Summary

To establish whether improving soil nutrient status can support disease resistance and tolerance in cereals, four field trials were conducted over two growing seasons. Plots were either inoculated or non-inoculated with Rhizoctonia root rot at sowing, and either treated with fungicide to control leaf disease (low disease plots) or not sprayed at all (high disease plots).

Combinations of phosphorus, copper, sulphur and potassium provided a clear yield response in the high disease treatments, possibly by providing added nutrition to affected roots. Adequate nutrition was also observed to slow the development of fungal leaf disease in some cases.

Background

Crop disease is an important constraint on yields. In-season management typically relies on in-furrow and foliar chemicals to control soil-borne and foliar diseases.

Integrated disease management strategies can minimise disease pressure, which reduces the need for chemical inputs and the attendant risk of fungicide-resistance developing in pathogen populations.

As strong and heathy plants are better able to defend themselves against disease, out-grow disease damage and maintain yields, this project aimed to explore the potential for nutrients to offset the impact of soil-borne and foliar disease in cereals.

Research Aims

The core objectives of the project were to investigate the effects of nutrition on:

• Yield under high and low disease pressure.
• Severity of root disease caused by Rhizoctonia.
• Severity of foliar diseases in cereal crop.

In The Field

Four field trials were established for this project, at sites that were potentially deficient in different combinations of phosphorus, copper, sulphur and potassium.

Plots were established under high and low disease regimes. High disease plots were inoculated with Rhizoctonia solani AG8 at sowing, and no foliar fungicides were applied in crop. Low disease plots were not inoculated and given a seed treatment plus 200ml/ha Uniform fungicide in-furrow to reduce background soilborne disease. These plots were then sprayed in-crop to manage foliar disease during the season

Various combinations of phosphorus, potassium, copper and sulphur were applied as solid fertiliser sown beneath the seed, at a range of rates, including nil nutrients, to each plot. Fertilisers were balanced for non-treatment nutrients such as nitrogen.

For the 2018 growing season, Scepter wheat was sown at Stokes and Spartacus barley sown at Wangary, both on the Eyre Peninsula. In 2019, sites were established at Coomandook in the SE and Palmer in the Murray Mallee, both sown to Planet barley, and at Kapinnie (EP) with canola.

Poor establishment and drought at Palmer resulted in poor data and no significant treatment effects, while very poor establishment at Kapinnie led to that trial being abandoned.

To assess the effects of each treatment, plants were scored for root damage and foliar leaf disease through the growing season. The crops were grown to maturity and harvested, and yield data was calculated.

Results

Copper was generally observed to improve yields under high disease pressure. Phosphorus also improved yields with a proportionally greater response under high disease pressure. Phosphorus plus copper increased yield by up to 2.31t/ha in the high disease treatment in Scepter wheat at Stokes (2018), while reducing root and foliar disease scores.

In comparison, disease alone reduced yield in Planet barley from 3.64t/ha to 3.24t/ha at Coomandook (2019), while phosphorus increased yield from 3.09t/ha to 3.57t/ha (10kg/ha P) and 3.65t/ha (20kg/ha P).

High-salt fertilisers compounded the impact of disease in some cases, such as at Stokes, where copper as copper sulphate compounded with the impact of Rhizoctonia to cause greater root damage in high disease plots. Minimising inoculum (through crop rotation) and applying fungicides remains important for disease management, however these compounding effects did not impact yield more than disease alone.

Sulphur reduced foliar disease by 9 per cent (from 27 per cent to 18 per cent) in Spartacus barley at Wangary, with minor responses also measured at Stokes. However, phosphorus and potassium had no effect on spot form net blotch at Coomandook in 2019.

The results suggest soil nutrient thresholds may be lower where root disease levels are high, and that increasing nutrient availability can help compensate for disease damaged roots.