Residual risk

By Country News

Grain growers in NSW are being encouraged to consider the potential impact of residual herbicides as they weigh up their summer crop planting options.

Experts warn predominantly dry conditions across much of eastern Australia’s grain belt through winter may have prolonged the efficacy of residual herbicides applied in paddocks earlier in the season.

Grains Research and Development Corporation northern crop protection officer Vicki Green said the simple fact was herbicides generally needed moisture to break down.

‘‘The dry conditions during winter may mean herbicides are present in the soil in greater concentrations than growers would usually expect going into summer planting,’’ she said.

‘‘This is not a dire situation, rather it just means growers and their advisers may have to look more closely at crop choice and variety selection ahead of planting.

‘‘Most growers will be aware of the potential risks of residual herbicides in a season like this, but GRDC does have up-to-date information available if people want guidelines to soil behaviour with regard to pre-emergent herbicides.’’

Mrs Green said when it did rain growers could also use the emergence of specific weeds as an indicator of what herbicides were still active in the soil.

‘‘Unfortunately, when it rains weeds are usually the first things to respond,’’ she said.

‘‘The upside is growers can use what weed types emerge as an indication of what residual herbicides are still in the soil.’’

■The GRDC’s Soil behaviour of pre-emergent herbicides in Australian farming systems: a reference manual for agronomic advisers is available at: or preemergentherbicides