Ground Cover North : Ground Cover 051 August-September 2004 - North
By EMMA LEONARD As more growers adopt no-till, it is clear there are numerous different tillage implements that can be used in a single pass system including discs, knife points and even wide shears. But how do these different tillage implements affect weeds and their control? Over the past two years this question has been addressed by University of Adelaide's Drs Sam Kleemann and Gurjeet Gill. They have found some significant differences in the distribution of weed seeds, their germination and herbicide efficacy under no- till systems with different levels of soil disturbance. Three contrasting openers were used. The low-disturbance systems had disc openers (K-Hart and Day-Break), the intermediate disturbance was a 16-millimetre knife point and the full disturbance was a wide shear with a ribbon seeding boot. The trials were carried out at the Yorke Peninsula Alkaline Soils Group site at Minlaton, SA in non-wetting sand over clay. "We knew tillage influenced the vertical distribution of weed seeds however it was unclear how this related to weed germination in the paddock," explains Sam Kleemann. "We focused our assessments on annual ryegrass as this is considered to be one of the most challenging weeds to control in a no-till system." The low-disturbance disc systems resulted in more than 70 percent of the ryegrass seeds being left on the soil surface, compared to the high-disturbance full cut opener which buried 80 percent of the seeds at one to five centimetres -- leaving only 10 percent of the seed on the soil surface. Ryegrass emergence was 42 percent lower with the disc seeding (650 weeds per square metre) when compared to the full cut ribbon seeding system (1200 weeds/m2). This is a huge percentage difference in weed numbers and is considered to be of importance even when weed populations are low (50 to 150 weeds/m2). This reduction in ryegrass emergence under the disc system is considered to be due to reduced weed seed soil contact and greater numbers of ryegrass seeds being left exposed to fluctuations in temperature, insect predation and more rapid degradation on the soil surface. The intermediate and high disturbance systems resulted in a concentration of weed seeds in the nutrient-rich seedbed, an ideal position to compete with crop seeds right from the start. At this Minlaton site, about 50 percent of the ryegrass seed-bank carried over from one season to the next. Surprisingly this quantity was found to be irrespective of tillage system. The non- wetting soil characteristics of the site were considered to play a major part in this high level of carryover. In other trials in Australia, ryegrass survival from season to season has been less than 10 percent. From these results, the researchers expect to see disc seeding systems driving ryegrass populations down and full cut systems driving populations up; however the influence of soil throw and herbicide efficacy also come into play. Trifluralin is widely used for ryegrass control in no- till systems. In these trials, Trifluralin only achieved a nine percent control of ryegrass with the low- disturbance disc openers compared to 59 percent with the high disturbance system. This poor level of control is thought to be due to the lack of soil throw with the disc openers, which results in the herbicide being left on the surface where it volatilises and is degraded by light. In the coming year, Dr Kleemann will assess the efficacy of other herbicides with low-disturbance seeding systems. Disc openers may offer growers a method of minimising ryegrass germination and, eventually, the reliance on herbicides such as Trifluralin, which requires incorporation. In the meantime they may have to look to alternative herbicides such as Metolachlor. Page 24: Disc machines GRDC RESEARCH CODE UA 465, program 3 For more information: Dr Sam Kleemann, 08 8303 7908, samuel. firstname.lastname@example.org FARMING SYSTEMS 16 AUGUST 2004 TILLAGE All you need to grow • Stripe Rust • Leaf Rust • Septoria nodorum blotch • Yellow leaf spot • Septoria tritici blotch • Stem Rust • Powdery Mildew • Scald • Crown Rust • Stem Rust Wheat Barley Oats For more information: www.farmoz.com.au Head Office Telephone (02) 9431 7800 Eastern Region Office Toll Free1 800 624 597 Southern Region Office Telephone (08) 8260 0800 Western Region Office Telephone (08) 9310 5904 Orius controls the following: Broad spectrum fungicide for use on a wide range of crops Application at all disease stages Rainfast within 2 hours after application Safe to user, crop and environment Provides systemic, protective, curative and eradicant control of diseases in crop Low risk to beneficial insects Long lasting effect The star performer protecting your crop! Orius® Fungicide Seeking the truth about weeds and tillage Intermediate disturbance: tillage with knife points Single pass systems: differing tillage implements have varying impacts on controlling weeds.
Ground Cover 052 October-November 2004 - North
Ground Cover 050 June-July 2004 - North