Control summer weeds early

Author: Rachel Bowman | Date: 20 Dec 2012

Over head nozzle spraying water

Northern region grain growers are being urged to get on top of summer weeds early in fallow paddocks in order to minimise nutrient and moisture loss and increase the yield potential of next season’s winter crops.

Key to maximising the effectiveness of summer herbicide regimes is good planning and the correct set-up of spray equipment, including nozzle height and droplet size.

New research has shown that coarser droplet size can be more effective in controlling weeds in summer fallow situations, and can reduce the risk of spray drift.

“If spraying to conserve soil moisture and retain nutrients over summer, early weed fallow control can increase the yield potential of future crops,” GRDC Northern Panel Chair James Clark said.

“Waiting for later germinations of summer weeds may not provide the same return on the dollars invested in control measures as a spray program that starts early.

“And with many northern region farmers also growing summer crops, it is doubly important that farmers manage both weed populations and minimise the risks of spray drift.”

To assist northern grain growers, the Grains Research and Development Corporation (GRDC) has recently released a Summer Fallow Spraying Fact Sheet, compiled by well-known spray application specialist, Bill Gordon.

Mr Gordon said that as part of the planning process, farmers should ensure that the sprayer is ready to go as soon as it is needed.

“This means that the sprayer and the mixing equipment are clean and decontaminated, the correct nozzles are available and calibrated, and the machine is functioning correctly,” he said.

“Farmers must also select an application volume to match the target weeds, stubble situation and the herbicides’ mode of action.

“The majority of fully translocated herbicides require the use of a coarse spray quality, particularly Group M, Group I and Group B herbicides.”

Summer fallow trials over the last six years have shown that equivalent efficacy can be obtained for Group I and Group M products with extremely coarse droplets, provided that nozzles are operated appropriately (for example, sufficient pressure with the air induction types).

For summer spraying, coarse spray qualities and larger generally perform as well as, or often better than, medium spray qualities.

“Extremely coarse spray qualities also reduce drift potential by reducing the amount of airborne droplets by up to 80% of those produced by a standard coarse spray quality,” Mr Gordon said.

“This is important to remember in situations where sensitive summer crops are grown nearby, in order to minimise the risk of off-target movement of product.

“Larger droplets also increase the time that the chemical stays in solution before the water fully evaporates, so they are useful in harsher spraying conditions.”

Other factors to consider for summer spraying include: correct mixing order and suitable spray water quality; avoiding surface temperature inversion conditions; and recording the application details and the results of the spray job.

“Often the most important factor is getting the timing right in relation to weed susceptibility and using a robust rate of product,” Mr Gordon said.

“It is worth remembering that delayed control, which will result in reduced moisture and nitrogen in the soil, is better than no control at all.”

The GRDC Summer Fallow Spraying Fact Sheet is available at


    PHOTO CAPTION: Northern region grain growers are urged to get on top of summer weeds early in fallow  paddocks

    For interviews:

    James Clark, GRDC Northern Panel Chair
    0427 545 212

    Bill Gordon, Bill Gordon Consulting
    0429 976 565

    Rachel Bowman, Cox Inall Communications
    07 3846 4380 / 0412 290 673

    GRDC Project Code BGC0002

    Region National, North