Speaker: Dr. Ping Yu, Assistant Professor and Ornamental Specialist, UGA Griffin Campus
Webinar Date: July 18, 2024
Moderator: Dr. Shimat Joseph, UGA Extension Entomologist
Duration: 49:37
NARRATIVE SUMMARY
Dr. Ping Yu delivered a comprehensive presentation on preventing soil-borne diseases in container nursery production through smart irrigation management practices. As a horticulturist specializing in ornamental production for greenhouses and nurseries, Dr. Yu emphasized that “smart irrigation” means starting to monitor water regularly and adapting good technologies to reduce soil-borne disease pressure tremendously. The presentation focused on practical, non-chemical approaches to disease management that nursery professionals can implement immediately.
Dr. Yu began by reviewing common soil-borne pathogens affecting container production, including Fusarium, Pythium (Pythium spp.), Rhizoctonia (Rhizoctonia solani), and Phytophthora (Phytophthora spp.), which cause damping-off, root rot, and vascular diseases. These pathogens thrive in wet soils with limited drainage and are significantly influenced by irrigation scheduling and substrate moisture levels. She outlined fundamental prevention strategies including avoiding wet soil and poor drainage, incorporating quality organic matter like composted hardwood or pine bark, installing French drains, and immediately removing infected plants from production areas.
The core of the presentation addressed water quality monitoring through pH and electrical conductivity (EC) measurements. Dr. Yu demonstrated the pour-through method for regular monitoring, explaining that growers can easily implement this non-destructive sampling technique using portable pH/EC meters, collection saucers, and basic data sheets with multiple replicates. For container production using water-soluble fertilizers, optimal pH ranges from 5.5 to 6.5, with EC ranging from 800 to 1500 microsiemens. She emphasized the relationship between pH and nutrient availability, noting that proper pH management prevents both nutrient deficiencies and creates less favorable conditions for pathogen development.
Dr. Yu extensively covered irrigation quantity management, explaining the importance of installing flow meters to track water usage and plan for facility expansion. She reviewed three main irrigation scheduling approaches: scheduling by feeling (the most common but least accurate low-cost method), soil moisture sensor-based systems (more accurate and labor-saving when paired with automation), and evapotranspiration-based scheduling (primarily used in field situations). Common irrigation systems for container nurseries include overhead sprinklers (most common in the Southeast but only 15-50% efficient), boom irrigation with wheels (more expensive but covers wider areas), drip irrigation for woody plants in larger containers (70-90% efficient), and supplemental hand watering for edge plants.
The presentation included detailed discussion of irrigation efficiency, defined as the ratio of water taken up by plants to water pumped or delivered. Dr. Yu explained factors influencing efficiency including plant species and size, plant spacing, canopy capture, weather conditions, and substrate properties. She introduced the canopy capture factor concept, demonstrating how mature plant canopies can reduce irrigation run times by up to 50% when the capture factor is properly calculated. Distribution uniformity (DU) received significant attention, with Dr. Yu explaining that DU values above 80% indicate excellent irrigation uniformity while values below 60% suggest highly variable application rates leading to stressed plants on container edges.
Dr. Yu provided practical checklists for irrigation system maintenance, emphasizing pre-operation inspections for leaks, missing components, and proper emitter selection, plus post-operation checks for clogged nozzles, valve malfunctions, and minimized overspray to non-production areas. The take-home messages stressed regular monitoring of pH and EC, using flow meters for water tracking, checking for system malfunctions, and periodically measuring efficiency and uniformity.
As a bonus topic, Dr. Yu introduced dissolved oxygen monitoring in irrigation systems, sharing insights from the Cultivate trade show. She explained that dissolved oxygen levels above 8 ppm promote healthier plant growth and facility management. Preliminary data from major producers like Metrolina Greenhouses demonstrates that super-saturated dissolved oxygen can reduce production time for ornamental crops. While dissolved oxygen monitoring remains uncommon in ornamental production, Dr. Yu encouraged awareness of this emerging technology for disease management and improved plant health.
