Speaker: Dr. Fereshteh Angel Shahoveisi, Turfgrass Pathologist, University of Maryland
Webinar Date: September 19, 2024
Duration: 51:18
CEU Categories: Category 24 (Ornamental and Turf Pest Control), Category 35 (Industrial, Institutional, Structural and Health Related Pest Control)
NARRATIVE SUMMARY
Dr. Angel Shahoveisi, a turfgrass pathologist at the University of Maryland, delivered a comprehensive presentation on research-based management strategies for three critical turfgrass diseases affecting landscape, lawn, and sports turf environments. Drawing from both historical research and current extension trials, Dr. Shahoveisi provided practical guidance grounded in scientific evidence for pest management professionals seeking effective disease control approaches.
The presentation opened with foundational pathology concepts, introducing the disease triangle and the importance of time as a fourth critical factor for disease establishment. Dr. Shahoveisi carefully distinguished between disease symptoms (plant reactions to pathogens) and signs (visible pathogen structures), emphasizing this distinction aids accurate field diagnosis. She presented survey results from mid-Atlantic landscape managers identifying brown patch as their most challenging disease concern, followed by red thread and dollar spot, establishing the practical relevance of her topic selection.
Dr. Shahoveisi thoroughly compared brown patch and large patch, two diseases caused by different strains of Rhizoctonia solani. Brown patch affects cool-season grasses like tall fescue, Kentucky bluegrass, and creeping bentgrass during hot, humid summer conditions when temperatures exceed 70°F at night and 90°F during the day. Large patch targets warm-season grasses, particularly zoysiagrass and bermudagrass, during spring and fall shoulder seasons as grasses enter or emerge from dormancy. She detailed identification features including irregular tan lesions with brown borders for brown patch, distinctive 90-degree angle mycelium under microscopic examination, and the characteristically larger patch sizes that distinguish large patch from brown patch.
Cultural management recommendations centered on leaf wetness reduction as the primary control strategy. Dr. Shahoveisi emphasized early morning irrigation timing, improving air circulation through pruning in shaded areas, and maintaining thatch below 0.5 inches. She clarified critical distinctions about nitrogen fertilization timing—excessive nitrogen during active brown patch periods (mid-summer) exacerbates disease, while excessive fall/spring nitrogen worsens large patch. She presented University of Maryland research demonstrating that microbial inoculants like BioFlex combined with moderate nitrogen fertilization can significantly reduce brown patch compared to untreated controls, though not to the level achieved by chemical fungicides. A North Carolina State University study revealed tall fescue can receive summer nitrogen fertilization at modest rates (1-3 pounds per year) without increasing brown patch, but rates of 4-6 pounds significantly increased disease severity.
Gray leaf spot management occupied the presentation’s final section, addressing this increasingly important pathogen on both traditional hosts like St. Augustinegrass and perennial ryegrass and emerging concerns on tall fescue. Dr. Shahoveisi described characteristic small, purplish lesions that develop tan centers with darker borders, the distinctive fishhook leaf tip symptom, and the pathogen’s (Pyricularia species) requirement for 10-12 hours of leaf wetness and night temperatures above 70°F. She emphasized cultivar resistance as the primary management strategy, referencing National Turfgrass Evaluation Program (NTEP) data showing dramatic differences in susceptibility among varieties. Fungicide management discussion included warnings about QoI fungicide resistance in gray leaf spot populations, with efficacy ratings varying from 1 to 4 depending on local resistance development. Research from Penn State demonstrated silicon amendments (wollastonite) could reduce gray leaf spot, though practical adoption by practitioners remains limited.
The presentation concluded with integrated disease management philosophy, advocating exhausting cultural and biological control options before resorting to chemical applications, particularly in landscape settings where client patience permits. Dr. Shahoveisi acknowledged the practical realities facing landscape professionals who must balance scientific recommendations with client expectations. During the Q&A session, she discussed ongoing research using autonomous mowers equipped with UVC light for dollar spot management, collaborative genetics work with Penn State, Texas A&M, and Oklahoma breeding programs, and realistic fungicide application schedules for gray leaf spot on St. Augustinegrass in southern regions.
