PENETRATION AND PERMANENCE OF WOOD TREATMENT INSECTICIDES IN STRUCTURAL SOFTWOODS .1. CHLORPYRIFOS

Rough-surfaced versus smooth-surfaced wood has a significant effect on uptake and absorption of chlorpyrifos (Dursban(R) TC), with rough surfaces tending to absorb liquid more readily. The effect of wood surface orientation may or may not have a significant effect at reducing penetration of liquid insecticides, excluding the possibility of direct runoff or dripping of the liquid. Penetration of chlorpyrifos after 24 hours is significantly greater in southern yellow pine than in northern hard pine, spruce, or fir. Initial surface concentrations, vulnerable to volatile loss over time, are lower in southern yellow pine; whereas concentrations below the surface remain more stable for up to 52 months. Initial high surface concentrations of less permeable woods, i. e. northern hard pine, spruce and fir, are also lost by volatilization or chemical breakdown. Below-surface concentrations in these woods generally start out at a low level and remain low after six months. Two aspects of the biology of Hylotrupes bajulus are considered when selecting a surface application of an emulsion formulation of insecticide for treatment of limited infestations. Because pine is a preferred food for H. bajulus larvae, and because infestations are frequently not discovered until larvae are two to three years old, remedial treatment of pine with a surface-applied emulsion formulation of chlorpyrifos can remain effective until adult emergence. Treatment of less permeable types of wood indicate an effective control period of much shorter duration.