Evaluation of a trailer spray unit with boom and boomless nozzle system for woody weed control.  P. C. Fagg, A. D. Manderson, A. A. Pook and G. J. Cameron.  January 1987.  17pp. (unpubl.)

SUMMARY

A GOLDACRES tractor-drawn trailer spray unit was evaluated for application of LONTREL herbicide (active constituent-clopyralid 300 g L^-1) for the control of silver wattle in a two year-old radiata pine plantation in the North East Region. Two types of nozzle systems (conventional boom and boomless type) were tested in combination with two rates of herbicide mixture volume (nominally 150 L ha^-1 and 300 L ha^-1) in June 1983. Defoliation and mortality of silver wattle was assessed at 5 and 14 months after treatment and the operational and mechanical efficiency of the spray unit was evaluated.

In terms of percentage of silver wattle stems either dead or severely defoliated 14 months after treatment, there was (i) no significant difference between the two nozzle systems (even though 25% less LONTREL was applied in the boomless nozzle treatments), and (ii) significantly better control with the lower volume rate. These results reversed the trends apparent at 5 months. Possible reasons for this are discussed.

The rate of coverage when the unit was fitted with the boomless nozzle was 3.6 to 4.8 ha h^-1 (tractor travelling every third or fourth row) compared with only 2.4 ha h^-1 with the conventional boom (every second row). This made a cheaper total treatment cost for the boomless system of $224 to 230 ha^-1 compared with $241 ha^-1 for the conventional boom. The boomless system had the additional advantage of not being obstructed by tall pines or woody weeds and was able to project some spray into windrows.

The cost of this type of ground treatment was comparable with aerial spraying (approx. $240 ha^-1) for an assumed weed population of 2500 stems ha^-1. However, ground-based treatment (trailer spray unit plus manual) would be up to 30 times slower than aerial spraying (eg. for a 300 ha plantation, the respective treatment times were estimated to be 63.3 and 2.1 days).

Further evaluation of the trailer spray unit is necessary. However, this initial test showed that the unit has the capability to treat, in a cost-effective manner, low-to medium-density woody weed populations in radiata pine plantations on slight to moderate slopes free of ground debris. For relatively advanced woody weed growth, a boomless spray system operating along every third row of pine is recommended.