FARMERS could be forgiven for thinking they were at The Alamo at last week's regional Crop Updates meeting at Binnu.
The reason was the knowledge of a lack of bullets to fire at weed "enemies".
And Landmark/Crop Circle consultant Grant Thompson cautioned against over-use of group H "bullets" to control wild radish.
"There are concerns of using multiple group H sprays in one season," he said.
"It is very likely to hasten the onset of H-resistance so you need to find alternatives."
But what alternatives?
According to Mr Thompson, resistance to wild radish is growing because of a large selection pressure using cheap chemicals, resulting in several germinations of radish a season.
Simazine is on the way out along with Brodal and there are severe limitations to what we have left," he said.
"There are also multiple-resistant populations (sprayed with two or more different chemicals) so we have two or three herbicide groups not working.
"There are no silver bullets for radish.
Among the chemicals identified as dud "bullets" for radish are 2,4D, atrazine, chlorsulfuron (Glean), DFF (Brodal) and a sub-group of group B (Intervix).
The new "bullets" are Precept and Velocity (group H) which have been effective in controlling wild radish but are now being flogged, according to Mr Thompson.
"What we are seeing is that genes from radish can cross-pollinate and quickly accumulate resistant genes in a paddock, called stacking," he said.
A recent Australian Herbicide Resistant Initiative Wheatbelt radish survey revealed radish resistance to chlorsulfuron (84 per cent), 2,4D (76pc), Intervix (49pc) and DFF (49pc), atrazine (1pc), with nil results for pyrasulfatole with bromoxynil and glyphosate.
Most resistant paddocks were in the central and northern Wheatbelts but the worrying trend throughout the Wheatbelt is multiple-resistant plants or what Mr Thompson calls stacked resistance.
"It's a form of multiple resistance where plants in a population independently develop resistance to herbicides with different modes of action and then through co-existence, eventually interbreed to produce individual plants resistant to more than one herbicide group," Mr Thompson said.
He cited radish survivors from a brew of Jaguar (800ml/ha), MCPA LVE 950ml/ha) and Logran (10g/ha).
"The sampled radish in the wheat crop found 75pc of survivors to Jaguar and 100pc to MCPA and Logran," Mr Thompson said.
"Previously the farm had used 2,4D, Ally and Glean but a consultant recommended the new brew, chemicals which the farmer had never used before."
In three large scale GRDC-funded wheat trials held over recent years, Mr Thompson said there was a distinct yield advantage (between 400klg/ha and 500kg/ha) if an early two leaf spray was followed up with any number of the five leaf spray options.
"Yields ranged from 2.63t/ha to 3.06t/ha when only one late spray was applied," he said. "When the two spray strategy was implemented yields ranged from 3.1t/ha to 3.64t/ha.
"Including application costs, the early two leaf spray treatments cost between $19/ha and $29/ha.
"Given the consistent yield improvements of between 4-500kg/ha of wheat ($290t), that is an increase in net profit of about $90/ha to $130/ha."
The trials also demonstrated the difference in wild radish control using 50L/ha and 100L/ha water rates.
"Higher water rates (and subsequent additional coverage) alone increased control in a trial involving Velocity and Jaguar," Mr Thompson said.
"Both products used were contact-based herbicides and factors influencing efficacy included shading, water rate, droplet size, coverage and weather conditions."
According to Mr Thompson, Velocity achieved the highest level of control (100pc) at the two leaf stage but when MCPA was added achieved 100pc control at the five leaf stage.
"Jaguar at two leaf achieved 96pc control but if delayed to five leaf, the Jaguar and MCPA treatment fell away to 67pc," he said.
"Even though there is high LSD, it indicates the variability in efficacy when you spray later.
"The Velocity-based treatments were also 13 to 15pc higher-yielding than the Jaguar-based treatments."
Mr Thompson said the key messages were:
p Small weeds are easier to kill.
p Spray as early as possible before shading.
p Know your resistance status.
p Be prepared to spend some money.
p Timing of the second spray is important.
p It is profitable to spray early.
p Resistant weed can be controlled.
p There are alternatives to two hits of Velocity and Precept (group H).