2-4 D resistant wild radish
Herbicide resistance development in problem weed species is an ongoing problem facing growers, advisors and the grains industry as a whole.
Every year the annual cost of weed control for Australian growers about $3.3 Billion1 and one of the prime suspect weeds contributing to this in Western Australia is wild radish (Raphanus raphanistrum).
Wild radish is one of the most widespread, highly adaptive and competitive weed species in Australian cropping regions with each mature plant able to produce up to 50,000 seeds.
70 per cent of these seeds will also remain dormant in the soil in the season immediately following the seedset year. Its high seedset ability coupled with its genetic diversity and ability to out-cross readily, means it had been able to build up herbicide resistance and at times quite quickly.
Common broadleaf herbicides such as 2-4,D Ester and other Group I phenoxy herbicides were long used as the main method of chemical control for wild radish and other broadleaf weeds in cereal paddocks. Due to continual use of the same mode of action (MoA) herbicide, in paddock radish populations have eventually had susceptible plants selected out leaving those that have developed resistance becoming the majority.
In wild radish part of this resistance appears to be caused by resistant plants developing the ability to prevent movement of the herbicide within the plant from the treated area (eg. the leaf hit by the chemical). 2,4-D must move to the growing point of the plant to kill it. A resistant radish plant essentially “cuts-off” the treated part of the plant, holding the chemical there and continues growing as normal.
So, what can growers do to combat this? Management strategies include (but aren’t limited to):
- Know your Enemy! If you suspect herbicide resistance; take a plant or seed sample and get it herbicide resistance tested. There are multiple laboratories in Australia providing this service.
- Rotate herbicides and use multiple MoA herbicide mixes
o Most common Post-Emergent Herbicide strategies now include Group C,F,I herbicides and rotate in Group H and G as well.
- Rotate crop types to allow for alternative chemical options and/or improved crop competition
- Apply Post-Emergent Herbicides at label rates as early as possible/recommended to small weeds
o Even weeds developing resistance are much easier to control early.
- Harvest Weed Seed Control (HWSC) – Use options such as seed destructors to reduce seed set. Chaff carts and windrowing residue to bail or burn are also other options
- Tillage – Where appropriate, tillage is still an option for controlling weeds such as Wild Radish.
o Moulboard Plowing is very effective at burying radish deep below a viable depth for the seed to germinate from
- Practice good farm hygiene – always plant clean seed to prevent further introduction of weed species to the paddock. Prevent transfer of soil residue.
If you suspect herbicide resistance in radish or other weeds, contact your local Elders Agronomist who can organise herbicide resistance testing as well as assist you in a management strategy to combat resistant weeds.
Elders offers a range of crop protection products.
Article written by Elders Wongan Hills senior agronomist Cameron Smith.