Evaluation of Roundup^®, Tordon TCH^® and Velpar L^® herbicides for the control of eucalypt regrowth in softwood plantations by stem injection.  P. C. Fagg, G. Hepworth, W. G. Smith and G. J. Cameron.  January 1990.  17pp. (unpubl.)

SUMMARY

The efficacies of the three herbicides, ROUNDUP (active constituent-glyphosate), TORDON TCH (triclopyr + picloram), and VELPAR L (hexazinone), which are all registered for eucalypt control, were tested and compared using the stem-injection technique.

Eucalypt regrowth of four species broad-leaved peppermint (Eucalyptus dives), narrow-leaved peppermint (E. radiata ssp. radiata), manna gum (E. viminalis) and brittle gum (E. mannifera) in a 4 year-old radiata pine (Pinus radiata) plantation in north-eastern Victoria were studied in the trial, which covered injections (using a basal spear) in three seasons (spring, autumn, and winter) and two sites (upper and lower slopes).

The study showed that all species could generally be satisfactorily controlled ( > 90% trees dead or severely defoliated) by stem injection with either ROUNDUP or TORDON TCH at the recommended (1989) label rates, or VELPAR L at half the label rate. TORDON TCH was the most cost-effective herbicide.

Regrowth on the upper slopes (harsher sites) was more difficult to control than that on lower slopes. On the upper slopes, the efficacy of the herbicides varied with season with poor results following injection in spring. On the lower slopes, autumn and winter injections were also preferable, although on these less harsh sites the treatment effects did not vary greatly with season.

With the herbicides and rates examined, there was no evidence of 'flashback' (herbicide transfer via root grafting) to adjacent pine trees.

The minimum effective dosage of glyphosate expressed as active constituent per unit basal area (g/m2) was of the same order as those reported for other eucalypt species, though it is apparent that different species have different threshold levels of susceptibility.