Frederick G. Burton

A controlled-release herbicide device for multiple-year control of roots at waste burial sites

Abstract Based on the available data, a trifluralin-releasing device was developed with an effective lifetime of approximately 100 years. Herbicide released from the device in soil will prevent root penetration through the soil layer without harming the overlying vegetation. Equilibrium concentrations of trifluralin in soil can be adjusted (together with the theoretical life of the device) to suit specific needs. Based on early results of the field trials, concentrations of trifluralin sufficient to prevent root elongation were maintained in the soil, with minimal diffusion out of the immediate area.

SLOW-RELEASE RADIOISOTOPE IMPLANTS AS INDIVIDUAL MARKERS FOR CARNIVORES

We developed a technique that identifies an individual animal by labeling its excreta. Various gamma-emitting radioisotopes were incorporated into implantable discs made of polylactic acid (PLA), a biodegradable polymer. Laboratory testing and field studies with coyotes (Canis latrans) demonstrated that the 6 radioisotopes evaluated were released from the subcutaneously-implanted polymer at a relatively constant rate after an initial burst phase and allowed a minimum marking period of 6 months. Prototype slow-release implants were used in a field study of coyotes to estimate population abundance, estimate home range, assess individual diets, and examine social and scent-marking behavior. The implant technique has potential widespread application in studies of wild carnivores.

Field validation and performance specifications of a long-term controlled-release herbicide delivery system for multiple-year control of root growth

Abstract A trifluralin-releasing polymeric device to control root growth (i.e., a biobarrier), with an estimated bioactive lifetime at 13° C of approximately 100 years, has been undergoing field tests for more than 7 years. To evaluate the biobarrier performance, including the change in herbicide content of the device as well as changes in the herbicide soil profile concentrations over an extended period of time, subplots of the field test plots were excavated, the trifluralin-releasing devices were retrieved, and soil samples were taken over a 7-year period following initiation of the field tests. Due to a less than expected soil overburden and a lack of soil moisture at the site, the average temperature at the level,of the devices is significantly greater than 13°C. Based on the results of the final field sampling, (1) an estimate of the bioactive lifetime of the biobarrier controlled-release system remains close to the lifetime predicted when the devices were first laid down, being controlled only by the average annual temperature of the controlled-release devices at the site; and (2) the vertical profile of trifluralin in the soil appears to stabilize within a few months of placement of the biobarrier devices, with diffusion of trifluralin from the site not being detectable. The results of these field validation tests indicate that the device is truly a long-term controlled-release device that continues to function as originally predicted. Initial field results for trifluralin controlled-release devices bonded onto a geotextile for ease of application are described.