Grain growers embarking on sowing this year's winter crops are advised to factor the soil persistence of herbicides into their programs.

Weed specialist Mark Congreve, of Independent Consultants Australia Network (ICAN), says it is important to understand the soil persistence of a herbicide and its potential impact on following crops in the rotation, prior to the herbicide's use.

Herbicide behaviour

"Herbicides designed for residual weed control need to provide weeks or months of persistence in the soil to achieve their desired weed control objectives," Mr Congreve says.

"As well, some herbicides that typically are used for post-emergent weed control and which are not typically considered 'residual' herbicides may also persist in the soil for some time after application."

New resource

To provide grain growers and advisers with relevant information to assist in planning the use of herbicides in crop sequences and in managing rotation constraints, the GRDC has produced a national reference manual called 'Rotational Crop Constraints For Herbicides Used In Australian Farming Systems'.

It is divided into two parts.

The first part covers the principles of herbicide persistence in the soil and the factors that influence herbicide breakdown.

"Understanding these factors may help to predict variability from year-to-year under different environmental conditions, to assist decision making in situations where labelled plant-back requirements have only just been met - or where statements on the herbicide label do not adequately cover the paddock situation," Mr Congreve says.

Part two of the manual is a summary of label statements relating to directions for managing rotational crops.

The manual contains a series of frequently asked questions and links to other useful resources.

GRDC Research Code: ICN1811-001SAX

More Information: Mark Congreve, ICAN, 02 9482 4930, 0427 209234