Ground Cover Supplement : GC Supplement - Summer weeds
17 Issue 137 | Nov – Dec 2018 | GRDC GROUNDCOVER SUPPLEMENT: SUMMER WEEDS GROUNDCOVER SUMMER CROPS / MRLs FAST FACT Sowing sorghum and mungbean crops at high density and in narrow row spacings can reduce summer grass weed biomass and seed production. PHOTO:ADAMMCKIERNAN,QUEENSLANDDAF COMPETITION However, by planting the crop at the higher density or with a narrower row spacing we were able to reduce both the weed biomass and seed head production (measured just prior to harvest) for both grass weeds. The seed head data is presented in Figure 1. Crop competition is a useful weed- control tactic which, in combination with other weed-control tactics such as herbicides, can improve in-crop weed control and provide positive crop yield gains. Mungbean yields also improved with narrow row spacing and increased density. While sorghum yields improved with increased density, there were yield penalties with narrow row spacing. Over the next three years this research will explore the impact of variety choice, precision planting and fertiliser placement on competitiveness of sorghum, mungbeans, chickpeas and faba beans. The project will also investigate the impact of a competitive wheat crop on spring-emerging summer weeds, including summer grasses, fleabane and common sowthistle. o OFF-LABEL HERBICIDE USE NOT THE SOLUTION TO SUMMER WEEDS By Gordon Cumming GRDC Manager Chemical Regulation n Hot conditions and moisture stress make controlling summer weeds a tough challenge. It may be tempting to use higher rates than stated in the label recommendations, but off-label use of chemicals can result in growers exceeding maximum residue limits (MRLs) in marketable produce including grain, forage and animal products. If Australia’s produce is found to have exceeded an MRL, the reputation of our entire agricultural industry will suffer. This will mean additional cost imposed on exporters through higher residue testing at grain receivals by importing nations, and increased on-far m audits. Repeated violations are likely to lead to chemicals being removed from the market. It is essential that growers use only registered products and observe all label recommendations including application timing, maximum rates and withholding periods. It may not be top of mind, but off-target spray drift is another potential cause of MRL breaches. Spray drift, when spraying a crop or fallow, can result in detectable MRLs in grain, forage and even animal products through grazing of affected pastures. It is the responsibility of all operators to ensure that chemical trespass (drift) does not result from your crop protection activities. Grain and produce samples are tested for pesticide residues in Australia and when export shipments leave the port to ensure they are within MRL limits. Australian MRLs are set by the Australian Pesticides and Veterinary Medicines Authority (APVMA) as part of the registration process at levels that pose no risk to human health and are not likely to be exceeded if used in accordance with the directions for use on the product label. All growers need to abide by the product label directions for use to protect Australia’s status as a producer of ‘clean and green’ produce, maintaining our commercial advantage. Any violations will affect the marketability of Australian export commodities impacting on all growers. Controlling weeds while they are still small, after rain when they are less stressed and using label recommended additives are better options for improving summer weed control. o More information: Gordon Cumming, 0428 637 642, gordon. firstname.lastname@example.org GRDC Research Code US00084 More information: Dr Michael Widderick, Queensland DAF, 07 4529 1325, michael. email@example.com; https://grdc. com.au/resources-and-publications/grdc- update-papers/tab-content/grdc-update- papers/2018/03/deprive-weeds-of-sunlight-and- space-crop-competition-research; www.grdc.com.au/GRDC-FS-GroupAinFallow Awnless barnyard grass in mungbeans.
GC Supplement - Stubble