Field trial to test methods for eradication of fennel (Foeniculum vulgare Miller) on roadsides of Kangaroo Island, South Australia

Philip Pisanu and Trish Mooney, Department for Environment and Heritage, Kingscote, South Australia 5223, Australia.


The perennial herb fennel (Foeniculum vulgare Miller) has been present on Kangaroo Island for approximately 50 years but has increased its range substantially in recent decades. Fennel currently infests a 7 km long section of roadside and an area of approximately 400 ha of adjacent rural lands. In 2005-06 a field trial was conducted to test a number of herbicide treatments for fennel management. The trial used glyphosate (Glyphosate 360) and triclopyr (Garlon 600) and different combinations of slashing. Pre-chemical treatment of trial plots was carried out in June 2005, chemical treatments were applied in late September 2005, and three subsequent assessments of the trial were undertaken in October 2005, February 2006 and October 2006.

In October 2005 more than half of chemically treated plants were dead or in poor condition, while fennel in untreated control plots remained unchanged. Slashing of plots prior to herbicide application resulted in 20% higher mortality rates in glyphosate treatments but no significant differences in mortality were recorded in slashed triclopyr plots. By February 2006, fennel plant mortality had increased overall in chemical treatments but only one plant died in controls. Glyphosate only treatments had significantly lower mortality than triclopyr only, triclopyr and slashing, and glyphosate and slashing treatments. Overall, slashing was more effective for glyphosate treatments than triclopyr treatments, resulting in a mortality rate 20% higher than the unslashed glyphosate treatment, whereas the difference between slashed and un-slashed triclopyr treatments was only 1.3%. Glyphosate only treatments had significantly higher resprouting rates (23%) than other treatments. Seedling emergence was observed in three glyphosate plots but not in triclopyr treatments.

In October 2006 post-treatment regeneration from resprouting and seedling germination in glyphosate treatments was significantly higher than regeneration rates in triclopyr treatments, where the response was equivalent to that in untreated controls. Few seedlings emerged in either controls or chemically treated plots over the study period, but this may have been influenced by below average rainfall in winter/spring 2006. We recommend triclopyr as the preferred chemical for fennel control on Kangaroo Island because of higher plant mortality and less post-treatment resprouting from basal corms. Fennel control should include at least two annual cycles because it is likely that some survival of herbicide treated plants will occur (resprouting) and/or seedlings will emerge. Few native plants were found adjacent to dense fennel infestations and recent surveys indicate that mostly exotic grass species are invading herbicide treated plots. Future management of treated areas will probably require restoration of native species, and other forms of intervention such as prescribed burning may prove beneficial.

Keywords: Fennel, (Foeniculum vulgare), herbicide field trial.


Plant Protection Quarterly (2008) 23 (3) 127-130.