Investigation of hybrid Freeman maple resistance to Chrysobothris flatheaded borers (Coleoptera: Buprestidae)

Red maples (Acer rubrum L.; Sapindales: Sapindaceae) are common shade trees well known for their stunning autumn foliage and fast growth. They are a popular choice for landscapes, parks, and public places across the United States. Flatheaded borer species in the genus Chrysobothris (Coleoptera: Buprestidae) are some of the most damaging insects in red maple production, with attacks being most common on stressed and newly transplanted trees. In nurseries, red maples routinely experience flatheaded borer attacks, while the Freeman maple hybrid 'Autumn Blaze' has been reported as potentially resistant to flatheaded borers. In this study, traits of three borer susceptible red maple cultivars ('Brandywine', 'Sun Valley', and 'October Glory') were compared against a potentially resistant Freeman maple hybrid cultivar for baseline differences as well as differences under the stress of a foliar herbicide application Scythe (pelargonic acid 57%). Morphological, physiological, and biochemical traits of the red maple cultivars were evaluated and contrasted with the hybrid to identify traits related with borer resistance. Under normal conditions, the hybrid maple exhibited faster growth, greater concentrations of sulfur, and lower concentrations of zinc and flavonoids in leaf tissues compared to red maples. The herbicide stress treatment resulted in greater nitrogen and sulfur concentrations in hybrid foliage, but less chlorophyll, flavonoid, and zinc concentrations compared to the red maple cultivars. Field trials validated borer preference for red maples over the hybrid. Traits associated with the hybrid warrant additional study if an understanding of the causal relationship with borer resistance is to be achieved.