Speaker: Dr. Ruchika Kashyap, Assistant Professor and Extension Specialist of Urban and Controlled Environment Plant Pathology, University of Georgia Athens Campus
Webinar Date: March 13, 2025
Moderator: Dr. Bodie Pennisi, UGA Extension Horticulturist
Duration: 49:52
NARRATIVE SUMMARY
Dr. Ruchika Kashyap, a newly hired assistant professor and extension specialist at the University of Georgia’s Department of Plant Pathology, delivered a comprehensive educational webinar introducing fundamental plant disease concepts and their application to emerging urban and controlled environment agriculture systems. Her presentation bridged traditional plant pathology principles with the unique challenges facing Georgia’s growing indoor agriculture industry, providing practical diagnostic and management guidance for pest management professionals.
The webinar opened with essential plant disease fundamentals, beginning with the critical distinction between symptoms (what we observe on plants) and signs (visible pathogen presence). Dr. Kashyap emphasized a detective-like diagnostic approach, encouraging growers to ask comprehensive questions about plant care history, symptom patterns, timing, and environmental conditions. She explained that successful disease diagnosis requires understanding whether problems stem from biotic causes (fungi, bacteria, viruses, nematodes, oomycetes) or abiotic factors (pollution, herbicide drift, nutrient imbalances, temperature extremes, water stress). The classic disease triangle—requiring a susceptible host, virulent pathogen, and favorable environment—served as the foundation for understanding disease prevention strategies.
Dr. Kashyap provided detailed coverage of major pathogen groups, beginning with fungi as the most important plant disease agents, including over 8,000 pathogenic species. She demonstrated how plant pathologists use microscopic characteristics to identify pathogens, including hyphal structures in Rhizoctonia (diagnostic 90-degree branching patterns), fruiting bodies like cleistothecia in powdery mildew fungi, and distinctive spores such as the banana-shaped multicellular conidia of Fusarium. Bacterial pathogens, though lacking the spore structures of fungi, produce characteristic symptoms including tissue disintegration, water-soaking, and bacterial ooze, spreading primarily through water splash, tools, and insects. Viral diseases, visible only through electron microscopy, cause systemic symptoms like mosaics, mottling, and stunting, transmitted by insect vectors and mechanical means. Nematodes, microscopic roundworms residing in soil, cause distinctive root galling and damage visible to careful observers. Abiotic disorders including cold injury, heat stress, and herbicide damage produce characteristic uniform patterns across multiple host species, distinguishing them from the random distribution typical of infectious diseases.
Transitioning to urban and controlled environment agriculture (CEA), Dr. Kashyap highlighted the growing importance of these systems for year-round food production in Georgia. She introduced UGA’s new CEA research team comprising five specialists covering crop physiology, plant pathology, phenomics, breeding, and entomology, with infrastructure development underway at both Athens and Griffin campuses. Georgia’s CEA systems range from low-tech hoop houses and high tunnels to sophisticated hydroponic, aeroponic, and aquaponic facilities, growing primarily tomatoes, lettuce, cucumbers, peppers, and strawberries. These controlled environments present unique disease challenges despite environmental regulation.
Common CEA diseases discussed included Botrytis (gray mold), which thrives on injured tissue under high humidity and requires dry canopy management and proper ventilation. Powdery mildew produces superficial fungal growth beginning with chlorotic spots, paradoxically controlled by direct water application since the pathogen avoids free moisture. Black leg disease caused by Plectosphaerella affects basil crops, representing an emerging concern in Georgia’s herb production facilities. Root diseases dominated by oomycete pathogens like Pythium and Thielaviopsis pose the most significant challenges in hydroponic systems where water-loving pathogens thrive. Dr. Kashyap emphasized that different Pythium species prefer different temperature ranges, making species-level diagnosis critical for effective water temperature management strategies.
