Understanding Tree Pests: Disease Interactions, Invasive Threats, and Management Strategies | GTBOP Webinar Series
Dr. Ignazio Graziosi, Assistant Professor in the Warnell School of Forestry and Natural Resources at the University of Georgia, presents a framework for understanding tree pest damage through ecological interactions. Using the disease triangle and spiral of tree decline, he examines how the pest, host tree, and environment interact to produce damage — particularly in stressful urban settings.
Three case studies illustrate different ecological scenarios: the emerald ash borer (EAB), a non-native pest devastating native ash; crapemyrtle bark scale (CMBS), a non-native pest on non-native crapemyrtle; and the orange-striped oakworm moth, a native pest on native oaks. For each, Dr. Graziosi explores host susceptibility, environmental factors, natural enemies, and chemical and biological control strategies, providing a practical decision-making framework for landscape professionals.
Presented January 15, 2026 | Getting the Best of Pests (GTBOP) Webinar Series | Green & Commercial
Hosted by the UGA Center for Urban Agriculture
Moderator: Dr. Bodie Pennisi, UGA Horticulturist
⏱️ TIMESTAMPS
0:00 Introduction and speaker credentials
1:28 The disease triangle: pest, tree, and environment
3:02 The spiral of tree decline
6:07 Native vs. non-native pest and tree interactions
7:22 Example 1: Emerald ash borer (EAB) — overview
8:23 EAB life cycle and damage symptoms
10:48 EAB generation time and temperature effects
11:57 EAB spread across North America and firewood
13:47 EAB in Georgia and native ash species diversity
15:26 White fringetree as alternate EAB host
16:43 Global trade and non-native species introductions
18:20 The invasion curve: detection, eradication, and control
28:01 Native natural enemies and the goal of balance
29:42 Example 2: Crapemyrtle bark scale (CMBS) — overview
31:47 CMBS biology, life cycle, and overlapping generations
33:47 CMBS invasion timeline and early detection
35:02 CMBS and the invasion curve in Georgia
36:06 CMBS host range expansion in North America
36:42 Urban heat island effects on scales
37:28 Chemical control options for CMBS
38:31 Natural enemies: lady beetles and lacewings
42:04 Balancing chemical and biological control for CMBS
42:25 Example 3: Orange-striped oakworm moth — overview
43:53 Oakworm life cycle and seasonal timing
44:51 Why urban and clonal trees are vulnerable
46:35 Natural enemies of the oakworm
47:56 Control decisions: damage thresholds and Btk
49:19 Presentation wrap-up and key takeaways
50:01 Moderator comments on CMBS expansion in Georgia
❓ Q&A HIGHLIGHTS
Q: What is the disease triangle?
A: Damage results from the interaction of the pest, the host tree, and the environment — not the pest alone.
Q: How does firewood spread the emerald ash borer?
A: Infested firewood was the primary pathway for EAB's rapid spread, closely matching the highway system and leading to the "Don't Move Firewood" campaign.
Q: Why is trunk injection ineffective for crapemyrtle bark scale?
A: Crapemyrtle absorbs systemic insecticides very slowly. Soil drench, soil injection, and foliar sprays are recommended instead.
Q: When should you treat for orange-striped oakworm?
A: The threshold is about 25% defoliation. Late-season defoliation is less harmful. Btk is effective against young larvae with minimal impact on natural enemies.
📚 RESOURCES
• Submit sign-in sheets for CEU credit: gtbop@uga.edu
• iTree tools for calculating tree benefits: itreetools.org
• QR codes for UGA extension publications on EAB and CMBS were shown during the presentation
🔗 ABOUT GTBOP
Getting the Best of Pests (GTBOP) is a continuing education webinar series for pest management and Green Industry professionals, hosted by the University of Georgia Center for Urban Agriculture.
