Summer weed control in a high input cost year

WEEDSMART is still encouraging farmers to spray their summer weeds despite the high cost of glyphosate.

Western extension agronomist Peter Newman said spraying summer weeds is one of the greatest returns on investment in modern agriculture — preserving soil nitrogen and moisture reserves for the following crop.

“As Dr James Hunt’s research at La Trobe University, Victoria showed, the top foot of soil will dry out over summer, regardless of how much stubble is on the soil surface, but transpiration by summer weeds is the only mechanism that can remove water from below 30 centimetres,” Mr Newman said.

“I believe it will still be worthwhile because summer spraying preserves soil nitrogen, which is also very expensive, and the outlook for high grain prices is strong.

“In 2010 to 2012, Colin McMaster from NSW DPI did some great research which showed the measurable benefit of summer weed control was $7.20 per dollar invested, at a time when both herbicide costs and grain prices were lower than they are today.

“If we double the 2010-12 cost of a summer herbicide spray program and use the 2010-12 grain prices of $240/t wheat and $500/t canola, the return on investment drops from $7.20 per dollar spent on spraying, to about $3.50.

“If we then increase the wheat price to $360/t and canola to $750/t, and keep the chemical costs high, the benefit cost increases to about $5.50 per dollar spent — still a worthwhile return on investment when considering just the benefit of the conserved soil moisture.”

The second big benefit to flow from summer weed control is increased soil nitrogen, Mr Newman said.

“The WeedSmart Big 6 promotes tactics to keep weed numbers low because that is the best way to tackle herbicide resistance and grow more crop,” he said.

“The double-knock tactic is a highly effective tool that is worth considering, even at higher chemical costs currently affecting growers.”

For more information about summer weed management, visit www.weedsmart.org.au.