications as residues degrade and new populations migrate in from surrounding areas. The presentation concluded with discussion of resistance management strategies, emphasizing rotation between insecticide classes to preserve product efficacy and prevent resistance development in pest populations.
YOUTUBE TIMESTAMPS
0:00 Introduction and Overview
0:33 Dr. Bikash Ghimire Introduction and Background
1:50 Educational Journey: Nepal to Washington State to UGA
2:35 Joining UGA as Ornamental Pathology Extension Specialist
2:54 Presentation Outline: Plant Pathology and Industry Overview
3:08 Disease Triangle and Major Pathogen Categories
3:48 Historical Context: Chestnut Blight
5:00 Sudden Oak Death: Phytophthora ramorum Case Study
5:52 Georgia’s Ornamental Horticulture Industry Overview
6:48 Major Disease Categories Affecting Georgia Ornamentals
7:36 Root and Crown Diseases: Oomycetes and Fungi
9:24 Foliar Diseases and Viral Pathogens
10:17 Extension and Applied Research Program Vision
12:06 UGA Plant Disease Clinic Overview and Services
13:06 Survey and Surveillance of Existing Diseases
13:38 Root and Crown Rot: Thielaviopsis and Phytophthora
14:40 Fungicide Selection: Matching Chemistry to Pathogen Type
14:57 Rapid Field Diagnostics: Immunostrip Test Demonstration
15:23 Emerging Disease Threats in Georgia
15:40 Vascular Streak Dieback: Ceratocystis Species
17:20 Management Options for Vascular Streak Dieback
17:55 Lethal Bronzing Disease: First Georgia Detection
19:11 Boxwood Diseases: Blight, Dieback, and Volutella
20:32 Boxwood Blight Symptoms and Diagnosis
21:47 Boxwood Disease Management Strategies
22:55 Cultivar Screening Research at Blairsville
24:03 Future Research Priorities and Industry Survey
24:45 Q&A: Boxwood Blight Management and Soil Treatment
27:01 Transition to Entomology Presentation
28:00 Dr. Shimat Joseph Introduction
28:19 Whitefly Management on Viburnum Q&A
29:20 Systemic vs. Contact Insecticide Strategies
31:00 Turfgrass and Ornamental Pest Management Website
32:08 Emerging Pest Alert System and Resources
33:01 Two-Spotted Cotton Leafhopper Introduction
33:25 Native Range and U.S. Introduction Timeline
34:20 Host Range: Hibiscus Species Confirmation
35:01 Literature Review: 27 Known Host Plant Species
35:52 Malvaceae and Solanaceae as Primary Host Families
36:48 Reproductive Hosts vs. Incidental Hosts
37:13 Damage Symptoms: Yellowing, Browning, and Necrosis
37:30 Okra Field Damage Observations
38:22 Hibiscus Symptoms and Population Levels
39:22 Adult Morphology and Identification Features
40:18 Distinguishing from Potato Leafhopper
41:22 Host Susceptibility Research Findings
42:48 Differential Damage Within Plant Families
43:38 Survey Results: Non-Host Plant Species
44:43 Management Approach and Action Thresholds
45:38 Insecticide Efficacy and Application Timing
46:48 Systemic Insecticides: Neonicotinoids and Alternatives
48:08 Contact Insecticides: Pyrethroids and Application Strategy
49:30 Resistance Management and Product Rotation
50:48 Summary and Key Takeaways
52:35 Final Q&A and Webinar Conclusion
53:00 Closing Remarks and CEU Sign-In Instructions
QUESTIONS & ANSWERS
Q: What are the most common root and crown rot pathogens affecting Georgia nurseries in 2025?
A: Based on samples processed through the UGA Plant Disease Clinic in Athens during 2025, the majority of root and crown rot diseases were caused by either Thielaviopsis or Phytophthora. These two pathogens represent the most significant threats to greenhouse and nursery operations in Georgia, requiring accurate diagnosis to ensure appropriate fungicide selection.
Q: Why is it important to distinguish between fungal and oomycete pathogens before applying fungicides?
A: Fungicides effective against oomycetes such as mefenoxam and metalaxyl have limited efficacy against true fungi, while fungicides like phosphonates, thiophanate-methyl, and azoxystrobin work well for fungal diseases but not oomycetes. Without accurate diagnosis, growers may apply ineffective products, wasting resources and allowing disease to progress unchecked. Rapid diagnostic tools like immunostrip tests can provide Phytophthora identification in as little as five minutes.
Q: What is vascular streak dieback and should Georgia growers be concerned?
A: Vascular streak dieback is caused by Ceratocystis species fungi and affects more than 34 woody ornamental species including red maple, dogwood, and redbud. First reported in Tennessee and North Carolina in 2019, the disease has spread to 11 states, with one Virginia nursery losing 90 to 100 percent of their dogwood rootstock in 2022. Although Georgia has not been officially reported, conversations with nursery professionals suggest the pathogen may already be present in the state, making vigilance and early detection critical.
Q: What is lethal bronzing disease and where was it detected in Georgia?
