Summary
Soilborne root disease has long been suspected to be the main cause of poor productivity and lack of persistence of subterranean clover pastures across southern Australia. Tests across south-west, southern and south-east Australia – home to 29 million hectares of sub-clover pasture – found almost all samples suffered root disease. More than 80% of samples suffered extreme levels of disease. After an initial three years of glasshouse and plot trials, during 2015 and 2016 research moved to large-scale field trials carried out at 16 field trial sites (two in each state each year — WA, SA, Vic, NSW). In summary, the most cost-effective on-farm chemical treatments and cultural practices for control of root disease in sub-clover pastures include: (i), soil cultivation to reduce pathogens and subsequent root disease impact on productivity for several years; (ii), when registered, fungicide seed coating prior to replanting, or fungicide sprays on regenerated pastures, particularly fungicides that boost plant immunity; (iii), improving soil and plant nutrition to enable better root and shoot growth even when disease is severe; (iv), choosing varieties that perform best in your area; (v), sowing a mixture of clovers can be a good insurance policy; and, (vi), use a rotational grazing system that allows more plant growth that in turn improves root development even where disease is severe.
While no silver bullet was discovered to cure soil-borne diseases, the research reinforced that long-term success will rely on identifying resistant and field-tolerant sub-clover varieties – which is likely to boost productivity up to 4–5 fold. In the interim, focussing on pasture health first and foremost is the best approach — healthy plants best tolerate disease. To this end, this project has identified a range of flexible management options producers can employ to minimise the impact while they wait for resistant varieties to be delivered to market. In addition, producers now have access to rapid diagnostic testing through the Predicta B test to help producers establish the main causes of root disease on their property and support strategic management decisions. Overall outcomes for producers from this project, across southern Australia for farming systems involving sub-clover pastures, include: availability of effective, practical and flexible chemical and cultural options to reduce the losses during autumn-winter from soil-borne root disease; availability of meaningful Predicta-B tests to predict pathogens and their incidence; knowledge of true losses from soilborne pathogens; and an understanding of the influence of environmental factors on root disease epidemics. It is clear from these studies that while locating and developing further improved host resistance offers the best long-term and most cost-effective way to curtail future losses from damping-off and root disease occurring in subterranean clover, this critical benefit for meat and other livestock producers will only occur if there is new funding support for such an approach to be delivered.
Pathology skills and expertise have been greatly enhanced and consolidated, particularly in relation to the technical and knowledge capacity on pasture plant pathology - soil biology. This skills have now been secured for current and, providing there is ongoing industry support, future pathology requirements of the livestock industry.
