What are the water quality implications of treating hemlocks growing near streams?
Imidacloprid is inert once it binds to organic matter in the soil, at which point it will move only 9 to 14 inches. However, care must be taken since imidacloprid can flow across the surface of the soil if heavy rains occur soon after treatment. Several studies of hydrologic impact after imidacloprid treatment have shown no imidacloprid in streams. The only documented impacts of imidacloprid on stream life are effects on Daphnia, an extremely sensitive stream microorganism which can be wiped out by flash floods and other natural events but which usually recolonizes streams to its former levels within a couple of weeks. Managers use care around water, but are willing to treat hemlocks on the creek bank as long as the imidacloprid is injected into the soil on the non-creek side of the tree. When should hemlocks be treated with imidacloprid? The treatment window for soil treatment is fall and spring. The soil must be moist but the hemlock tree should not be dormant. In this area, hemlocks
