First Report of Beech Bark Disease in Michigan

Area of Science:

• Plant Pathology
• Forest Entomology
• Ecology

Background:

• Beech bark disease is a significant threat to American beech (Fagus grandifolia) forests.
• The disease results from the synergistic interaction between the introduced scale insect (Cryptococcus fagisuga) and native or introduced fungi (Nectria galligena, N. coccinea var. faginata).
• Previous records indicated the beech scale's presence in Ohio and Ontario, but its status in Michigan was unknown.

Purpose of the Study:

• To document the first occurrence and distribution of beech scale and beech bark disease in Michigan.
• To identify the fungal pathogens associated with the disease in the surveyed areas.
• To establish baseline data for future monitoring and management strategies.

Main Methods:

• Field surveys were conducted in the Upper Peninsula (UP) and Lower Peninsula (LP) of Michigan to locate beech scale infestations.
• Samples of beech bark and associated fungi were collected from infested stands.
• Fungal identification was confirmed through morphological analysis of perithecia and ascospore characteristics.

Main Results:

• Beech scale (Cryptococcus fagisuga) has established populations in multiple counties across both the LP and UP of Michigan.
• The fungal pathogens Nectria galligena and Nectria coccinea var. faginata were identified in association with scale insect infestations.
• The distribution suggests the insect has been present for years, potentially introduced and spread via human activity in recreational areas.

Conclusions:

• This study confirms the presence of beech scale and beech bark disease in Michigan, marking a new invasive range for the pest.
• Nectria galligena and Nectria coccinea var. faginata are the identified causal agents of the disease in the state.
• Further surveys are planned to fully delineate the extent of the infestation and pathogen distribution.