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Beyond the Bale : September 2018
ON FARM 66 RED LEAF SYNDROME Detailed guidance to help livestock producers manage the impacts of subterranean clover Red Leaf syndrome has been released, following recent outbreaks of the syndrome and associated pasture loss in Western Australia. The new fact sheet (available at www.wool.com/weeds) provides producers with a clear plan of attack if they are impacted or suspect there is Red Leaf syndrome in their clover pasture. Based on new research prompted by outbreaks in 2017, the fact sheet was produced by AWI in conjunction with Meat & Livestock Australia (MLA), the University of Western Australia (UWA) and the WA Department of Primary Industries and Regional Development (DPIRD). AWI Project Manager – Production Systems & Wool Credentials, Melissa McAulay, said that the effective collaboration between the research and development corporations and researchers was key to finding the cause of the syndrome and delivering answers and management strategies to producers. “By convening an expert panel of agronomists, researchers and producers, we have been able to identify the main cause of the syndrome as Soybean Dwarf Virus (SbDV). The research revealed that of the subterranean clover plants tested, 80% with obvious red leaves were infected with SbDV, compared to just 2% without obvious symptoms.” Given current understanding and testing of samples, researchers believe that SbDV is the most likely cause of the red leaf syndrome but it is likely that a number of other contributing stress factors are involved. SbDV is spread by aphids and frequently infects subterranean clover. Symptoms of the virus include reddening leaves, stunted plant growth and premature plant death which can lead to significant loss of dry matter and seed production. An integrated disease management approach using control measures that operate in different ways is needed to control SbDV in subterranean clover pastures: • Use insecticides only when the risk of early infection is high Application of an anti-feed insecticide (i.e. synthetic pyrethroid) at the highest registered rate for aphid control in subterranean clover at two and six weeks after seedling emergence. This will deter aphids from feeding and therefore spreading SbDV to young vulnerable sub clover seedlings. • Manipulate pasture composition Grasses do not host SbDV, so using annual ryegrass or forage oats could be a useful tactic and in the absence of an outbreak would likely improve early feed availability. • Growing alternative pasture species This is another option to lessen the impact of a loss of subterranean clover pasture as the result of an outbreak. If sowing alternative pasture species, seek further advice to see if they are suited to your soils, rainfall and management system. Serradella is an option as it does not appear to be affected by the syndrome, even when growing alongside symptomatic subterranean clover plants. However, a note of caution, it is unknown whether some of the alternative pasture species are hosts of SbDV. • Barrier Oats can be sown as a barrier around pasture paddocks to disperse aphids and slow early spread into pasture from outside sources. Ms McAulay added that if producers suspect their clover pasture is infected with SbDV, they are encouraged to send symptomatic leaf samples to the DPIRD diagnostic laboratory service for accurate diagnosis (see www.agric.wa.gov.au/ddls-plant-pathology-0) “This also enables the project team to develop a better understanding of the virus and likely causes of the disease,” Ms McAulay said. Producers are also encouraged to continue reporting incidents of the virus by engaging with the online producer survey conducted jointly by AWI and MLA at: http://survey.mla. com.au/TakeSurvey.aspx?SurveyID=clover MORE INFORMATION: The fact sheet is available at www.wool.com/weeds FAST FACTS • Research into subterranean clover Red Leaf syndrome has determined the main cause of the syndrome as Soybean Dwarf Virus (SbDV), which is spread by aphids. • To combat the risk and spread of SbDV, producers are encouraged to use a variety of control measures, including: • Use of insecticides only when the risk of early infection is high • Implementation of annual ryegrass or forage oats into pasture regimes, as grasses do not host SbDV • Consider sowing alternative legume species, such as Serradella, which do not appear to be affected by SbDV. • Producers are encouraged to read a new fact sheet available at www.wool.com/weeds. SUBTERRANEAN CLOVER An infected subterranean clover plant with red leaves. Note the reddening is from the leaf margins inwards.
In the Shops - September 2018