It's time to get spraying

WA growers are urged to control summer weeds as soon as possible, even if it means getting out the boomspray while completing harvesting programs.

Significant rainfall in late spring and summer has triggered widespread germination of weeds and 'volunteers' from the 2011 crop.

Grains Research and Development Corporation (GRDC) western panel member and former farm consultant Ralph Burnett acknowledged that it was difficult for some growers to spray weeds while finishing weather-affected harvesting programs.

But he said research and many years of farmer experience showed early spraying provided the most benefits, and it was a false economy to delay.

"By doing it later, valuable moisture and nutrients are lost from the soil, the weeds will be larger and more expensive to kill, and you will have created a 'green bridge' allowing pests and diseases to carry over to the next crop," Mr Burnett said.

"It is better value to spray now, even if you have to follow up with one or two more applications, than applying a single spray just before seeding - by then you will have missed the boat.

"The best time to spray summer weeds is early in the morning, when they will accept the herbicide, and generally you can't harvest anyway at that time of the day."

Mr Burnett said the longer the break between killing summer weeds and seeding the 2012 crop, the better the 'fallow effect'.

"Fallow is very effective - our fathers used a plough, but now we use a boom to create a superior fallow," he said.

"It is preferable to create a break of at least three weeks during which there is no green plant matter capable of hosting insects, nematodes, foliar diseases and fungal root diseases.

"The longer the gap between spraying and sowing, the less effect the herbicides may have on the emerging crop."

Mr Burnett said uncontrolled summer weeds and crop volunteers also significantly depleted soil moisture and nutrients that would otherwise be available to following crops.

Mr Burnett said GRDC-supported research in WA and NSW found that removing weeds shortly after they began to emerge could preserve 50 to 75 millimetres of soil moisture.

"Researchers have also identified yield losses of 0.5 to one tonne per hectare in cereals where the green bridge remained uncontrolled up to seeding," he said.

"Nutrients such as nitrogen used by the green bridge are no longer available to crops at seeding, even if the green bridge is later killed by herbicide."

For information about summer weed control, growers can download a GRDC Green Bridge Fact Sheet at www.grdc.com.au . For information on rust, go to www.rustbust.com.au or www.grdc.com.au/rustlinks .