Silver wattle control in pine plantations with Lontrel and Roundup applied with a tractor-mounted rope-wick applicator.  P. C. Fagg, G. J. Cameron and D. W. Flinn.  February 1987.  15pp. (unpubl.)

SUMMARY

This report describes a field study that evaluated the SHERWOOD MR-1 rope-wick applicator (a 3.1 m wide, tractor-mounted, multi-rope unit) for the control of silver wattle (Acacia dealbata) in a young radiata pine (Pinus radiata) plantation, as an alternative to ground or aerial spraying methods. The herbicides LONTREL (clopyralid) and ROUNDUP (glyphosate) were separately applied with and without the adjuvant oil ULVAPRON, using one and two passes of the rope-wick applicator.

On the basis of the proportion of tagged silver wattle stems in the 76-100% defoliated or dead categories eight months after treatment, LONTREL gave significantly better (P < 0.05) control than ROUNDUP for either one (79% vs 35%) or two (81% vs 59%) passes of the rope-wick. The small improvement in control by the addition of ULVAPRON to LONTREL (one-pass) was not significant at the 5% level. ROUNDUP caused minor damage to the tips of up to 20% of pines, despite care being taken to avoid wiping them; LONTREL on the other hand caused no damage to the crop plant.

Total cost per hectare of treating an 'average' plantation in north-eastern Victoria, including the cost of manually treating areas which are inaccessible to the rope-wick, was estimated at $182 ha^-1 for a one-pass treatment using 1.7 L ha^-1 LONTREL. Although this cost assumed a relatively low density of silver wattle (2500 stems ha^-1), the total cost compares very favourably with an estimated $242 ha ^-1 for aerial and $230 ha^-1 for ground spraying of a similar area. However, costs of rope-wick application followed by manual stem injection would exceed those of spraying methods in areas with dense wattle populations, and the technique is unsuited to sites with steep topography or with significant ground debris.

The rope-wick applicator proved to be effective and durable, though front-mounting rather than rear-mounting, and an increase in rope angle would have improved the wiped area of foliage and stems. The rather slow rate of coverage (0.5 ha h^-1) achieved by the small crawler tractor used in the study could be improved by using a large, 4-wheel-drive tractor. These improvements should be tested in future trials.

On sites with mild topography that are free of substantial ground debris, the rope-wick technique offers a cost-effective alternative to aerial spraying for control of relatively low densities of silver wattle in pine plantations, particularly where spray drift should be completely avoided, or in small areas which do not justify aerial treatment.