With sorghum planting about to kick off in earnest, northern-region growers need to apply a seed safener to prevent plant damage when using metolachlor-based pre-emergent herbicides.

The reminder comes following reports of crop damage in certain situations over the past couple of summers, where growers have been using metolachlor herbicides to tackle weeds before planting.

Mark Congreve, senior consultant with Independent Consultants Australia Network (ICAN), said weed competition during the establishment phase of sorghum can result in poor establishment, uneven maturity and harvest delays.

“Weeds need to be managed well to achieve high yields. Where weeds compete with the crop for nutrients and moisture, a yield penalty often occurs,” Mr Congreve said.

“A lack of post-emergent herbicide options for grass control in sorghum means that pre-emergent control is often required and metolachlor-based herbicides, such as Dual® Gold, Clincher® Plus and Bouncer® are frequently used.

“To reduce the potential damage to seedlings that come into contact with this herbicide, a seed safener such as Concep® II is required.

“When metolachlor-based herbicides are applied at or prior to planting, it is highly likely that the germinating sorghum seedling will come into contact with some of the herbicide during germination and emergence.

“As germinating sorghum seed absorbs moisture from the soil, it will take up some metolachlor herbicide that is dissolved in the soil water.

“To successfully germinate and establish, the seedling needs to be able to metabolise this herbicide before toxic effects are expressed.

“Concep® II increases a seedling’s ability to metabolise metolachlor, therefore reducing the toxic effects. Growers should follow mixing and application guidelines to get the most out of Concep® II.”

Mr Congreve said Concep® II should be applied to the seed prior to planting – growers can order sorghum seed that is already treated or treat their sorghum seed on-farm.

Mr Congreve said a number of factors increased the chance of sorghum injury from metolachlor-based herbicides, including:

• Rainfall or irrigation between planting and emergence wetting down to the seed zone, especially where waterlogging occurs.
• Sandy/coarse/low organic matter soils are at higher risk of herbicide damage.
• The germinating seedling is under stress (e.g. waterlogging, cold shock, insect damage).
• Maximum application rates.
• Marginal soil temperature at planting.
• Defined planting furrows that, with rainfall, act to concentrate herbicide over the crop row.
• Shallow planting depth.

Mr Congreve said as well as using high quality seed treated with Concep® II seed safener, closing up of the planting slot to avoid herbicide coming into contact with the sorghum seed would also help reduce the chance of sorghum injury.

For more information, visit GRDC website