YOUTUBE TIMESTAMPS
0:00 Introduction and Speaker Credentials
1:14 Webinar Scope: Landscape and Sports Turf Focus
2:04 Topics Overview: Disease Triangle to Management
2:45 Rhizoctonia Diseases and Gray Leaf Spot Preview
3:15 Disease Triangle: Pathogen, Host, Environment
4:03 Temperature Ranges and Dollar Spot Example
4:52 Time as the Fourth Disease Factor
5:18 Symptoms vs. Signs: Critical Definitions
6:00 Signs: Mycelium and Spore Structures
7:04 Mid-Atlantic Disease Survey Results
7:24 Brown Patch: Number One Challenge
8:00 Gray Leaf Spot: Emerging Issue on Tall Fescue
8:36 Brown Patch and Large Patch Introduction
8:41 Rhizoctonia solani: Same Species, Different Diseases
9:05 Host Differences: Cool vs. Warm Season Grasses
9:34 Brown Patch Identification: Leaf Lesions
10:15 Comparing Pythium Blight and Brown Patch
11:02 Mycelium Characteristics Under Microscope
11:32 90-Degree Angle Mycelium: Diagnostic Feature
11:51 Favorable Conditions: Hot and Humid
12:23 Temperature Thresholds for Brown Patch
12:49 Leaf Wetness Requirements: 10+ Hours
13:06 Irrigation Timing and Dew Management
13:33 Air Movement and Shade Considerations
13:51 Nitrogen and Brown Patch: The Right Balance
14:25 Large Patch: Formerly Brown Patch
14:36 Biological Differences Between Disease Groups
14:57 Large Patch Timing: Spring and Fall Dormancy
15:19 Zoysiagrass vs. Bermudagrass Susceptibility
15:32 Maryland Observations: April to June
15:57 Thatch Management for Large Patch
16:11 Over-Irrigation Concerns
16:22 Mowing Height Recommendations
16:42 Nitrogen Timing for Large Patch
17:05 Comparing Brown Patch and Large Patch
17:29 Size Differences: Why “Large Patch”
17:50 Molecular Strain Differences
18:04 Cultural Management: Integrated Approach
18:10 Leaf Wetness Management Priority
18:25 Pruning and Sunlight Penetration
18:34 Aeration and Drainage for Persistent Issues
18:52 Early Morning Irrigation Timing
19:00 Infrequent but Deep Watering
19:13 Thatch Control: Below 0.5 Inch
19:26 Chemical Applications: When Necessary
19:43 University of Kentucky Fungicide Guide
19:53 FRAC Groups and Resistance Management
20:10 Research-Based Efficacy Ratings
20:40 Heritage and Propiconazole for Lawns
21:03 Velista: Effective for Large Patch Only
21:26 Label vs. Research Efficacy
21:52 2022 Brown Patch Trial Results
22:08 Experimental Fungicides: Future Promise
22:49 Research Recommendations Overview
22:55 Microbial Inoculants Study: Brown Patch
23:06 BioNutrients and BioFlex Products
23:11 Bullseye Tall Fescue Trial Design
23:22 Nitrogen Fertilization Combinations
23:34 Six-Week Application Schedule
23:38 Data Collection: Severity, Quality, Color
23:49 Experimental Design with Fungicide Comparisons
24:07 Nitrogen Rate Variables: 25% to 100%
24:24 BioFlex as Standalone Treatment
24:34 Four Replications for Statistical Power
24:41 Brown Patch Severity Results (AUDPC)
24:56 Treatment Comparison: Fungicide vs. Biological
25:27 BioFlex: Significant Reduction Without Fungicide
25:40 Biological Control Effectiveness Levels
26:04 NPK Formulation: 7-0-5 in BioFlex
26:13 Turfgrass Quality Results
26:18 Disease and Quality Correlation
26:38 Color Results: Minimal Differences
26:55 Study Summary: When to Use Biological Control
27:10 Less Severe Situations: Biological Applications
27:35 NC State Study: Multiple Management Factors
27:45 Nitrogen Rate, Timing, and Rainfall Effects
28:04 Nitrogen Application Timing Study
28:15 One, Two, Three Pounds Per Year: No Difference
28:28 Statistical Analysis: Letter Groupings
28:40 Four, Five, Six Pounds: Disease Increase
28:59 Defining “Excessive Nitrogen”
29:09 Simulated Rainfall Effects
29:20 2015 and 2016 Replication
29:31 No Negative Effects from Rainfall
29:38 Urea Application Timing Combinations
29:52 March, September, November Treatments
30:06 No Significant Timing Differences
30:25 Application Equipment Comparison
