Weeds: what you do is what you get

With the wider adoption of conservation farming practices, producers need to be aware that different farming systems promote different weeds. These research results are from southern NSW but the message applies to other grains regions

One aspect of the long-term Stable Agriculture through Wheat and Good Legumes (SATWAGL) trial, at the Wagga Wagga Agricultural Institute, is the assessment of weed infestations under different farming systems.

Scientists have been studying the growth of several grass and broad-leaf weeds since the trial began in 1979.

The research, which is partly supported by growers and the Federal Government through the GRDC, shows that some weeds grow better with cultivation.

"Fumitory, for example, increases in presence with an increasing number of tillage passes," said NSW Agriculture research scientist Damian Heenan.

In 1994, under a no-till system (stubble retained), 5 per cent ground cover of fumitory was recorded. However, three tillage passes (stubble retained) led to an infestation of 40 per cent ground cover.

"There was also a suggestion that burning stubble slightly promoted fumitory growth with the highest ground cover, 50 per cent, recorded after three tillage passes with stubble burnt.

"In 1981, before our successes of controlling wireweed with herbicides, cultivation and stubble burning led to an infestation of 52 per cent ground cover compared with less than 1 per cent under no-till with stubble retention," Dr Heenan said.

On the other hand

Alternatively, giant brome grass prefers conservation farming practices — no-till and stubble retention — according to three years of trials in wheat-lupin rotations.

"In 1986, no-till with stubble retention led to a 60 per cent ground cover of brome grass while three tillage passes and stubble burnt led to an infestation of just 10 per cent.

"The fact that deep incorporation of seed reduces the germination of brome grass explains why the weed favoured no-till practices.

Weed study results from the same trial also show that vulpia (silver grass) fell off when lime was applied.

Dr Heenan said: "this is more likely to be related to greater competition, provided by the better growth of wheat, rather than a direct effect of pH or lime on vulpia growth".

Program 3.5.2 Contact: Dr Damian Heenan 02 6938 1857, Mr Bill McGhie 02 6938 1801

Region North, South, West