Australia
August 3, 2015

Zero till farming and wind-blown seed dispersal, coupled with glyphosate resistance has seen fleabane develop as one of the major broadleaf weeds of northern cropping systems. Effective management of fleabane will require a combination of good agronomy; non-herbicide tactics (e.g. crop competition) and strategic use of herbicides.

Understanding the ecology of fleabane is the first step in designing an integrated management program. Research undertaken by Queensland Department of Agriculture and Fisheries (DAF) shows that:

• To germinate, seed is required to be on the soil surface. Fleabane will not germinate when buried more than 1cm deep. Germinations are significantly reduced when confronted with crop or pasture competition.
• Major flushes occur after a significant rainfall event when temperatures are in the 10 to 30oC range (20 to 25oC is preferred), which typically means spring and autumn germinations in the northern region.
• Seed persistence is short. Seed viability is typically less than 2 years when left on the soil surface.

A concerted program to prevent seedbank replenishment for two years can significantly deplete the seedbank in a zero tilled system, leaving growers to predominantly deal with emergence from new seeds being blown into the paddock from adjacent areas.  

Integration of herbicides into the management program is likely to be critical to prevent seedbank replenishment. More than 10 years of paddock research and extensive registration activity has led to the point where there is now a range of effective integrated solutions available to control fleabane in many of the situations faced by northern advisers. Key strategies proven to be effective include:

Control in the winter cereal crop

Controlling fleabane in winter crops is a critical management tactic. If fleabane establishes in the winter cereal crop, the tap root will continue to grow over winter and the plant will be very difficult to control after harvest in early summer.

There are a number of registered herbicides available to provide knockdown and/or residual control in winter cereals. These include:

• Amicide® Advance 700 - Knockdown in wheat, barley, rye, triticale. Up to 6 leaf weed size.
• FallowBoss® Tordon® - Knockdown in winter cereals. Up to 8 leaf weed size.
• Lontrel® Advanced - Knockdown and residual control in wheat, barley, oats, triticale. Up to 5cm rosettes.

Herbicide options with residual activity

Using residual herbicides in the fallow or within the cropping system is often the most effective strategy to run down the fleabane seedbank. Residual herbicides should be in place to control the expected autumn and spring germinations.

Herbicide options include:

• Balance® - Residual control in fallow.
• Diuron (various products) - Pre-emergent and layby use to control annual broadleaf weeds in irrigated cotton.
• FallowBoss® Tordon® - Residual control in fallow prior to winter cereals or sorghum (see label for mixing partners).
• Lontrel® Advanced - Knockdown and residual control in winter cereals, fence lines and roadsides. Up to 5cm rosettes.
• Terbyne® Xtreme - Residual control in fallow prior to mungbeans, soybean, wheat, barley, oats (NSW & Qld only).
• Various products containing 2,4-D + picloram - Knockdown and residual control in fallow prior to planting winter cereals in mixtures with glyphosate (NSW & Qld only).

Knockdown in fallow

A range of herbicides are registered for knockdown control of fleabane in fallow. All of these registrations are limited to application targeting weeds in the rosette stage.

Herbicide options include:

• Alliance® - Knockdown in fallow. Maximum 6 leaf weed size.
• Amicide® Advance 700 - Knockdown in fallow when used in mixtures with Weedmaster® DST. Up to 12 leaf weed size and prior to stem elongation.
• Basta® - Knockdown in fallow. 2 to 6 leaf weed size.
• FallowBoss® Tordon® plus glyphosate - Knockdown and residual in fallow prior to winter cereals or sorghum. Up to 10cm rosette.
• Sharpen® - Knockdown control in fallow and non-crop areas. 1 to 6 leaf weed size (suppression of 6 to 30 leaf weed size).
• Various products containing 2,4-D + picloram when mixed with glyphosate - Knockdown and residual control in fallow prior to planting winter cereals (NSW & Qld only).

Advanced fleabane will require a double knock application to provide satisfactory control and stop seed set. Amicide® Advance 700 and FallowBoss® Tordon® contain additional label registrations for double knock application when followed by paraquat and Spray.Seed® respectively.

Use of optical spot spray technology in fallow

Where scattered plants are present in fallow, the use of optical spot sprayers (e.g. WeedSeeker®, Weedit®) can be an effective management tool.

Herbicide options registered to control fleabane (weed cover up to 30% of the paddock) include:

• Alliance® - Rosette to flowering plants.
• Amicide® Advance 700 - Rosette to flowering plants.
• Nuquat® - Rosette to flowering plants
• Trooper® 75-D - Rosette to flowering plants.

Note: Avoid applying a tank mix of 2,4-D and paraquat at high application rates registered for optical spot spraying, as antagonism has been observed.

As all farming systems and crop rotations will be different, it is important for advisers to develop customised strategies for their growers. An example of an effective strategy to deplete the seedbank in the soil may look something like the following:

• Late summer / early autumn – apply FallowBoss® Tordon plus glyphosate in the fallow (a double knock will be required for complete control)
• Late autumn – sow a winter cereal. Aim for narrow rows and even plant stand to maximise crop competition. Barley will provide increased early season competition, compared to wheat.
• Winter – monitor the crop during tillering for any fleabane germinations. Control with a registered in-crop option where required.
• Harvest – monitor the crop for existing plants. If present, control with a double knock application immediately after harvest, adding a registered fallow residual option to the second knock. If there are no existing plants then only apply the residual herbicide.
• Monitor the fallow over summer for any escapes to prevent these going to seed and replenishing the seedbank. Access to an optical spot sprayer will allow for cost effective control of low weed densities.
• Avoid broadleaf crops as the following rotation, due to the lack of in-crop selective herbicides available to control any escapes. Ideally follow the winter cereal with sorghum or maize or another winter cereal, using an effective pre-emergent herbicide. If required, also apply an in-crop knockdown.  
• By the second summer the seedbank should be significantly depleted. Continue the use of optical sprayers in the fallow to control any survivors or new wind-blown introductions.

Selected herbicide options registered for the control of fleabane, their mode of action group and active ingredient(s). Refer to product labels for application rates and detailed instruction for use.

Note: Where brand names have been indicated, this is indicative that only this brand contains a label claim for control of fleabane via a specific use pattern.

Further information:
Mark Congreve ICAN 0427 209 234 mark@icanrural.com.au
Michael Widderick Principal Research Scientist (Weeds) Qld DAF 07 4639 8856 / 13 25 23 michael.widderick@daf.qld.gov.au
GRDC Project code: ICN00016 and UQ00062

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Region North

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Published: August 3, 2015