30:40 Backpack vs. Commercial Sprayers
30:56 Equipment: No Difference in Efficacy
31:02 2013 Large Patch Study
31:09 Limited Recent Cultural Practice Research
31:20 Verticutting and Aeration Treatments
31:32 Nitrogen Timing: Summer vs. Spring/Fall
31:45 Fall/Spring Nitrogen: Disease Increase
31:51 2008 Summer vs. Spring/Fall Comparison
32:04 Inconsistent Results Across Years
32:18 Gray Leaf Spot Introduction
32:22 Spore Production Characteristics
32:26 Lesion Characteristics: Small and Purplish
32:37 Tan Centers with Dark Brown Borders
32:46 Fishhook Leaf Tip: Don’t Rely Solely
33:02 Always Confirm with Lesion Observation
33:07 Perennial Ryegrass Example
33:13 Rapid Canopy Death Potential
33:26 Favorable Conditions: Night Temps Above 70°F
33:38 Day Temperature: 80-90°F Range
33:45 High Humidity Requirements
33:51 Leaf Wetness for Spore Germination
33:57 Avoid Heavy Summer Nitrogen
34:04 1990s: Major Issue on Perennial Ryegrass
34:09 Golf Course Shift to Bentgrass
34:16 Current Status: Less Prevalent
34:22 Emerging Issue: Gray Leaf Spot on Tall Fescue
34:29 Golf Course Rough Area Diagnosis
34:36 Laboratory Confirmation with Spores
34:47 Comparing Gray Leaf Spot and Brown Patch
35:02 Spindle-Shaped vs. Irregular Lesions
35:07 Leaf Edge or Middle Placement
35:19 Water Droplet-Shaped Spores
35:32 St. Augustinegrass: Major Host
35:44 Gray Leaf Spot vs. Leaf Spot Diseases
35:49 Curvularia and Bipolaris Pathogens
36:01 Circular vs. Spindle Lesion Shapes
36:08 Microscopic Spore Examination
36:19 Similar Management Approaches
36:24 Label Verification for Both Diseases
36:35 Leaf Spot: Saprophytic Nature
36:46 Stressed Turf and Dead Tissue
36:56 Landscape Settings: Fungicides Rarely Needed
37:08 Temperature Differences: Cool vs. Hot/Humid
37:14 Wide Host Range for Leaf Spot
37:30 Management Priority: Resistant Cultivars
37:38 1990s Research: Cultivar Development
37:46 Current Availability: Good Resistant Options
37:51 Seedling Stage Susceptibility
37:58 First 2-4 Weeks: Critical Monitoring
38:05 Avoid High Summer Nitrogen
38:14 July, August, September Applications
38:24 Slow-Release Nitrogen in Fall Alternative
38:37 Deep, Infrequent Watering Strategy
38:48 Reduce Overhead Irrigation
38:56 Kentucky Fungicide Guide Reference
39:07 QoI Fungicides: FRAC Group 11
39:17 Efficacy Ratings: 1 (Low) to 4 (High)
39:27 Heritage: Variable Efficacy (1-4)
39:34 QoI Resistance Development
39:42 Population-Level Resistance
39:49 Turf Farm Gray Leaf Spot Trial
39:57 Severe Disease Pressure Example
40:08 Cultivar Susceptibility Impact
40:18 Rapid Stand Death Potential
40:29 2005 Cultivar Resistance Study
40:37 Cultivar Differences Without Fungicides
40:52 NTEP: National Turfgrass Evaluation Program
41:02 Renovation Decisions: Choose Resistant Varieties
41:22 1990s/Early 2000s Research Focus
41:34 Mowing Height and Nitrogen Study
41:44 Two Mowing Heights Tested
41:55 Monthly Nitrogen Applications
42:04 No Mowing Height Effect
42:14 Nitrogen Effect: Significant
42:19 Highest Rate: More Disease
42:32 Multiple Studies Support Nitrogen-Disease Link
42:39 Penn State Silicon Study (2008)
42:45 Peat/Sand Mix vs. Silt Loam
42:56 Silicon Sources: Wollastonite vs. Calcium Silicate
43:06 Gray Leaf Spot Reduction with Wollastonite
43:14 Soil Type: No Effect on Results
43:19 Silicon Management: Innovative Approach
43:25 Limited Practitioner Adoption
43:33 Summary: Disease Triangle Plus Time
43:45 Susceptible Host and Virulent Pathogen
43:55 Brown Patch and Large Patch: Same Species
44:02 Different in Many Important Ways
44:09 Cultural Practices: Similarities and Differences
44:16 Gray Leaf Spot: Cool and Warm Season Issue
44:21 Adapted Pathogen: Multiple Hosts
44:38 Research Results: Cultural Practice Importance
44:52 Less Effective Than Fungicides
45:01 Lower Disease Levels: Cultural Methods Work
45:10 Critical Question: Are Chemicals Necessary?