A: Lethal bronzing disease is caused by a phytoplasma that affects sabal palms. In August 2024, samples from Thomasville, Georgia, near the Florida state line, were sent to Florida for testing and confirmed positive for lethal bronzing. The disease progresses from the oldest leaves upward, causing bronze-like browning of the foliage and eventually killing the palm. This represents the first confirmed detection of lethal bronzing disease in Georgia.
Q: Which boxwood cultivars show the best resistance to boxwood blight?
A: Korean boxwood cultivars demonstrate greater resistance to boxwood blight compared to other varieties. Dr. Ghimire is conducting cultivar screening research at the UGA Mountain Research Station in Blairsville to identify commercially available cultivars and breeding lines with improved disease resistance for long-term use in Georgia landscapes.
Q: If you have a hedge of boxwoods with blight, should you remove all plants and treat the soil before replanting?
A: The decision depends on several factors including plant age, the severity of infection, and your attachment to the existing plants. If infection is severe and widespread, replacement may be the most practical option. However, if the infection is moderate, proper pruning for one year may allow recovery, though it will take time to restore the aesthetic appearance. There is evidence that boxwoods can recover with appropriate pruning, but patience is required as recovery takes longer than one to two years.
Q: What is the two-spotted cotton leafhopper and why is it a concern for Georgia?
A: The two-spotted cotton leafhopper (Austroasca viridigrisea) is an invasive pest native to Africa through Japan that was first detected in Puerto Rico in 2013, reached Florida in 2023, and spread to five states including Georgia in 2024. It causes serious damage to cotton and multiple ornamental species, particularly hibiscus, okra, and eggplant. Adults are 2 to 3 millimeters long with two distinctive dark spots, and they cause yellowing, browning, leaf curling, and necrosis on host plants.
Q: Which hibiscus species are affected by the two-spotted cotton leafhopper?
A: The leafhopper has been confirmed on multiple hibiscus species including tropical hibiscus (Hibiscus rosa-sinensis), rose of Sharon (Hibiscus syriacus), and UGA-developed hybrids. These serve as reproductive hosts where the pest can complete full generations, laying eggs and developing from nymph to adult on the same plant.
Q: How can you distinguish the two-spotted cotton leafhopper from other small leafhoppers?
A: The two-spotted cotton leafhopper measures 2 to 3 millimeters in length and has two distinctive dark spots on its body. Potato leafhoppers are similar in size but lack these characteristic spots. Additionally, the two-spotted cotton leafhopper’s host range and damage symptoms help confirm identification, particularly when found on hibiscus, cotton, or okra.
Q: Do all plants in the Solanaceae family show equal susceptibility to the two-spotted cotton leafhopper?
A: No, there is significant variability in susceptibility within the same plant family. Field observations showed that eggplants and okra experience severe damage and high leafhopper populations, while tomatoes and peppers in the same Solanaceae family showed minimal to no damage. This differential susceptibility suggests complex host-pest interactions that may be exploited for resistance-based management.
Q: What is the best management approach for whiteflies on viburnum in coastal Georgia?
A: For whitefly management, imidacloprid (Dominion) applied as a soil drench provides systemic control lasting up to two months and works best when applied proactively before population explosions occur. For immediate knockdown of existing populations, contact insecticides such as bifenthrin (a pyrethroid) provide rapid control but require repeat applications every 14 days as residues degrade and new whiteflies migrate in from surrounding properties, particularly after cotton harvest.
Q: How should growers manage insecticide resistance in leafhopper and whitefly populations?
A: Resistance management requires rotating between different insecticide classes rather than repeatedly using the same product or mode of action. Professional applicators with access to multiple product classes should alternate between chemical groups to avoid selection pressure. Homeowner products are more limited, but alternating between available formulations containing different active ingredients helps preserve efficacy. Avoid continuous use of any single product or chemical class throughout the growing season.
ADDITIONAL RESOURCES
Dr. Bikash Ghimire Contact:
Email: bikash.ghimire@uga.edu
Extension: Ornamental Plant Pathology
Dr. Shimat Joseph Contact:
Email: shjo@uga.edu
Lab Website: Turfgrass and Ornamental Pest Management
UGA Griffin Campus
Sign up for pest alerts and blog updates
UGA Plant Disease Clinic:
Location: Athens, Georgia
Services: Free diagnostic services for commercial clientele
Process: Submit samples through county extension agents with clinic submission form
Diagnosis includes pathogen identification and management recommendations
Industry Survey:
Dr. Ghimire’s Ornamental Disease Survey – Available through UGA Extension
Purpose: Identify major disease challenges facing Georgia’s ornamental industry
Pest Resources:
Turfgrass and Ornamental Pest Management Website (Dr. Joseph’s lab)
- Blog articles on emerging pests
- Email alerts for new pest detections
- Pest identification guides
- Biology and management information
Key Topics for Future Research:
- Boxwood cultivar screening for disease resistance
- Fungicide and biofungicide efficacy trials
- Vascular streak dieback surveillance and management
- Lethal bronzing disease monitoring
- Two-spotted cotton leafhopper host range and control
- Integrated pest management for ornamental landscapes
For questions about ornamental plant diseases, contact Dr. Bikash Ghimire. For questions about insect pests on ornamentals and turfgrass, contact Dr. Shimat Joseph.
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