One front on the weed war by Alex Nicol

Gauging the value of stubble in suppressing weed growth.

Focus is swinging back to stubble retention in an integrated approach to weed control, as the problem of herbicide-resistant weeds grows. The question is, how much stubble retention?

At the Agricultural Research Institute in Wagga Wagga, NSW, a newly planned major trial will compare a range of cultivation options over a four-year cycle. Sown on country not cultivated for seven years and with populations of resistant rye and wild radish, it promises a truly commercial look at the problem.

“By comparing stubble burning and stubble retention in both the wide and narrow sowing configurations, we hope to get a gauge of the value of stubble in suppressing weed growth,” said agronomist Steve Sutherland.

Vigorous crop best defence

“It’s an article of faith that the best defence against weeds is a vigorous crop and we know that when the seedbed is cultivated in the traditional fashion, early crop vigour is a casualty under wide row spacing. We’ll be trying to find out whether, by retaining stubble, we can compensate for this, and we’ll also be testing the impact of using less herbicide.

“We can’t continue with a farming system that depends heavily on herbicides, that’s black and white,” says Mr Sutherland, “and a system of stubble retention and minimum tillage depends on having effective herbicides.

“The last thing you need when you have a resistance problem is increased herbicide use, so we’ll be incorporating stubble burning in the trial and gauging the impact of using minimal amounts of herbicide as well as ‘throwing the lot’ at it.”

Four-year rotation

The trial will extend over four years with a rotation involving wheat, canola, lupins and a pasture phase. Mr Sutherland expects that some of the plots will get very dirty and that the existing radish in the paddock will be difficult to control especially in the low herbicide plots.

“But that's the sort of test farmers in the area are facing,” he says. He anticipates that the four-year period will see a change in the structure of the weed population, with annual weeds giving way to perennial weeds under some treatments. “Brome grass could emerge as a problem.”

Mr Sutherland said it may well be that new sowing and cultivation equipment will be judged in any cost-benefit analysis of the system’s ability to control weeds.

Contact: Mr Steve Sutherland 02 6938 1955