45:16 Exhaust Cultural Practices First
45:22 Landscape and Lawns: Time and Patience
45:29 Biological Control Options
45:36 Practitioner Realities: Client Expectations
45:43 Moving Parts in Decision Making
45:50 Integrated Disease Management: Best Practice
45:58 Biological, Cultural, Mechanical, Chemical Combination
46:07 Q&A Session Introduction
46:23 Current Research Projects Overview
46:34 Extension: Fungicide Trials
46:41 Gray Leaf Spot, Brown Patch, Dollar Spot
46:46 Research Focus: Dollar Spot and Brown Patch
46:53 UVC on Autonomous Mowers Study
47:03 Promising Field Results
47:08 Mother Nature Challenges
47:14 Machine Learning and AI Applications
47:22 Disease and Nematode Identification
47:31 Basic Research vs. Applied Extension
47:46 Genetic Resistance Collaborations
47:54 Penn State, Texas A&M, Oklahoma Breeders
48:01 No Breeder at University of Maryland
48:05 Breeding Program Partnerships
48:12 Genome-Wide Association Panels
48:17 Bermudagrass, Zoysiagrass, Creeping Bentgrass
48:26 Field and Greenhouse Testing
48:33 Large Patch and Dollar Spot Response
48:38 Zoysiagrass Data Collection
48:48 Analysis Timeline: Next Year
48:59 Q&A: St. Augustinegrass Fungicide Applications
49:13 GLS Control: Five to Seven Applications
49:20 Year-Dependent Disease Pressure
49:29 Delayed Disease in 2024
49:38 Early vs. Late Season Onset
49:43 Four to Five Applications: Typical
49:52 Six to Seven: Earlier Disease Years
50:00 Maryland Sweet Spot: Late June Start
50:06 Southern Regions: Earlier Timing
50:11 Two to Three Week Application Intervals
50:20 Realistic Application Numbers
50:31 Storm Patterns and Spore Movement
50:38 Spores from Southern States
50:43 Florida Storm Tracking
50:56 2024: No Disease from Storms
51:05 Anticipation vs. Guarantee
51:13 Closing Thanks and Conclusion
QUESTIONS & ANSWERS
Q: What are the key differences between brown patch and large patch that practitioners should know?
A: Brown patch affects cool-season grasses during hot, humid summer months, while large patch affects warm-season grasses like bermudagrass and zoysiagrass during spring and fall shoulder seasons. They’re caused by different strains of Rhizoctonia solani, have different sized patches (large patch forms bigger patches), and require different fungicide selections. Nitrogen management timing also differs—avoid excessive summer nitrogen for brown patch, but avoid excessive fall/spring nitrogen for large patch.
Q: How can leaf wetness management help control Rhizoctonia diseases?
A: Leaf wetness management is the number one cultural practice for both brown patch and large patch. Water early in the morning so the canopy dries before evening, avoid late afternoon irrigation, improve air circulation through pruning in shaded areas, and water infrequently but deeply (4-6 inches). The pathogen needs more than 10 hours of leaf wetness to cause infection, so reducing dew and moisture on the canopy directly interrupts the disease cycle.
Q: Can biological control products effectively manage brown patch without fungicides?
A: University of Maryland research showed that BioFlex (a microbial inoculant with 7-0-5 NPK fertilizer) significantly reduced brown patch severity compared to non-treated controls when no chemical fungicide was applied. However, biological control didn’t provide the same level of disease suppression as chemical fungicides. Biological products work best in less severe disease situations where complete control isn’t critical, offering a middle ground between doing nothing and full chemical management.
Q: What nitrogen fertilization rates can tall fescue safely receive during summer without increasing brown patch?
A: North Carolina State research demonstrated that tall fescue can receive 1-3 pounds of nitrogen per year during summer months without significantly increasing brown patch disease compared to non-treated controls. However, when rates increased to 4-6 pounds per year, disease severity increased significantly. The key is modest fertilization rates—excessive nitrogen (above 3 pounds annually) during brown patch-favorable conditions will worsen the disease.
Q: Does rainfall shortly after fungicide application reduce effectiveness for brown patch control?
A: Research simulating rainfall 10-15 minutes after fungicide application found no negative effect on disease management outcomes. The study tested multiple fungicides in 2015 and 2016 with consistent results. This suggests practitioners don’t need to delay applications due to imminent rain concerns, though maintaining good coverage during application remains important.