The presentation concluded with systematic disease management recommendations prioritizing prevention through sanitation, exclusion, and environmental manipulation. Dr. Kashyap stressed that chemical fungicides should serve as the last resort, particularly in indoor production where label restrictions often prohibit conventional pesticide use. She advocated for integrated approaches including resistant varieties, proper spacing, optimized air circulation, humidity control, tool sterilization, and careful monitoring of pathogen entry points through seeds, growing media, water, and human traffic. The webinar concluded with audience questions addressing the practical challenges facing Georgia’s controlled environment growers.
YOUTUBE TIMESTAMPS
0:00 Introduction and Welcome
1:17 Dr. Kashyap Introduction and Background
1:44 Webinar Overview: Plant Diseases in Urban and Controlled Environments
2:28 Plant Disease Basics: What is a Plant Disease?
3:05 Disease Symptoms: Belowground, Aboveground, and Systemic
4:22 Diagnostic Approach: Asking the Right Questions
6:05 Distinguishing Biotic from Abiotic Disease Patterns
7:11 The Disease Triangle: Host, Pathogen, Environment
9:30 Causal Agents: Biotic Pathogens Overview
9:54 Abiotic Disease Factors: Pollution, Herbicide Drift, Nutrient Stress
10:38 Disease vs. Injury: Understanding the Difference
11:09 Fungi: The Most Important Pathogen Group
12:48 Fungal Structures: Hyphae, Mycelium, and Diagnostic Features
13:27 Rhizoctonia Identification: 90-Degree Hyphal Branching
13:54 Fungal Fruiting Bodies and Spore Production
14:57 Cleistothecia: Powdery Mildew Fruiting Bodies
15:46 Fusarium Spores: Banana-Shaped Multicellular Conidia
16:10 Thielaviopsis: Dark Pigmented Multicellular Spores
16:27 Oomycetes: Fungal-Like Water-Loving Pathogens
17:18 Pythium and Phytophthora: Soil-Borne Oomycetes
18:24 Bacterial Plant Diseases: Characteristics and Symptoms
19:14 Bacterial Cell Structure and Identification
19:48 Viral Plant Diseases: Submicroscopic Pathogens
21:04 Nematodes: Microscopic Roundworm Pathogens
23:06 Abiotic Disorders: Environmental and Cultural Factors
25:05 Cold Injury Examples on Woody Plants
25:47 Heat Injury on Rhododendron
26:01 Abiotic Damage Patterns: Uniform Distribution
26:45 Understanding Disease Cycles and Pathogen Survival
28:03 Cultural Practices: Prevention is Key
28:40 Exclusion Strategies: Clean Seeds and Equipment
29:00 Eradication and Sanitation Best Practices
29:24 Protection Strategies and Fungicide Use
29:44 Urban and Controlled Environment Agriculture Introduction
30:27 CEA Crop Diversity: Tomatoes, Lettuce, Cucumbers, Peppers
30:54 Community Gardens and Urban Food Production
31:15 CEA System Categories: Greenhouses to Vertical Farms
31:52 UGA’s Controlled Environment Agriculture Team
32:33 CEA System Classification: Cultivation Methods
33:34 Plant Diseases in CEA: Similar Pathogens, Different Management
34:44 Georgia CEA Facility Examples: Hydroponics and Vertical Systems
37:04 Disease Triangle in Controlled Environment Agriculture
38:56 Tip Burn: Abiotic Disorder in CEA Systems
39:32 Botrytis (Gray Mold): High Humidity Pathogen
40:02 Powdery Mildew in CEA: Symptoms and Management
40:29 Black Leg Disease on Basil: Plectosphaerella
41:02 Root Diseases: Pythium and Oomycete Pathogens
41:34 Pythium Species and Temperature Preferences
42:00 Sources of Contamination in Hydroponic Systems
42:32 Sanitation: The Foundation of CEA Disease Management
43:05 Thielaviopsis: Root Browning in Hydroponic Systems
44:00 Summary: Integrated Disease Management in CEA
45:00 Preventative, Diagnostic, and Management Strategies
45:58 Contact Information and Resources
46:31 Q&A Session Begins
49:31 Closing Remarks and Thank You
QUESTIONS & ANSWERS
Q: How can growers distinguish between biotic and abiotic disease problems in their crops?
