By Lisa Castleman, District Agronomist, NSW DPI (Lockhart) Ph: 0427 201 963
This weed is fairly appropriately named, as pesky as a flea and the bane of last summer and more to come.
What do we know about it?
It is a hairy and dull green plant known to be a prolific seeder as one plant can produce as much as a 110,000 seeds. It often reaches a height of 1 metre, while other species such as Canadian Fleabane will grow to a height of 1.5m and Tall Fleabane can reach 2 metres high.
About 80% of those seeds are very likely to come up. Those seeds sitting on the surface or buried less than 2cm deep are more likely to germinate. Fleabane can germinate in a range of conditions which include good soil moisture and temperatures less than 35 degrees Celcius. This puts the odds in its favour because it can germinate in any of our four seasons. Peak emergence is in late winter and throughout spring. It has certainly shown itself capable of growing through 2010 and 2011 with a wet summer in between.
The plant itself has a number of buds or growing points at its base. This is why you can spray, slash or graze it off once, and it will recover. While it might lose green leaf, such as when dessicated by a herbicide, the next bud will contain enough energy reserves, to shoot up and grow new leaves.
The weed has been problematic in Northern NSW over the last few seasons. Fleabane utilises valuable moisture and soil nutrients in any season. The need to find the best method of control has prompted interest from farmers, agronomists and researchers alike.
In our own backyard we have Dr Hanwen Wu based at Wagga Wagga (WWAI), who was previously working on the biology and management of Fleabane in Northern NSW and Queensland. He spoke recently at the NVT Field Day this Spring at Lockhart on the weed to a very interested audience of growers. He said there has been an ‘increased incidence of the weed with minimum and zero-till farming systems’.
Fleabane flourishes in bare fallow, on firebreaks or in poorly competitive crops.
Dr Hanwen Wu said “it is very important to spray Fleabane at the seedling stage”.
Some tips for control of Fleabane:
Don’t ignore it as a serious and problematic weed.
Don’t rely on one herbicide application of any herbicide achieving a 100% kill.
Spraying when the plant is more mature than a seedling or past the rosette stage is not ideal, however, it can’t be ignored.
Achieving even 90-97% control from one herbicide application is not regarded as a success due to surviving plants being able to reshoot and continue growing.
Barry Haskins, the District Agronomist at Hillston with NSW DPI has just put out a new You Tube video on Fleabane in Fallows on the NSW DPI website on the 5 December.
One of Barry’s take-home messages from a number of trials is their increased success from adding an oil instead of LI700 to the tank mix (which includes Glyphosate) for control. With Fleabane being a hairy plant it’s probably not surprising. Some previous trial work in Queensland hinted that more work needed to be done on finding the right surfactant or oil to be added for control of this plant. His caution is to be aware that an oil in the tank-mix may reduce or affect the efficacy of Glyphosate on some grass weeds in fallow.
Barry’s observations from his trials in the Hillston District were that you can’t rely solely on a single knockdown herbicide such as Glyphosate in the first herbicide application to achieve a satisfactory result.
In research trials across Northern and Southern NSW Dr Hanwen Wu concluded that Glyphosate alone was not very effective unless the seedlings were very small and less than 2cm in diameter, regardless of the rate, spray volume or adjuvant.
In a fallow situation post harvest there are often a number of weeds present. Growers will look to a tank-mix to control a number of weeds that are present and all using precious moisture and nutrients. It has been observed that adding a herbicide registered for other fallow weeds such as melons can increase the control of the Fleabane. For example, Surpass® or Amicide® containing 2,4-D amine may be important additions and required for the control of melons over summer. Likewise the tank-mix could include a herbicide such as Ally® where it is required for the control of sowthistle or wireweed in the same paddock as the Fleabane.
Alliance® is a registered option for Fleabane Control at Fallow commencement and/or maintenance, as per Table 5 on page 32 in the 2011 Weed Control in Winter Crops. Alliance is a combination of Amitrole at 250g/L and Paraquat at 125g/L. Alliance was included in Barry Haskin’s trials and its performance on fleabane was mentioned in the You Tube video.
The most important Take-Home message when planning Fleabane control is to use a ‘Double-knock strategy’.
Barry Haskins also reinforces the importance of using water rates greater than 80 litres/hectare for your double-knock strategy. Again, previous work by DPI & Fisheries in Queensland reinforces this finding.
The second or follow-up application should be not closer than seven days apart. Ideally it will be about 10 days after the first but could be between 7-21 days after the first application. If conditions at spraying were dusty or plants were moisture stressed and slow to take up the herbicide then there may be cause to wait longer between the two sprays.
Other non-herbicide methods such as grazing, slashing or cultivation will help run the plant’s energy reserves down but are unlikely to achieve control on their own and will mean many more paddock passes.
The earlier you begin control the more likely you are to stop the plant seeding and start running the seed-bank down.
The You Tube Video can be viewed at
http://www.youtube.com/user/NSWAgriculture?feature=mhee#p/u/0/YYgZKzNeOIc
Even if you are not that computer savvy I think you will enjoy it. It is nearly as good as going to a live field Day and seeing the results for yourself. The video takes just 5 minutes to watch. There are lots of results discussed so have a pen and paper handy.
Acknowledgements:
Dr Hanwen Wu, NSW DPI, Wagga Wagga
Barry Haskins, NSW DPI, Hillston.
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