Integrate winter fleabane control
From the March 2012 edition of Agriculture Today.
Hanwen Wu inspects herbicide control efficacy on fleabane in a degraded lucerne pasture. He says winter control is most effective using a mixture of residual herbicides, with the option of strategic tilling. (Photo: Bill Littlewood)
Recent increases in fleabane infestations have spurred the need for better understanding and improved management.
Eight fleabane populations are confirmed resistant to glyphosate in northern NSW and southern Queensland and the weed is now severely infesting cropping lands, roadsides and other non-agricultural areas.
Focusing control efforts on the major emergence flushes in winter and spring using mixtures of knockdown and residual herbicides, with the option of strategic tilling in fallows, will be most effective.
“Integrated management, incorporating chemical and non-chemical control options should be adopted to manage fleabane and prevent the rapid development of herbicide resistance,” said Wagga Wagga senior research scientist Hanwen Wu.
“A landscape approach, targeting crops, pastures, fallows, fence lines and roadsides is necessary, otherwise re-infestation and new infestation in untreated areas will occur.
“Flaxleaf fleabane produces massive amounts of seeds that spread rapidly on the wind and a small percentage of survivors is enough to maintain high seedbank levels in following years.
“Stopping seedset is of paramount importance, but unfortunately, many mature plants are left unchecked in summer and continue to produce seed.”
The unique protective leaf structure of mature fleabane (Conyza bonariensis) restricts foliar herbicide uptake, so use of residual herbicides is an important strategy.
Residual herbicides often control multiple flushes of fleabane in winter cereals, pastures and fallows but care should be taken when using them as they may restrict the choice of rotational crops.
Herbicide mixtures are generally more effective than single herbicides such as glyphosate or paraquat.
Adding a suitable phenoxy herbicide to glyphosate greatly improves control in fallows.
Two Wagga workshops
Leading national scientists and agronomists will present research updates on key issues associated with fleabane management. Growers and advisors are welcome to attend, at the CSU Convention Centre, Wagga Wagga, March, 21-22.
- Register at www.grahamcentre.net
A timely follow up application of paraquat will help achieve consistent results.
Applications of tank mixtures of paraquat and triazine herbicides (for example, atrazine or simazine) in early July provide excellent control of seedlings in established lucerne-based pastures, but will damage undersown subclover and chicory.
Dr Wu said fleabane was a poor competitor.
“Growing competitive crops and avoiding wide row spacing can help reduce fleabane populations,” he said.
“Another potential control tactic is strategic tillage in fallows.
“Fleabane seed is very sensitive to burial and seedlings will only emerge from seed on or near the soil surface.”
Aggressive re-growth of mature plants after slashing or grazing and the prolonged emergence during winter and spring requires multiple control actions.
Seedlings are easier to control, so it is best to apply herbicides when the plants are small and actively growing.
Fleabane prefers cool and moist conditions and temperatures between 20-25°C for optimum germination.
It cannot germinate below five degrees or above 35°.
This is why fleabane emerges mainly in winter and early spring, with limited emergence in summer and the dry autumn period in southern NSW.
Contact Hanwen Wu, Wagga Wagga, (02) 6938 1602, firstname.lastname@example.org