Don't forget fenceline weed control
Date: 26 May 2015
By GRDC western regional panel chairman Peter Roberts
Growers are reminded of the benefits of controlling weeds on fencelines and other non-cropping areas while these weeds are smaller and easier to control.
Traditionally, many growers have sprayed fencelines in August or September well after their sowing and post-emergent spraying operations are over.
But Western Australian research supported by the Grains Research and Development Corporation (GRDC) has shown that delaying spraying can reduce weed control substantially and these weeds can go on to set seed.
Department of Agriculture and Food (DAFWA) researcher Sally Peltzer says that while the focus of most growers is currently on seeding operations, they should not to forget about fenceline weed control.
She says fencelines can be a ‘breeding’ ground for the evolution of glyphosate resistance.
This is due to the lack of crops to compete against weeds and glyphosate’s often repeated and late usage in these areas.
Dr Peltzer encourages growers to prevent weeds from setting seed in crop margins as uncontrolled herbicide resistant weed populations which develop in these areas are likely to become even more resistant and spread into paddocks.
As part of a GRDC funded project coordinated by the University of Adelaide, Dr Peltzer coordinated WA trials in recent seasons investigating herbicide treatment alternatives to glyphosate for weed control in crop margin areas along fencelines, firebreaks and boundaries.
Results from 11 trials over three years showed that a single application of bromacil plus paraquat in May or June provided complete control of all weeds at all sites.
While bromacil is relatively expensive, only one application was needed to control all weeds, including summer weeds, for at least one year.
But this highly residual herbicide needs to be used carefully and only where there are no trees or risk of wind erosion.
Where the use of bromacil is inappropriate, two control times are often needed – once early in the year, followed by another later in the year.
Tank mixes of residual herbicides plus a knockdown give the best control for the first application.
In trials in 2014, an application in May of either simazine plus Alliance® (paraquat plus amitrole) or simazine, 2,4-D and paraquat, followed by a second application of atrazine and paraquat in August, gave very good control.
The addition of Alliance® improved control, especially where there were broadleaf weeds.
Other research outcomes included:
- Slashing followed by a spray later in the season provided good control in situations where weeds were actively growing and there was good spray coverage
- Glyphosate can still be used but intensive monitoring and complete seed set control is required to prevent resistance from developing
- The use of cultivation as a control option generally did not work well in this series of trials but has potential in the right situation
Dr Peltzer says growers should adhere to herbicide labels and use full label rates when spraying weeds.
Sally Peltzer, DAFWA
08 9892 8504
Peter Roberts, GRDC western panel
0428 389 060
Natalie Lee, Senior Consultant, Cox Inall Communications
08 9864 2034, 0427 189 827
GRDC Project Code UA00124