A: Pattern recognition is critical for diagnosis. Abiotic problems typically produce uniform symptoms across multiple host species because environmental factors affect all plants similarly regardless of their identity. Biotic diseases show random, scattered patterns as pathogens spread from plant to plant, often affecting susceptible individuals first—similar to how illness spreads in a crowded room where those closest to the infected person or with weaker immune systems get sick first, not everyone simultaneously.
Q: What is the disease triangle and why is it important for disease management?
A: The disease triangle demonstrates that disease occurs only when three factors coincide: a susceptible host, a virulent pathogen, and favorable environmental conditions. If you can eliminate any one of these three factors, disease will not develop. This principle guides management strategies—planting resistant varieties removes the susceptible host, adjusting planting dates or irrigation practices modifies the environment, and sanitation reduces pathogen presence. Understanding this triangle allows growers to manipulate conditions and prevent disease rather than relying solely on chemical treatments.
Q: How do plant pathologists identify different fungal pathogens under the microscope?
A: Fungal identification relies on characteristic microscopic features including hyphal structure, spore morphology, and fruiting body types. For example, Rhizoctonia produces hyphae with distinctive 90-degree branching patterns. Fusarium creates banana-shaped, multicellular, colorless spores. Thielaviopsis produces dark-pigmented multicellular spores. Powdery mildew fungi form closed, spherical fruiting bodies called cleistothecia. These diagnostic features, combined with symptom patterns and host information, allow accurate pathogen identification.
Q: What are oomycetes and how do they differ from true fungi?
A: Oomycetes are fungal-like organisms previously classified as fungi but now recognized as a separate group. Common oomycete pathogens include Pythium, Phytophthora, and downy mildews. They’re called “water-loving pathogens” because they thrive in wet conditions and produce swimming spores with flagella. These organisms can produce resting spores called oospores that survive in soil for up to 40 years. Despite their fungal-like appearance and disease symptoms, oomycetes have different cell wall composition and require different management approaches than true fungi.
Q: Why is Botrytis such a common problem in controlled environment agriculture?
A: Botrytis (gray mold) thrives in the high humidity conditions often present in controlled environment systems, particularly when plant canopies are dense or ventilation is inadequate. The pathogen attacks tender, freshly injured tissues and produces gray, fuzzy spore masses. Management requires maintaining dry plant canopies through proper spacing, adequate ventilation, humidity control, and prompt removal of injured or senescent plant material. Condensation on leaves provides ideal conditions for Botrytis infection.
Q: How does powdery mildew management differ from other foliar diseases?
A: Powdery mildew is unique because it grows superficially on leaf surfaces rather than penetrating deep into tissues. It begins with irregular chlorotic (yellow) spots on upper leaf surfaces. Unlike most fungal pathogens that require free moisture, powdery mildew actually avoids water—applying water directly to leaves can help manage the disease. This pathogen thrives under high relative humidity with adequate plant spacing and proper air circulation, making environmental management more effective than chemical applications.
Q: What makes root diseases particularly challenging in hydroponic systems?
A: Hydroponic systems provide ideal conditions for water-loving oomycete pathogens like Pythium and Thielaviopsis. These pathogens produce swimming spores that move freely through the circulating water, potentially spreading to all plants in the system rapidly. Different Pythium species prefer different temperature ranges, so cooling water may control some species while favoring others—making species-level diagnosis essential. Contamination can enter through growing media, source water, tools, footwear, or outdoor air, requiring comprehensive sanitation protocols.
Q: What are the most important sanitation practices for controlled environment agriculture?
A: Never reuse growing mixes, as spent media harbors pathogens. Sweep and clean all floors regularly. Treat different surfaces appropriately—not all surfaces require the same sanitizer concentration or contact time. Sterilize tools between uses and especially between plants. Start cultural practices in healthy areas before moving to diseased sections to avoid spreading pathogens. Control entry points including seeds, media, water sources, benches, and human traffic. Monitor and manage air circulation, humidity, and plant spacing to minimize disease-favorable conditions.
