Developing a Media Moisture Threshold for Nurseries to Reduce Tree Stress and Ambrosia Beetle Attacks

Area of Science:

• Horticulture
• Entomology
• Plant Pathology

Background:

• Exotic ambrosia beetles are significant nursery pests, attracted to ethanol emitted by flood-stressed trees.
• Current management relies on insecticides, highlighting the need for alternative integrated pest management (IPM) strategies.
• Understanding tree stress responses is crucial for developing effective pest control methods.

Purpose of the Study:

• To establish a media moisture threshold for integrated pest management (IPM) of ambrosia beetles.
• To assess nursery grower practices contributing to ambrosia beetle infestations.
• To identify optimal irrigation management for preventing pest attacks.

Main Methods:

• Comparing ambrosia beetle attacks on flooded versus unflooded Cornus florida, Cornus kousa, and Magnolia grandiflora.
• Growing flood-tolerant Acer rubrum and flood-intolerant C. florida at various media moisture levels (10-90%).
• Monitoring commercial nursery media moisture during peak ambrosia beetle flight periods.

Main Results:

• Flooded C. florida, C. kousa, and M. grandiflora experienced significantly more attacks than unflooded controls.
• Flood-intolerant C. florida at 70-90% media moisture were attacked and died; trees at 30-50% moisture were unattacked.
• Flood-tolerant A. rubrum showed no attacks regardless of flooding or moisture levels.
• Commercial nurseries frequently exceeded the identified 50% moisture threshold during peak pest activity.

Conclusions:

• An upper media moisture threshold of 50% is recommended for growing flood-intolerant trees like C. florida.
• Implementing this IPM tactic can reduce ambrosia beetle damage and reliance on insecticides.
• Further research into substrate and irrigation adjustments is needed to help growers meet this threshold.