Evaluation of Beacon® herbicide for the release of messmate seedlings from bracken competition.  G. H. Pritchard.  June 2005.  22pp. (unpubl.)

SUMMARY

Naturally regenerating eucalypt seedlings in previously logged areas can suffer severe competition from bracken fern (Pteridium esculentum). At present there is no registered herbicide to selectively control bracken fern in this situation. The herbicide primisulfuron methyl (Trade name "Beacon") was thought to have some promise in this situation, and a trial was set up in the Mt Lonarch State Forest in Western Victoria to evaluate this herbicide in comparison with two other chemicals registered for bracken control.

In April and October 2000, single applications of primisulfuron methyl at 56 g, 75 g, 112 g and 150 g ha^-1 were sprayed on bracken overtopping messmate (Eucalyptus obliqua) seedlings. Six months after the April application there were no new fronds with any rate of primisulfuron methyl, but there was no significant death of old fronds and little noticeable reduction in bracken ground cover. By 12 months after application an estimated 36 to 60% of bracken foliage, depending on primisulfuron methyl rate, was dead and the density of healthy fronds was reduced to means of 3.8 to 9.3 m^-2 compared with 14.0 m^-2 on untreated plots. At 18 months after application, control (estimated visually) was 64-73%, but many small new fronds were present and by 24 months after application there was no significant control with any rate.

The October application of primisulfuron methyl resulted in foliage death of bracken of 43 to 53% after 6 months while healthy fronds had declined to 3.8 to 7.7 m^-2 compared with 14.0 m^-2 on untreated plots. At 12 months control was rated at 73-94% and frond density was 6.1 to 12.8 m^-2 compared with 22.4 m^-2 on untreated plots, but by 18 months after application no rate gave significant control of bracken.

All rates of primisulfuron methyl at both application times caused significant (p=0.05) initial damage to messmate seedlings although, depending on rate and application time, 80-92% of plants survived 12 months after application. At all assessments up to 24 months after the April applications and 18 months after the October applications, messmate growth (as measured by change in volume index) was either less than, or no greater than, the untreated control.

Application in April 2000 of asulam at 4.8 kg ha^-1 plus Pulse 0.2% v/v gave significantly better bracken control than primisulfuron methyl treatments at most assessments, while asulam at 4.8 kg ha^-1 plus Ulvapron 2% v/v and metsulfuron methyl at 36 g ha^-1 gave comparable control to primisulfuron methyl. However these three treatments killed 54, 56 and 87% of messmate seedlings respectively.

Bracken control with metsulfuron methyl was less than expected and it is possible that the factors that contributed to this result also would have affected the applications of primisulfuron methyl made at the same time.

It was concluded that, in this trial, primisulfuron methyl, applied in either October or April at rates 56-150 g ha^-1, was not an effective treatment to selectively release messmate seedlings from bracken fern.