Q: Should fungicides be the primary disease management strategy in CEA systems?
A: No. Chemical fungicides should be the last resort in controlled environment agriculture. Many conventional fungicides are not labeled for indoor production systems or have restricted use in enclosed spaces. Instead, prioritize integrated disease management: use resistant or tolerant varieties when available, implement rigorous sanitation protocols, optimize environmental conditions (spacing, ventilation, humidity), identify pathogens accurately before treatment, quarantine affected areas, and consider biological fungicides as an intermediate option before conventional chemistry.
Q: How does the UGA Controlled Environment Agriculture team support Georgia growers?
A: UGA has assembled a five-person CEA research team covering crop physiology (Dr. Renito Ferrazzi), plant pathology (Dr. Ruchika Kashyap), phenomics (Dr. Song), breeding (Dr. Andrew Ogden), and entomology (Dr. Eric Schuller). The team is building new research infrastructure at both Athens and Griffin campuses to conduct needs-based research directly addressing challenges faced by Georgia’s CEA industry. Growers can submit samples for disease diagnosis, participate in surveys identifying industry needs, and access extension programming tailored to controlled environment production systems.
Q: What is tip burn and how should growers manage this disorder in CEA systems?
A: Tip burn is an abiotic disorder commonly seen in lettuce and other leafy crops, often mistaken for disease. While typically attributed to calcium deficiency, it actually results from complex interactions between airflow, humidity, and transpiration rates that limit calcium movement to rapidly growing leaf tips. Management focuses on environmental optimization rather than calcium supplementation alone—improving air circulation, maintaining appropriate humidity levels, and ensuring consistent growing conditions help prevent this disorder more effectively than simply adding calcium fertilizer.
Q: How can growers determine whether to use diagnostic services for disease problems?
A: Submit samples when you observe unusual symptoms, when management strategies aren’t working as expected, when you need species-level pathogen identification for targeted management (especially important for Pythium in hydroponics), or when dealing with new or emerging diseases like black leg on basil. Accurate diagnosis prevents wasted resources on inappropriate treatments and helps identify whether problems are biotic or abiotic. The UGA Plant Disease Clinic accepts samples and Dr. Kashyap actively surveys Georgia CEA operations to build knowledge of common disease challenges in the state.
ADDITIONAL RESOURCES
Contact Information:
Dr. Ruchika Kashyap
Assistant Professor and Extension Specialist
Urban and Controlled Environment Plant Pathology
Department of Plant Pathology, University of Georgia – Athens Campus
Email: Available through UGA Extension
UGA Plant Disease Diagnostic Services:
UGA Plant Disease Clinic
Samples accepted for accurate pathogen identification and management recommendations
UGA Controlled Environment Agriculture Team:
- Dr. Rhuanito Ferrarezi – CEA Crop Physiology
- Dr. Ruchika Kashyap – CEA Plant Pathology
- Dr. Zhihang Song – CEA Phenomics
- Dr. Andrew Ogden – CEA Breeder
- Dr. Eric Schoeller – CEA Entomologist
Recommended Reading:
eGro Alert: “Root Diseases in Hydroponics” (referenced in presentation)
Available through eGro.org extension platform
Survey Participation:
Dr. Kashyap conducts ongoing surveys of controlled environment agriculture operations across Georgia to identify industry needs and disease challenges. Growers interested in participating should contact her through UGA Extension.
Topics for Future Learning:
- Integrated Pest Management in CEA systems
- Biological control options for indoor agriculture
- Water quality management in hydroponics
- Environmental optimization for disease prevention
- Resistant variety selection for controlled environments
This webinar introduced fundamental plant pathology concepts while highlighting the unique disease challenges in Georgia’s growing urban and controlled environment agriculture industry, emphasizing integrated management approaches and the importance of accurate diagnosis.