Australia
July 3, 2014
By GRDC Manager Regional Grower Services – North, Sharon O’Keeffe
Weed control practices have been foremost in growers’ minds following a warmer-than-usual start to the winter season.
While winter conditions have now arrived in the north, an unusually warm June prompted a rapid growth response in wheat crops and weeds, forcing growers to implement weed control strategies early and effectively to avoid problems as the season progresses.
With the recent cold change causing frost events, growers should contact their agronomist to discuss the consequences of herbicide applications.
Frosts within a few days prior to and post spraying can have severe impacts on herbicide efficacy and crop safety.
Grains Research and Development Corporation (GRDC) trial work has proven that weeds have a significant impact on crop productivity, increasing plant competition for moisture and nutrients and reducing yield.
Planning a coordinated and effective in-crop strategy to control weeds, particularly problem grassy weeds like wild oats, will help growers maximise crop yields while reducing the likelihood of developing a herbicide resistance problem on-farm.
Growers are urged to be mindful of their Group A herbicide use as there are already resistance issues with some of the commonly-used Group A chemicals.
Rotating modes of action wherever possible is a critical part of any weed management program as is checking the efficacy of any spray application for survivor plants and eradicating those plants immediately using an alternative and preferably non-herbicide tactic.
In cases where resistance status of weed outbreaks is known or there have been problems in the past with the efficacy of Group A chemicals, growers should consider rotating to a ‘den’ Group B herbicide or a combination of Groups A and B herbicides, with the aim of using only one Group B chemical within three years.
The efficacy of herbicide applications will also be significantly affected by mixing and spray practices.
Growers need to spray weeds early, use robust rates and ensure they adhere to best management spray application recommendations on water rate, environmental conditions, droplet size and boom height.
The use of best practice similarly applies to tank mixes – water quality should be optimum in terms of pH, total hardness, bicarbonate levels and either total dissolved salts or salinity; and adjuvants should be selected according to compatibility with the target weed and herbicide, including adjuvants in other products within tank mixes.
A weed control strategy that incorporates industry recommended best practices, considers the impact of chemical applications on the whole farming system and uses an integrated program of herbicide and non-herbicide tactics is growers’ best defence against the development of herbicide resistance.
Information on herbicide resistance and integrated weed management strategies is available from www.weedsmart.org.au.
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