Quick Dips

Computerised Spraying

A computer model of aerial spraying of herbicides is providing valuable efficiency and safety guidelines for forest managers. It was originally developed by the US Forest Service and Army for insecticide use, but the Forest Research Institute has been using it for herbicide applications.

"When we got the model, there'd been very little done with herbicide usage," says FRI scientist Dr Brian Richardson.

Adaptations were made for the difference in application techniques. With herbicides, the droplets are much larger to prevent spray drift. The model has shown that using nozzles which produce a minimum number of droplets less than 150 microns in diameter helps reduce the chance of drift.

Other drift-related recommendations include flying no higher than 10 metres, keeping an eye on humidity and temperature, and using a spray boom which is less than 80% of the rotor diameter or wingspan. While strong winds will affect spray settlement, low winds have also been found to cause problems because of their uncertain variabililty.

One of the most valuable uses Richardson sees for the model is in providing defined limits for specific spraying operations and applications. Running a variety of simulations shows both managers and pilots the most appropriate conditions for spraying and the sorts of strategies to use.

"I was really astonished at how well the model performed given the amount of variables involved and how they interact," Richardson says.