Summary

Barley Yellow Dwarf Virus (BYDV) is a major constraint to wheat production in South Australia’s high rainfall zones (HRZ), with yield losses up to 30 per cent recorded. BYDV-PAV (Polerovirus associated virus) is one of several BYDV strains, and it’s considered the most prevalent and abundant species within the BYDV complex. Field trials conducted in 2022 and 2023 investigated the effect of insecticide regimes and varietal tolerance on BYDV-PAV incidence and wheat yield. Results showed that while insecticide applications reduced virus presence in plant tissue, the relationship with grain yield was inconsistent and confounded by environmental variables. Effective virus management in the HRZ will require combining resistant varieties, strategic aphicide use, and better virus detection tools for informed in-season decisions.

Background

BYDV is a serious yield-limiting disease in wheat, particularly in South Australia’s HRZ, where prolonged aphid activity increases infection risk. Historically, BYDV has caused significant crop losses, up to 30 per cent. While some wheat varieties have shown tolerance, effective management strategies combining genetics and agronomy are still being refined. Growers are increasingly sowing slower-developing winter wheats in these regions, but the optimal use of insecticide treatments for these varieties remains unclear. Greater understanding of BYDV strains, symptom expression, and vector dynamics is required to refine management practices and reduce yield gaps in HRZ farming systems.

Research Aims

The core objectives of the project were to:

• Identify agronomic tactics and insecticide regimes to minimise the incidence of BYDV in selected wheat varieties in the HRZ.
• Evaluate the value of BYDV tolerance in HRZ wheat crops using BYDV tolerant and non-tolerant cultivars.
• Monitor the effectiveness of insecticides, seed dressings and in-crop applications, and timings in managing BYDV in selected wheat varieties.
• Determine differences in wheat grain yields and quality with different agronomic tactics and insecticide regimes.

In The Field

Field trials were established in 2022 and 2023 at Conmurra and Struan Farm, respectively, in the Limestone Coast HRZ of South Australia. Trials included multiple winter wheat varieties and insecticide management regimes. Insecticide regimes included untreated controls, seed dressings, and combinations of seed dressings with in-crop foliar sprays.

Aphids inoculated with BYDV-PAV were released at the trials. Visual assessments were conducted throughout the growing season to identify typical BYDV-PAV symptoms. Tissue samples from trial plots were collected and analysed to detect the presence of BYDV-PAV strains. The trials aimed to measure both grain yield and quality in relation to virus incidence and treatment application.

Results

In 2022, despite inoculated aphid releases, BYDV-PAV was not detected at the site, likely due to natural predators and cold weather limiting aphid activity. However, insecticide applications improved yields in susceptible varieties. BYDV-susceptible variety RGT Accroc yields increased by 13.5 per cent when seed dressing and three in-crop foliar sprays were applied compared to untreated controls. BYDV-tolerant variety Manning showed limited yield response to insecticide application.

Despite the finding that BYDV was not detected, visual assessments, based on the GRDC factsheet on BYDV, had identified ‘typical’ BYDV symptoms, raising questions about the ability to visually identify BYDV in-crop to make insecticide decisions.

In 2023, virus inoculation was more successful, and BYDV-PAV was confirmed in stem samples. The level of infection differed significantly between insecticide treatments, with untreated plots showing the highest infection rates at 60 per cent. While stem infection levels varied by variety, there was no direct correlation between infection levels and grain yield, suggesting other factors were influencing yield. Nevertheless, insecticide treatments reduced virus infection rates, and some varieties such as RockStar and Manning showed lower infection overall. Grain quality parameters also varied slightly among treatments.