Herbicide Resistance
It has been seven years since the BCG held their first Herbicide Resistance Field Day, and the thought of "it won't happen to me" has turned into the reality of it happening to virtually everyone.
It has been very noticeable last year and this year, that there have been many failure with Group A herbicides such as Hoegrass and Achieve. Bayer has brought out a new product called Hussar (a Group B herbicide) which has excellent activity on ryegrass and in many cases where Hoesgrass and Achieve failed, the crop was salvaged with Hussar. How long will this product last? Is it only a matter of time before ryegrass will be as resistant to Hussar as it is to Hoegrass and Achieve? Then what?
We must use non-selective herbicides and cultural control practices to manage ryegrass. If we do not do this, then in the next ten years, more and more ryegrass populations will be resistant to many of the herbicides we use today. This will make cropping much more difficult and in some cases impossible.
2005 BCG Herbicide Resistance Field Day |
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Please provide us with some feedback on this field day and others! | |
At the BCG Herbicide Resistance Field Day on 15 September 2005, we discussed alternative practices and demonstrated some chemical options using selective and non-selective herbicides as well as more mechanical means for controlling ryegrass.
Mark Phelan, BCG Senior Technical Officer talks about Weed-Fix, a finger harrow type weeding system.
Roy and Joan Postlethwaite host the BCG Herbicide Resistance site, 24km north of St Arnaud. Their property is 100 percent cropped with a history going back over 25 years. Their soils are mostly red loams, with some Wimmera self-mulching soils. Cereals are grown on 55 percent of the property, canola on 20 percent, and legumes on 25 percent (which includes vetch hay that the Postlethwaites class as a crop). Rainfall in the area averages 403mm long-term, with 280mm falling in the growing season.
Ryegrass was first suspected to be resistant to group A herbicides on Roy's farm in the early 1990s. Up to this time fop herbicides such as Hoegrass, Verdict and Targa had been the main control method for the weed. Following the rapid spread of resistant ryegrass across many paddocks in the mid-1990s, a new rotation was started which focused on reducing ryegrass numbers.
Roy Postlethwaite, host of the BCG Herbicide Resistance site, and Fiona Best, BCG Extension Coordinator.
Roy says that herbicide resistance can't be avoided, but it can be managed. He has had the most success with growing vetch, which is permanently in the rotation now as the main tool for ryegrass resistance management. It is grown every four or five years. Roy cuts the vetch for hay rather than green manuring it, purely to get a return, and no grass herbicides are used on it. Once the vetch is cut, the paddock is sprayed out before the ryegrass has had a chance to seed, then it is stocked fairly heavily with sheep (on agistment) to stop any plants which may have escaped the spraying. Roy thinks they are getting near enough to 100 percent control this way. He calls the sheep his "integrated weed managers".
Depending on the amount of ryegrass present in the paddock, Roy usually grows TT canola after the vetch to give another year of fairly good control of ryegrass using atrazine. By doing that, Roy aims to keep the seed bank down. If the ryegrass is particularly bad in the paddock, he grows vetch for another year. Legume crops are often crop-topped with gramoxone when the ryegrass is at the milky dough stage.
Cereals follow in the rotation, with one or two crops of wheat, depending on the amount of ryegrass present, followed by barley. A second barley crop is sometimes sown if ryegrass numbers are not above the threshold (50pl/m2).
Roy highlighted that adequate shedding for storage of hay was critical, and relying on contractors for baling can also be a problem. He said that vetch seems to do as well in dry years as anything else. Last year, vetch was the only thing that made money.
Ryegrass resistance to glyphosate is also another danger. Tests with glyphosate done at the Adelaide University have been showing signs of resistance developing, but at this stage it cannot be seen happening in the paddock.
The ryegrass resistance problem is becoming increasingly obvious, but Roy said that it is no worse now than it was five or ten years ago. He said mechanical methods may have to come into play more; he may have to look at cultivation and the occasional burning.
Malcolm Taylor, Robocrop project manager, introduces the Robocrop SeednWeed bar, designed for seeding, band spraying, inter-row cultivatioin and mid-row fertilisation. The Robocrop bar uses vision guidance systems to accurately position the implement in relation to an emerged crop.
When asked about making a chemical fallow in May, Roy replied that it would be using another chemical, and that 
he has a better return from hay. Harm van Rees added that in his opinion, you shouldn't need to fallow in this country (remembering Roy's place is in the Wimmera, not the Mallee).
Harm van Rees, BCG Consulting Agronomist, Cropfacts, thinks that it is still more profitable south of Charlton to grow vetch compared to fallow.
A question was asked about the nutrients taken out with vetch hay. Harm responded that while vetch is a legume and there is some benefit from with nitrogen, you lose a bit with moisture. Potassium and phosphorus are also taken out, but you're putting some back with MAP.
Roy used to grow Blanche Fleur vetch, but due to its susceptibility to rust, has swapped to Morava. He has not grown Popany, purely because it is a later variety and he can't get the hay out of the road before he wants to clean the paddocks up. Roy was growing Gungurru lupins, but has grown Myallie in the last few years. He has had no problem getting the topping done on those.
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Dr Allan Mayfield, Mayfield Consulting, explains trials investigating controlling resistant ryegrass with knockdown herbicides. In this trial, the optimum time for spraying Gramoxone as a double knock after the roundup application was a minimum of 3 days. |
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Brooke Thompson, Cropfacts, talked about some examples from this season - learning the hard way about the cost of finding out ryegrass is resistant. A plant test is a cheap way of checking for resistance status for different herbicides, compared to spending thousands of dollars on a chemical application to discover resistance the hard way. |
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Checking out the BCG resistance boom, designed to apply four different chemicals at once to enable a comparison. |
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Looking for a difference between treatments. In trials undertaken with Select and Aramo, water quality made little difference to herbicide efficacy. |