Crews are treating trees that host spotted lanternflies in watershed property owned by the Bethlehem Authority this week. The treatments should destroy about 274 Trees of Heaven (Ailanthus trees), hopefully stopping the spread of the pest on this land.

Last September, the Bethlehem Water Authority first discovered spotted lanternflies on the lower watershed property, which spans 12,500 acres in Carbon and Monroe counties, according to Executive Director Stephen Repasch. This was one of the first lanternfly sightings in Monroe county, and the water authority immediately reported it to the United States Department of Agriculture.

Over the next months, the USDA sent out crews to survey the property. The crews discovered more than 200 host trees concentrated in a 1,000-acre area, Repasch said.

The USDA hired Buchanan Consulting Services to treat the trees.

The contractor is spraying the base of smaller trees with herbicides Pathfinder II and Capstone, and larger trees with the insecticide Transtect.

The leaves absorb these sprays and then the lanternflies eat the leaves, which kills the flies and eventually the trees.

“These are invasive trees anyway. They really don’t belong in the watershed,” Repasch said.

The herbicides and insecticide are approved by the U.S. Environmental Protection Agency and the Pennsylvania Department of Environmental Protection. They are also not prohibited by the Forest Stewardship Council.

“The FSC is our Bible,” Repasch said. “We can’t do anything — we wouldn’t do anything — that is outside the bounds of the FSC.”

The crews treated about half the trees on Tuesday and will finish Wednesday or Thursday, depending on the weather, Repasch said.

The spotted lanternfly, a bug native to Asia, was first discovered in Berks County in 2014. This pest damages trees by sucking tree sap and excreting honeydew that can cause black mold. The bug has now spread to 14 counties in southeastern Pennsylvania.