During the question-and-answer session, Dr. Yu discussed her current research program including substrate sustainability studies, water use efficiency trials with different growing media, propagation research on tea olive (Osmanthus fragrans) examining environmental factors affecting flowering, collaborative work on invasive pest management for ornamentals, and biochar substrate effects on disease suppression in ornamental production. When asked about top horticultural issues facing Georgia nurseries, she identified irrigation management, substrate selection and plant variety choices, and weed management as the three primary concerns for southeastern growers.
YOUTUBE TIMESTAMPS
0:00 Introduction and Webinar Overview
0:10 Speaker Introduction: Dr. Ping Yu
1:03 Presentation Title and Smart Irrigation Concept
1:52 Actions and Results Framework
2:15 Key Questions for Growers
2:41 Presentation Content Overview
3:27 Soil-borne Diseases Basics
4:01 Common Container Diseases: Damping-off and Root Rot
4:38 Pathogen Requirements and Moisture Levels
5:09 How Diseases Start: Wet Soils and Poor Drainage
5:38 Disease Reduction Strategies
6:16 Incorporating Organic Matter
6:46 Water as a Disease Factor
7:02 Water Quality Monitoring: pH and EC
7:37 Why Monitor Water Quality?
8:04 pH and Nutrient Availability Relationships
8:49 Container as Buffer Zone Concept
9:19 Collecting Water Samples
10:03 Water Sample Sources
10:52 Water Analysis Reports
11:12 Pour-through Method Introduction
12:13 Materials Needed for pH/EC Monitoring
13:01 Data Sheet Setup and Replicates
13:37 Pour-through Method Steps
14:26 Recording and Analyzing Results
15:03 Interpreting pH and EC Values
16:27 Fertigation System Setup
17:10 Water Quantity Monitoring
17:52 Flow Meters for Water Tracking
18:24 Planning for Facility Expansion
19:29 Daily Irrigation Scheduling Methods
19:39 Irrigation Scheduling by Feeling
20:06 Feeling Method: Advantages and Limitations
20:47 Lifting Container Weight Assessment
21:04 Soil Moisture Sensor-based Scheduling
21:34 Sensor Advantages: Labor Savings and Accuracy
21:46 Sensor Disadvantages: Calibration and Cost
22:07 Automated Irrigation with Sensors
22:37 ET-based Irrigation Scheduling
23:06 Overhead Sprinkler Systems
23:41 Boom Irrigation Systems
24:07 Moving Boom with Wheels
24:27 Hand Watering Supplement
25:04 Drip Irrigation for Woody Plants
25:17 How to Become an Efficient Irrigator
25:45 Irrigation Efficiency Definition
26:20 Distribution Uniformity Definition
26:49 Uniformity Issues: Edge Plant Problems
27:10 Irrigation System Efficiency Numbers
27:46 Micro-irrigation vs. Overhead Efficiency
28:20 Causes of Low Irrigation Efficiency
29:14 Factors Influencing Efficiency
29:52 Plant Species and Size Considerations
30:31 Plant Spacing Effects
30:58 Canopy Capture Effects
31:20 Weather and Substrate Influences
31:42 Additional Resources on Efficiency
31:45 Canopy Capture Factor Measurement
32:24 Capture Factor Formula
32:36 Canopy Factor Implications
33:01 Reducing Irrigation Run Time
33:42 Irrigation System Efficiency Checks
34:05 Pre-operation Inspection Checklist
34:27 Missing Components Check
34:29 Post-operation Checks
34:41 Orientation and Location Verification
34:49 Clogged Nozzles and Valve Malfunctions
35:00 Minimizing Non-production Area Watering
35:25 Homeowner Irrigation Efficiency Issues
35:38 Distribution Uniformity Introduction
36:00 Low vs. High DU Values
36:18 Uniformity and Plant Stress
36:51 Causes of Low Uniformity
37:21 Measuring Distribution Uniformity
37:39 Cup Test Procedure
38:05 DU Formula and Target Values
38:13 Visual DU Measurement Method
38:34 Rain Gauge Placement
38:35 Take-home Messages Summary
38:43 Monitor pH and EC Regularly
38:48 Use Flow Meters
38:53 Check for System Malfunctions
39:00 Check Efficiency and Uniformity
39:08 Bonus Topic: Dissolved Oxygen
39:23 Dissolved Oxygen Range for Greenhouse Production
39:36 Why Dissolved Oxygen Matters
40:09 Disease Prevention Through Water Quality
40:29 Irrigation Water Contamination
41:09 Root Development and Respiration Benefits
41:38 Metrolina Greenhouse Research
41:56 Production Time Reduction Benefits
42:14 Presentation Conclusion
42:16 Q&A Session Introduction
42:36 Wait Time for Questions
43:04 Current Research Projects Discussion
43:16 Substrate Sustainability Research
43:35 Water Use Efficiency Studies
44:04 Propagation Research Overview
44:24 Tea Olive Research Focus
44:53 Osmanthus Flowering Studies
45:14 Upcoming Collaborative Projects
45:41 Invasive Pest IPM Development
46:01 Biochar and Disease Suppression Research
46:26 Dissolved Oxygen Awareness in Industry
47:00 Top Horticultural Issues in Georgia
47:21 Substrate and Plant Variety Concerns
47:31 Water and Irrigation Priority
47:47 Weed Management Challenges
48:02 Three Main Horticultural Issues Summary
48:28 No Questions from Audience
48:48 Session Conclusion
49:05 Break and Next Speaker Transition
49:37 Session End
QUESTIONS & ANSWERS
Q: What is the “smart irrigation” concept that Dr. Yu emphasizes throughout this presentation?
