1979 – 1982: Geraldton Spray Drift. Pesticide of concern: 2,4-D

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Airborne 2,4-D and tomato damage at Geraldton (Gilbey et al 1984).

A series of studies were conducted between 1979 and 1982 to monitor the airborne levels of 2,4-D in the Geraldton region. The work was coordinated by Des Gilbey, Weed Research Officer, assisted by a team of officers from several government departments.

The work was done in response to complaints over many years that tomato growers in and around Geraldton were suffering crop damage as a result of 2,4-D spray drift caused by wheat growers further east. It was originally assumed that volatile 2,4-D ester vapour from several kilometres away was responsible. This may or may not have been so, but the monitoring study coincided with a change in Restricted Spraying Regulations, when the use of high volatile 2,4-D esters was prohibited within 50km of Geraldton, instead of the 19km permitted before 1979.

The study showed that tomato crop damage was more likely to have been caused by short distance droplet drift of 2,4-D amine (which is allowed to be used within 50 km of Geraldton), and to a lesser extent droplet and vapour from 2,4-D ester applied within the prohibited area.

This study has implications for the problem of herbicide drift and damage to non-target vegetation. The study found that, with the monitoring equipment and resources available it was not possible to identify individual spraying events – and thereby pin-point the source. Neither could the monitors distinguish between a high concentration for a short time, and a constant low level during the weekly monitoring interval. Short duration, say hourly, monitoring would be needed to detect peak concentrations.

p35 Monitoring Pesticides. A Review to the Environment Protection Authority by Peter A Rutherford December 1989