GOOD spring rains and follow-up falls since have allowed weeds to establish earlier and grow larger during summer, increasing the burden for SA farmers.
Mallee agronomist Michael Moodie said some croppers were forced to start spraying during harvest to get on top of weeds.
“Normally it’s rain after harvest that gets weeds established,” he said. “But this year it was rains before harvest that has got weeds going.
“Some weeds will be larger due to the longer growing period so it’s important growers adjust rates and make sure they are spraying in optimal conditions.”
Mr Moodie cautioned croppers using higher chemical rates.
“Be mindful of residual issues and the crop you plan to sow next season,” he said.
Mr Moodie said research showed benefits from killing weeds outweighed the costs.
The GRDC Water Use Efficiency Initiative found that controlling summer weeds delivered an average increase in seasonal water use efficiency of 60 per cent, delivering an average return of $5.60 for every dollar spent on summer weed control.
“Research also shows it is not just moisture that the weeds rob from the plants, but also the availability of nutrients, such as nitrogen,” Mr Moodie said.
“Maintaining those nutrients in the soil for the next crop is as important as water.”
Summer weed and crop volunteer management was also important in reducing pests and diseases surviving on the “green bridge” between crops.
Rusts and aphids are of particular concern, which has prompted some experts to encourage croppers to go “Free for February”.
SARDI pathologist Hugh Wallwork said a month of no green growth was required to prevent disease and pest survival. But neighbour collaboration would be needed.
“Diseases do not respect farm boundaries, so if a grower’s neighbour has volunteers infected with leaf rust, there has effectively been no break,” he said.
“The month is also key because some regions are still harvesting in January, and some growers want to sow early March, so February is the only chance for a full pest and disease break.”
Lameroo cropper Peter Maynard started spraying weeds from the new year.
“We’re about two-thirds of the way through the program,” he said.
“But some paddocks we have had to spray up to three times, mainly the hay paddocks, because of spring and summer rains.”