A: Smart irrigation means starting to monitor your water regularly and adapting good technologies for watering to reduce soil-borne diseases in nursery production tremendously. It involves systematic monitoring of both water quality (pH and EC) and water quantity (flow rates and distribution), combined with regular checks of irrigation system efficiency and uniformity to prevent the wet soil conditions that favor pathogen development.
Q: Which soil-borne pathogens are most commonly problematic in container production?
A: The most common soil-borne diseases in containers include damping-off caused by Fusarium, Pythium, and Rhizoctonia, as well as root rot caused by Phytophthora. These pathogens also include vascular wilt fungi and nematodes. They cause symptoms including wilting, collapsed growth, root decay, lesions at the soil line, and sudden plant death. These pathogens have specific moisture requirements and occur in wet soils with limited drainage or overwatered areas.
Q: How can growers easily monitor water quality in their production facilities?
A: Growers can use the pour-through method, which is non-destructive and can be performed at any time without damaging plants. Materials needed include a portable pH/EC meter, calibration solutions, collection saucers or trays, and a data sheet. The process involves irrigating representative containers, waiting 30 minutes, placing saucers underneath, adding water to collect leachate (about 50 ml per sample), and measuring pH and EC. Use at least three replicates for statistically valid results.
Q: What are the optimal pH and EC ranges for container production using water-soluble fertilizers?
A: For container production using water-soluble fertilizers or combination fertilizers (water-soluble plus controlled-release), the optimal pH range is 5.5 to 6.5, with EC ranging from 800 to 1500 microsiemens. For production using only controlled-release fertilizer, the pH range remains 5.5 to 6.5, but the EC range is lower at 500 to 1000 microsiemens. These ranges optimize nutrient availability while minimizing conditions favorable for pathogen development.
Q: Why is it important to install flow meters in nursery irrigation systems?
A: Flow meters allow growers to track exactly how much water is used for specific seasons and production areas. This data is critical for facility expansion planning—growers can calculate water needs for new production areas based on historical usage patterns. For example, if two acres use 1,000 gallons per day, growers can accurately estimate water requirements and infrastructure needs for expanded production sites.
Q: What are the three main methods for irrigation scheduling in container production?
A: The three main scheduling methods are: (1) Scheduling by feeling—using hand touch to assess soil moisture and lifting containers to judge weight, which is low cost but requires experience and has low accuracy; (2) Soil moisture sensor-based scheduling—using sensors inserted into containers for automated monitoring, which is more accurate and labor-saving but requires frequent calibration and sensors can be expensive; (3) ET-based scheduling—using evapotranspiration measurements, which is more commonly used in field situations rather than container production.
Q: How efficient are different irrigation systems used in container nurseries?
A: Sprinkler irrigation systems for container nurseries typically achieve only 15-50% efficiency with an average of 20%, because approximately half the water goes to the ground rather than containers. Drip or line source systems achieve 70-90% efficiency with an average of 85%. Spray systems achieve 70-85% efficiency with an average of 80%. Micro-irrigation systems (drip and spray) are significantly more efficient because they deliver water directly to plants without waste to non-plant areas.
