A SWING to disc seeders and no-till cropping is bringing residual herbicide issues to the surface.
Involving sowing crops into standing stubble, no-till adoption has jumped from 10 to 80 per cent in southern NSW over the past decade.
In the past, residual herbicides were sprayed on cultivated paddocks and cross-worked.
Now they are either added to a knockdown herbicide and incorporated by sowing, or applied after sowing.
But many herbicides were made for traditional farming systems and labels have not kept pace.
NSW Department of Industry and Investment agronomist Barry Haskins said some herbicides did not mention disc machines on their labels.
"There are too many assumptions that farmers understand how to use residual herbicides and how each one works," Mr Haskins said.
Trials have been run in southern NSW from 2007 to last year to gather data to support herbicide permit applications or label changes.
Mr Haskins, of Griffith, said the trials found residual herbicides at sowing were effective at controlling weeds in-crop and well into the next summer.
"Knowing the chemistry and mode of action of each herbicide is paramount for crop safety and weed control," he said.
"Incorporated by sowing techniques seem to be the safest way of using most residual herbicides, as the seed furrow is left free of high levels of herbicide.
"Because of the furrow created by most no-till seeders, post sowing pre-emergent herbicide applications are not ideal and are usually not supported by labels.
Mr Haskins said there were no rules of thumb for sowing speed, row spacing and soil throw.
"Machines must be checked in each paddock," he said.
"Disc angle, numbers, disc size and shape, sowing speed, closer plates and press wheels on disc machines will have an effect on soil throw."
The trials also revealed knife points and harrows caused herbicide-treated soil to return into the soil furrow.
"High stubble loads and pre-emergent herbicides can work together: always spray in the same direction as last year's stubble row," Mr Haskins said.
