The possible loss of registration for the insecticide chlorpyrifos (Lorsban) has become a looming concern for the tree fruit industry for the up-coming season. The EPA will be asking for public comment on this insecticide over the next few weeks. Its likely that very strong public support will be required for the registration of chlorpyrifos to be retained.
For apple growers the use of chlorpyrifos has provided a unique mode of action for resistance management specifically to maintain control of obliquebanded leafroller, San Jose scale and dogwood borer (DWB). It has also been shown in preliminary studies to have efficacy for managing the black stem borer (BSB), a forest insect pest in the ambrosia beetle family that moves into young trees under stress from environmental, disease or other insects.
The mechanisms for effective management of BSB in young trees includes providing ample soil moisture during the growing season and providing effective disease and insect pest management including trunk borer management for DWB to reduce loss of trunk cambium. However, in years of excessive water from prolonged rainfall, trees can experience severe stress, producing ethanol as a bi-product, which the black stem borer uses to find a susceptible host. To inhibit BSB from entering the trunk of the stressed tree, a long residual insecticide applied to the tree trunk during adult emergence, such as chlorpyrifos, is critical under these conditions to keep the insect from entering the tree. Once the beetle enters the tree there is little to be done to limit the impact of the beetle.
Both DWB and the BSB have been attributed to the rapid tree decline and death of hundreds of apple trees in dwarfing high-density plantings throughout NY. Although there may be alternatives to chlorpyrifos for DWB management, there seem to be few effective alternatives for black stem borer.
If you see the retention of chlorpyrifos in the pest management toolbox as an important tool to manage the insect pest complex while providing a effective component for use in Integrated Resistance Management programs, a petition is now available to let EPA know your opinion. You can fill in the form on-line to the EPA to request chlorpyrifos registration be continued for use in apple production.