Q: What is canopy capture factor and why does it matter for irrigation management?
A: Canopy capture factor measures how much irrigation water is captured by the plant canopy and directed into the container versus water that goes directly into the substrate. If the capture factor is greater than one, the plant canopy is capturing additional water into the container. A capture factor of two means irrigation run time can be reduced by 50% compared to containers without plants. Understanding capture factor helps optimize irrigation scheduling as plants mature and develop fuller canopies.
Q: What is distribution uniformity (DU) and what values indicate good irrigation performance?
A: Distribution uniformity measures how evenly water is applied across an irrigation area. Low DU (below 60%) indicates very different application rates across the production area, leading to stressed plants (typically on container edges). High DU (above 80%) indicates similar application rates and even water distribution to all plants. Achieving DU above 80% makes a grower an excellent irrigator. Poor uniformity is a major cause of plant stress and creates conditions where some plants are overwatered (favoring disease) while others are underwatered.
Q: What should growers check to maintain efficient irrigation systems?
A: Before turning on irrigation, check for leaks or emitter malfunctions, missing components like nozzles or emitters, and ensure nozzles within the same zone are identical (except when compensating for slope or elevation changes). After turning on irrigation, verify the orientation and location of emitters, ensure nozzle rotation and water trajectory are similar, check for clogged nozzles and valve malfunctions, and minimize watering of roads and non-production areas. Regular system checks prevent efficiency losses from equipment failures.
Q: What is dissolved oxygen and why is it important for irrigation water quality?
A: Dissolved oxygen in irrigation water typically ranges from 5-8 ppm, with levels above 8 ppm being optimal for greenhouse production. Monitoring dissolved oxygen is important because it helps maintain healthy facilities and improves plant growth. Contaminated irrigation or pond water can contain bacteria or fungi that travel through pipelines to plants, impacting plant health. Dissolved oxygen also affects root respiration rates and root development. Preliminary research from major producers like Metrolina Greenhouses shows that super-saturated dissolved oxygen in irrigation systems can reduce production time for ornamental plants.
Q: What current research is Dr. Yu conducting related to irrigation and disease management?
A: Dr. Yu has students researching substrate sustainability levels with different growing media for container production and water use efficiency across various substrates. She is also investigating propagation of tea olive (Osmanthus fragrans) and environmental factors like cold and darkness affecting flowering. Upcoming collaborative projects include developing IPM strategies for invasive pests on ornamentals and studying biochar substrates’ effects on disease suppression in ornamental production through a proposal submitted to the Horticultural Research Institute.
Q: What are the top horticultural issues facing nursery growers in Georgia and the Southeast?
A: The three main horticultural issues Dr. Yu has identified from Georgia growers are: (1) Irrigation management—the most critical issue; (2) Substrates and plant variety selection—growers are seeking different substrate types and diverse ornamental plant options; and (3) Weed management—an ongoing challenge in production. Fertilizer management is less problematic, and marketing issues vary by individual operation. These priorities reflect broader southeastern regional concerns beyond just Georgia.
ADDITIONAL RESOURCES
For More Information on Irrigation Efficiency:
YouTube video link referenced in presentation covering factors influencing irrigation efficiency in detail
For Canopy Capture Factor:
Additional reference materials mentioned for detailed capture factor calculations and applications
UGA Extension Contacts:
- Dr. Ping Yu, Assistant Professor and Ornamental Specialist, UGA Griffin Campus
- Dr. Shimat Joseph, Extension Entomologist, UGA Griffin Campus
- Dr. Jean Williams-Woodward, Plant Pathologist (for detailed pathogen information)
Water Testing:
- UGA Soil, Plant, and Water Laboratory (Athens, Georgia)
- Contact local UGA Extension agents for sample collection assistance
Trade Show Information:
- Cultivate (annual green industry trade show) for latest irrigation technologies and industry innovations
This webinar provides practical, science-based strategies for reducing soil-borne diseases through smart irrigation management in container nursery production. For questions about ornamental horticulture and irrigation management, contact Dr. Ping Yu at the University of Georgia Griffin Campus.