BIGG - Soil borne diseases of sub-clover

Summary

​Subterranean clover is the dominant pasture legume of grazing systems throughout the Barossa region in South Australia. In 2014-2017 the Barossa Improved Grazing Group conducted a MLA Producer Site Research Project to determine the effect of soil borne root diseases on sub-clover. Various small-plot field experiments were undertaken that focussed on evaluating strategies to reduce root disease impact and improve sub-clover winter productivity. These management strategies included the use of fungicides, inoculants and fertilisers.

In the fungicide experiments, fungicide application had no affect on dry matter production of the sub-clover varieties, Clare and Trikkala. This included the treatments registered for use in sub-clover, Metalaxyl (Apron®XL) seed treatment and Phosphorous acid (Agri-Fos® 600) foliar treatment. The lack of a positive response to fungicide application also suggests that Clare and Trikkala can perform well in the presence of root diseases.

In the inoculant experiments, the Group C inoculants, Nodulaid® (peat inoculant) and Alosca (granular inoculant) were applied to sub-clover plants at the cotyledon stage. This was conducted to determine their potential use in regenerated pastures, however neither were found to improve sub-clover dry matter production or plant nodulation.

In the fertiliser experiments, up to five treatments (Superphosphate, Complete Fertiliser, Superphosphate+DAP, Urea and Sulphate of Ammonia) were evaluated across four trials. Superphosphate and or Complete Fertiliser significantly improved sub-clover dry matter production in winter/early spring by 28-112% at the sites with marginal soil phosphorus levels (<21 mg kg colwell). These results emphasise the importance for producers to know the soil nutrition status of their paddocks and the benefit of maintaining soil nutrients (particularly phosphorous) at adequate levels, irrespective of the presence of root diseases.>

In addition to the experiments, there was a strong focus on extension and communication activities throughout the project. This included conducting six ‘pasture walks’ and delivering 20 articles for local, state and MLA media.

The projects results indicate that the management of soil borne root diseases for sub-clover is difficult. Root diseases in pastures usually occur as complexes of two to four key pathogens (Pythium, Phytophthora, Rhizoctonia, Aphanomyces) with the severity of each being expressed under different environmental conditions. There are also no fungicides registered for use in sub-clover that are effective on all diseases, hence sub-clover variety selection is critical when sowing a new pasture.</21>