Q: Why is gray leaf spot becoming more common on tall fescue?
A: Gray leaf spot traditionally affected perennial ryegrass in the 1990s and St. Augustinegrass, but the pathogen appears to be adapting to tall fescue as a host. Dr. Shahoveisi confirmed gray leaf spot on tall fescue samples from golf course rough areas through laboratory spore examination. This emerging host expansion means tall fescue managers should monitor for characteristic small purplish lesions that develop tan centers, particularly during hot, humid conditions with prolonged leaf wetness.
Q: What are the warning signs that a gray leaf spot population may be resistant to QoI fungicides?
A: Efficacy ratings for QoI fungicides like Heritage range from 1 (very low) to 4 (highest) depending on whether resistance has developed in local populations. If you apply a QoI fungicide and see no disease control effect despite proper application and coverage, your gray leaf spot population may have developed resistance. Not all populations are resistant, but resistance is documented in some areas. Rotating to different FRAC groups and following resistance management guidelines is critical.
Q: How important is cultivar selection for gray leaf spot management?
A: Cultivar resistance is arguably the number one management strategy for gray leaf spot. Research from 2005 showed dramatic differences in disease susceptibility among perennial ryegrass cultivars even without any fungicide applications. When establishing new areas or renovating, selecting resistant cultivars based on National Turfgrass Evaluation Program (NTEP) data can reduce or eliminate the need for fungicide applications. Seedling-stage turf (first 2-4 weeks) is most vulnerable regardless of cultivar, requiring close monitoring.
Q: What innovative disease management strategies are currently being researched at University of Maryland?
A: The program is testing UVC light mounted on autonomous mowers for dollar spot management, with promising field results despite Mother Nature challenges. They’re also applying machine learning and AI to identify turfgrass diseases and nematodes. On the genetics side, Dr. Shahoveisi collaborates with Penn State, Texas A&M, and Oklahoma breeding programs testing genome-wide association panels of bermudagrass, zoysiagrass, and creeping bentgrass for resistance to large patch and dollar spot, with zoysiagrass data analysis expected within the next year.
Q: Is it realistic to apply five to seven fungicide applications for gray leaf spot control on St. Augustinegrass?
A: Yes, that number is realistic but depends on the specific year’s disease pressure and timing. If gray leaf spot onset occurs in early to mid-July and persists through September-October, four to five applications may suffice. In years with earlier disease onset, six to seven applications may be necessary. For Maryland conditions, starting applications in late June provides good coverage, but southern regions may need earlier timing. Applications should be spaced every two to three weeks depending on the fungicide used.
Q: Can silicon amendments help manage gray leaf spot?
A: Penn State research from 2008 demonstrated that wollastonite (a silicon source) reduced gray leaf spot disease regardless of soil type (peat/sand mix or silt loam). Calcium silicate also showed some effect. However, it’s unclear how widely practitioners use silicon amendments as a management practice. This represents an innovative cultural approach that could complement other management strategies, though more research and practical experience would be valuable for landscape and lawn applications.
Q: Should practitioners always try cultural practices before resorting to chemical fungicides?
A: Yes, particularly for landscape and lawn settings where complete disease elimination isn’t critical. Exhaust recommended cultural practices first—irrigation timing, leaf wetness management, appropriate nitrogen rates and timing, thatch management, and consider biological control products. If these don’t provide acceptable results after giving them adequate time, then chemical management is justified. However, practitioners must balance this ideal approach with client expectations and business realities, as clients sometimes cannot wait to see if cultural practices work.
ADDITIONAL RESOURCES
Publications Referenced:
- Chemical Control of Turfgrass Diseases (University of Kentucky, 2024) – Research-based fungicide efficacy guide with FRAC groups and application intervals
Speaker Contact:
Dr. Angel Shahoveisi
Turfgrass Pathologist
University of Maryland
Department of Plant Science and Landscape Architecture
Research Collaborations:
- Penn State University (breeding program)
- Texas A&M University (breeding program)
- Oklahoma State University (breeding program)
Recommended Resources:
- National Turfgrass Evaluation Program (NTEP) – Cultivar resistance data
- University of Maryland Extension – Turfgrass disease management publications
Study Locations:
- University of Maryland Turf Farm
- North Carolina State University (2019 brown patch study)
- Large patch research (2013)
- Penn State University (2008 silicon study)
- Gray leaf spot research (2005 cultivar study, late 1990s cultural practices)