Ground Cover South : Ground Cover 057 August-September 2005 - South
Herbicide resistance 21 AUGUST/SEPTEMBER 2005 GROUND COVER CONTROL Options for resistant ryegrass There are 23 cases of glyphosate-resistant annual ryegrass in broadacre cropping in Australia. Common factors such as intensive glyphosate use and lack of tillage have been associated with all cases. Non-chemical controls including increasing tillage are considered ways of decreasing the risk of developing glyphosate resistance. Another is the use of the double knock. Before seeding, the use of the double knock --- an application of glyphosate, which is in Group M, followed by an application of a paraquat-based product, Group L --- within a week unless otherwise advised, helps provide rapid control of glyphosate-resistant weeds. Researchers say both herbicides should be used at the full label rate. Modelling by WAHRI has shown that a long-term double knock strategy can extend the life of glyphosate by 20 years or more, by making it highly unlikely that any glyphosate-resistant ryegrass will set seed. Trials by Syngenta also show a 10 to 15 per cent improvement in weed control using the double knock compared to a single application of glyphosate or SPRAY. SEED® and a 150 kilogram per hectare yield advantage. What is driving herbicide resistance? n No-till farming has been adopted at a dramatic rate, and the trend is predicted to continue. However, in a survey of 384 growers from the western and southern regions by the Cooperative Research Centre (CRC) for Australian Weed Management, 38 per cent of those using no-till indicated they had reduced or were planning to reduce its use over the next five years. The main reason given was concern about weed control, including herbicide resistance. So should growers be turning away from no-till because of weed control and herbicide resistance concerns? The adoption of no-till has seen the direct substitution of weed control by tillage with weed control by herbicides. This approach to weed control is probably the greatest threat to the viability of no-till, as research has shown that over- reliance on the same herbicide groups causes resistance to develop -- not the removal of tillage from the system. Cases of herbicide resistance were reported on broadacre cropping farms in Australia before no-till was adopted. However, with no-till, reliance on herbicides has increased. The survey by Mechelle Owen and Michael Walsh from the WA Herbicide Resistance Institute (WAHRI) evaluated the level of herbicide resistance in annual ryegrass, (Lolium rigidum) in 503 randomly selected cropping practices, in 15 agronomic regions. Very high frequencies of resistance to the Group B (ALS-inhibiting) and Group A (ACCASE-inhibiting) herbicides were recorded. For example, 88 per cent of annual ryegrass populations were resistant, or developing resistance, to Group B sulphonyl urea herbicides. Sixty-seven per cent of the populations were resistant or developing resistance to the Group A herbicide diclofop and 24 percent were developing resistance to Trifluralin, Group D. Only six per cent of weed populations were susceptible to all the herbicides tested. Indeed, 64 per cent of the populations were not killed by either Group A (fop) or Group B herbicides. "In the past five years, the two surveys, conducted in the same regions, have shown a 21 per cent increase in the incidence of annual ryegrass populations with resistance to diclofop and a 24 per cent increase in those with resistance to sulphonyl urea herbicides," Ms Owen says. The survey did not report the relationship between tillage system and resistance, but did note that more resistant populations were found in the medium- and high-rainfall areas in WA's central and northern regions. "This is most likely to be due to longer intensive cropping histories and therefore greater herbicide selection pressure," Ms Owen explains. Although only six per cent of populations could be controlled by all herbicides tested, one ray of light was that some key herbicides such as clethodim (Select®) remained effective on most populations. There are now signs that a rapid increase in resistance to this herbicide is on the way. Researchers say weed control may no longer be a simple case of spraying, and that viable weed control will require tactical management to deplete weed seed reserves. Techniques such as grazing, burning and autumn tickle improved the kill at seeding using the double knock, although leading international no-till specialists such as Paraguay's Rolf Derpsch say any reduction in soil cover will only make the problem worse. Nonetheless, current advice in Australia is that targeting weed seed at maturity using crop topping, hay crops and seed catchers at harvest, all play a part in KEY POINTS n Survey data from WA shows that herbicide resistance populations are increasing n The link between herbicide resistance and no- till is not direct n Using the double knock is helping to improve control of resistant ryegrass n Viable weed control will require tactical management to deplete weed seed reserves Researcher Mechelle Owen: 88 per cent of annual ryegrass populations surveyed in WA were resistant or developing resistance to Group B herbicides. TRITICALE TO THE FORE n With some markets moving away from direct consumption of grains towards 'indirect consumption' (drinking milk and eating meat from animals that eat grain), the GRDC has for some time recognised that the world demand for quality feed grain is going to rise. This has important implications for Australian growers, so the GRDC is investing in the development of better feed grain varieties. One of these is triticale, the versatile hybrid of wheat and rye. Triticale has several advantages in Australian conditions -- it is a relatively low- input cereal crop with good disease resistance, particularly to rusts. It is as high a quality feed grain as wheat and is a hardy plant. Jason Reinheimer, triticale breeder with Australian Grain Technologies (AGT), says triticale is expected to play an important role in intensive cropping systems in the future, and new varieties are being bred in anticipation of the rising demand for quality feed grain. AGT, a partnership between the GRDC, the University of Adelaide and South Australian Research and Development Institute (SARDI), is one of a number of organisations researching triticale. AGT has inherited triticale germplasm developed by the University of Adelaide and CIMMYT, the International Maize and Wheat Improvement Centre in Mexico. Mr Reinheimer is gathering more material from countries such as Germany and Poland where triticale is widely grown. Mr Reinheimer says European triticale lines often experience high disease pressure, while the CIMMYT lines have been developed more with soil toxicity, drought and frost in mind. There is a lot of diversity in triticale out there, and he aims to breed the best characteristics into varieties that Australian growers will be seeing in the next few years. One promising line -- TSA0015 -- could be ready by 2007. It is high-yielding, adaptable to low- and high-rainfall areas, and enjoys robust resistance to rusts, high hectolitre weights and low screenings. It has been tested in the field at 15 sites across the southern cropping belt and in WA. Other varieties that also feature resistance to cereal cyst nematode (CCN) are expected to emerge from the program from 2008. The overall aim of the program is to provide growers with a quality feed grain that can be used more profitably in a range of cropping systems. ∆GRDC Research Code AGP00005 For more information: Jason Reinheimer, 08 8303 7707 successful weed control in no-till systems. These tactics are explored in the Integrated Weed Management Manual, which will be released by the CRC for Australian Weed Management in the spring. ∆GRDC Research Code UWA399 For more information: www.weeds.crc.org.au/glyphosate. WAHRI: firstname.lastname@example.org Emma Leonard reports on concerns of herbicide-resistance researchers that no-till cropping is being blamed for the increase in herbicide resistance, without any supporting evidence Emerging role: AGT's Jason Reinheimer inspects another promising triticale line in the AGT greenhouse at Roseworthy.
Ground Cover 058 October-November 2005 - South
Ground Cover 056 June-July 2005 - South