Excellent establishment of all crops and the strategic use of highly competitive cultivars are powerful management practices that can limit the opportunities for herbicide resistant weeds to take hold.
Lead scientist and director of the Graham Centre for Agricultural Innovation at Charles Sturt University, Professor Deirdre Lemerle said the genetic control for competitiveness involves multiple genes and is too complex to easily select for in most crops.
“Breeding for competitive advantage has not generally been considered a key aspect of plant breeding programs in the past,” she said. “We now know that it is an important agronomic trait and it is being considered in more breeding programs.”
“When it comes to crop establishment, our studies have shown there is no yield penalty for planting at higher sowing rates, even in low rainfall environments.”
The allelopathic effect of crops such as canola on weeds is a new area of research at the Graham Centre.
“The most competitive crops are still unlikely to prevent the spread of herbicide resistant weeds,” said Professor Lemerle. “Well established, competitive crops are known to restrict weed growth and so these strategies are included in the WeedSmart 10 Point Plan.”
“If the crop is competitive, the herbicide applied to the crop is likely to be more reliable—managing to minimise herbicide resistance must be seen as a package because none of the weed control options are effective on their own.”
What are the most competitive crops?
Short answer: Triticale, barley and rye.
Longer answer: The competitive capacity of crops can be measured. Triticale, barley and rye are more competitive than wheat and some wheats are more competitive than others. Pulses are less competitive than cereals and the competitiveness of brassicas is very dependent on sowing time. Choose varieties that have rapid early growth and early canopy closure.
What is the best way to improve crop establishment?
Short answer: Aim for optimal crop density.
Longer answer: If weed pressure is a concern, choose a seeding rate at the higher end of the recommended range for your crop. Calibrate your equipment and use only clean, fresh, viable seed. In wheat, higher density planting causes fewer tillers per plant but larger grain, giving no yield penalty. Even though wider row spacing may be beneficial in conservation cropping systems for ease of planting and where stubble can reduce weed emergence, crops at wider rows are less competitive.
How can allelopathy help?
Short answer: It can inhibit the emergence and growth of some weeds.
Longer answer: Current research is investigating the potential for crops like canola to inhibit the growth of annual ryegrass. There is a large difference in the allelopathic effect of different canola cultivars. A cultivar may be chosen specifically to inhibit the growth of a target weed as part of a three to five year weed management strategy.
How to ask a WeedSmart question
Ask your questions about the spread of herbicide resistance, or any herbicide resistance management strategy, using this blog or using Twitter @WeedSmartAU.