What moves through the trunk can move to the tap
Sweet sap seasons are sacred in the sugarbush. Yet a speckled sapsucker is stirring stress among syrup producers.
The spotted lanternfly (SLF), first detected in Pennsylvania in 2014, has spread swiftly and is now established in at least 19 other states. This invasive Asian planthopper prefers tree-of-heaven, a sun-loving invasive that colonizes disturbed sites. Still, it readily feeds on native trees including red maple and sugar maple.
High densities of SLF have been observed feeding on maples in heavily infested states in warmer months. Feeding reduces tree vigor, although widespread dieback or mortality has not been reported. Even so, producers worry about subtle setbacks. Sap volume may decline. Sugar content may shift. Syrup yield and quality may suffer.
Cover sprays of broad spectrum insecticides such as pyrethroids can control SLF, but spraying large trees across forested acreage is rarely practical. That reality prompted researchers in the Departments of Entomology and Forestry at Michigan State University to test systemic options. Could maples be treated during the growing season to protect against SLF and other pests without contaminating sap or syrup?
In a field trial, mature red maple and sugar maple trees were treated with imidacloprid or dinotefuran, timed to target late instar nymphs and adults. Researchers then quantified insecticide residues in foliage, sap and syrup.
The leaves revealed early patterns. Dinotefuran residues were about 70% higher in red maple foliage than in sugar maple foliage, though differences were not statistically significant due to variability. Species-specific uptake may influence how systemic products move within trees.
Sap sampling showed consistent trends. Dinotefuran concentrations were higher in sugar maple sap than in red maple sap across collections, though differences were not significant. Imidacloprid residues were also consistently higher in sugar maple sap than in red maple sap. What moves through the trunk can move to the tap.
The most critical concern centered on syrup though. As sap was boiled and evaporated, both dinotefuran and imidacloprid residues became concentrated. Dinotefuran measured 0.19 parts per million in sugar maple syrup and 0.23 ppm in red maple syrup. Imidacloprid measured 0.12 ppm in sugar maple syrup and 0.08 parts ppm in red maple syrup.
These findings highlight a careful calculus. Systemic insecticides can protect trees where spraying is impractical, yet residues can persist into finished syrup. As SLF continues its spread – and as other threats such as Asian longhorn beetle loom – producers and regulators must weigh tree health, pest pressure and product purity together.
In the sugarbush, smart science and steady stewardship will shape the path forward.
by Enrico Villamaino
