Weeds - Phase 1 - Research Highlights

Weeds on fence-lines and roadsides

What the report is about

Roadsides and fence-line areas throughout Australian agricultural regions are typically poorly managed and provide sites for the incursion of weeds into adjoining agricultural land. The weed species present are observed to be the same as those that dominate the farming landscapes and potentially act as both a sink and a source for herbicide-resistant genes.

The aim of this project was to identify weed species and biotypes that pose the greatest threats to production agriculture if incursion and dispersal were allowed to occur from roadside and fence-line areas into farming zones.

Methods used

A random survey was carried out in order to gain information on the occurrence and distribution of weed species and biotypes along roadsides and fence lines throughout the southern Mallee region of Victoria. The region surveyed was a square area bounded by Sea Lake to the north, Birchip to the south, Hopetoun to the west and Lalbert to the east.

Dominant weed species present at the time of sampling were counted on either side of the fence (road side and paddock side). Seed bank levels and herbicide resistance status were determined for the species and biotypes collected.

Results/key findings

The inspection carried out during June to August led to the identification of more than 20 visible weed species. The most dominant were annual ryegrass and barley grass; they were present at 45 per cent of surveyed sites. The other two dominant weed species were hedge mustard and brome grass. There appeared to be little difference between the dominant species found on the road and paddock sides of the fence.

From seed bank surveys, barley grass was the most dominant species that germinated, indicating there was a significant seed bank in the soil samples collected. Ryegrass was found at a lower seed bank level in comparison with barley grass, despite being present in the same plant density, as measured during the season.

Of the samples collected from the roadside and paddock side of cropping paddock fence lines and tested for herbicide resistance, only one - an annual ryegrass population - was found to exhibit resistance to sulfometuron. No resistance to glyphosate or 2,4-D was found. These results suggest that the incidence of weed species with herbicide resistance along fence lines in Victoria's southern Mallee is low.

Implications for relevant stakeholders

The survey allowed assessment of the level of resistance in the paddocks, which provides valuable information for determining the best management practices for fence-line weed control. By demonstrating that fence-line weeds can pose the same threat as those found in a paddock, the results show that controlling these weeds is important

Fence-line weed control should be part of integrated weed management in order to avoid the onset of herbicide resistance, especially resistance to glyphosate.

Recommendations

Although the level of herbicide resistance was found to be low in this survey, repeated use of herbicides from the same group would probably lead to resistance to those herbicides. The potential risk of in-paddock weeds developing glyphosate resistance has significant implications for farmers in the short, medium and long term.

The results of this survey can be used to increase growers' awareness and promote action to concentrate on controlling the dominant weed species (ryegrass and barley grass) found along fence lines. The best strategies will be the same as those used in paddocks-for example, timely control of weeds and rotational use of herbicides with different modes of action.