Flaxleaf fleabane is a major weed of summer fallows and pastures across Australia; it is a native of South America and is thought to have been introduced in the 1840’s. Fleabane has only become a weed of significance since the advent of minimum tillage practices, with its population range in cropping areas increasing year on year (often originating from roadside populations).
Minimum till provides optimal conditions for fleabane as the seeds are only capable of germinating in the top 1cm of soil, with the removal of tillage allowing the majority of seeds to remain on the surface. Fleabane generally prefers 20-25 oC temperatures and requires light exposure for germination, predisposing it to spring/summer germination events.
Fleabane plants possess a strong taproot system, enabling it to chase deep stored moisture, rendering its presence in summer fallows particularly detrimental to following crops. A combination of this strong taproot system, ability to accumulate starches, hairy leaf surface, thick cuticle, low stomatal density and woody characteristics make established fleabane plants exceptionally difficult to control with single pass herbicide strategies (Wu et al. 2007; Fleet et al. 2015; DAF 2012).
In 2014, Imtrade Australia undertook a replicated field trial to investigate some potential herbicide options for controlling Fleabane in a single pass. The trial was conducted post harvest of a wheat crop where Fleabane has germinated under the crop canopy.
Table 1: Comparison of treatment means. Mean percentage brownout of flaxleaf fleabane
Table 2: Comparison of treatment means. Mean fleabane plants per m2.
All treatments except for IMTRADE AMITROLE + IMTRADE BROMOX 200 provided varying levels of control when compared to the untreated control.
IMTRADE ERADICATOR 450 + IMTRADE LV ESTER and IMTRADE ERADICATOR 450 + IMTRADE RALLY + STARANE ADVANCED treatments exhibited statistically equivalent control of flaxleaf fleabane across all timings. While these treatments were statistically equivalent to IMTRADE PARA-TROOPER applied at 2.4 L/ha; PARA-TROOPER was the only treatment which provided 100% control of flaxleaf fleabane.
IMTRADE RALLY clearly aids in the brownout of flaxleaf fleabane when combined with IMTRADE ERADICATOR 450, exhibiting a significant increase in efficacy at 77 DAT when compared to IMTRADE ERADICATOR 450 alone at equivalent rates.
When IMTRADE LV ESTER was added to IMTRADE ERADICATOR 450, a statistically significant increase in efficacy at 42 and 77 DAT timings was noted when compared to IMTRADE ERADICATOR 450 alone. It also provided a statistically significant increase in efficacy over the IMTRADE RALLY + IMTRADE ERADICATOR 450 mix at 77 DAT. This indicates that a 2, 4-D component provides superior control of flaxleaf fleabane compared to a clopyralid component at registered rates in combination with glyphosate.
Combining IMTRADE RALLY and Picloram generally provided poor control of flaxleaf fleabane, with the addition of IMTRADE ERADICATOR 450 required to provide equivalent control to 2, 4-D mixes.
The addition of STARANE ADVANCED (fluroxypyr) significantly improved the efficacy of any mix partner in a treatment.
The results indicate there are single pass herbicide options available to growers to control fleabane in summer fallows. The ability to obtain control from a single pass option removes the requirement for double knocking. This reduces the man-hours and cost associated with the second pass often required to obtain commercially acceptable control of fleabane with current herbicide options.
The excellent kill obtained by IMTRADE PARATROOPER has led to further work on this product targeting fleabane across Australia, with preliminary results supporting the findings in this initial trial. While the use of PARA-TROOPER for targeting fleabane is loosely covered by the current label, Imtrade Australia has chosen to invest in a label extension to explicitly list a use rate specifically targeting fleabane. This label extension is anticipated to be approved by the summer of 2016/17.
Wu H et al. (2007) Germination, persistence, and emergence of flaxleaf fleabane (Conyza bonariensis [L.] Cronquist). Weed Biology and Management 7:3 pp 192-199
Fleet B, Preston C & Gill G (2015). Flaxleaf fleabane management in cropping systems of southern Australia. Proceedings of the 17th ASA Conference, Hobart Australia.
DAF (2012) Flaxleaf fleabane – a weed best management guide. Sourced: Click here.