Yellow leaf spot (YLS) of wheat has become more prevalent during the last 20 years due to the widespread adoption of cultivars that are YLS susceptible, the intensification of wheat in the cropping system (made possible due to CCN resistant cereals) and the adoption of stubble retention. Even though this disease is widespread, its effect on grain yield and quality is unclear. Some believe that it is predominantly a disease of seedlings and causes negligible loss to mature crops, while others regard yellow spot as an important disease and apply fungicides for control. Fungicides often only provide partial yellow leaf spot control and are not always economic.
Measuring yield loss in wheat due to YLS is complex. Traditionally, yield loss due to foliar diseases is measured by comparing the grain yield of plots treated with and without foliar fungicides. However, this also provides differential control of stripe rust and fungicides often only provide partial control of YLS. A possible solution is to compare the relative yield of wheat cultivars with different resistance/ susceptibility to yellow leaf spot in the presence and absence of yellow spot inoculum and by controlling rust through the use of flutriafol treated fertiliser at sowing.
TAKE HOME MESSAGES
- Yellow leaf spot reduced grain yield in susceptible wheat cultivars by eight per cent.
- When sowing into paddocks with yellow leaf spot infected wheat stubble, farmers should consider growing resistant cultivars in preference to susceptible cultivars.
AIM
To determine the yield loss caused by YLS in wheat in the Victorian Mallee.
TRIAL DETAILS
Location: Quambatook
Soil type: Clay loam without sub-soil constraints
GSR (Apr-Oct): 168mm
Sowing date: 7 May
Seeding equipment: Knife points, press wheels, 30cm row spacing
Target plant density: 130 plants/m²
Crop type: Wheat (Refer to Table 1)
Harvest date: 14 November
Trial average yield: 2.2t/ha
TRIAL INPUTS
Fertiliser: Granulock Supreme Z treated with Intake Hi-load Gold @ 50kg/ha at sowing; urea @ 90kg/ha applied GS21 (June 19) and GS31 (July 18)
Herbicide:
Pre-sowing Trifluralin @ 2L/ha + Avadex® Xtra @ 2L/ha
In-crop Velocity® @ 670ml/ha + 1% v/v Hasten (June 10); Crusader™ @ 500ml/ha + Chemwet 1000 25% v/v (August 14)
No fungicides or insecticides were applied.
METHOD
Wheat cultivars with various resistance/susceptibility to YLS (Table 1) were sown in the field at Quambatook in the presence and absence of YLS infected wheat stubble. The untreated plots had barley stubble applied to ensure all plots were treated equally. The trial was sown with six replicates using a complete randomised split-plot design. Wheat plots were separated by two plots of barley (~4m) to reduce inter-plot spread of inoculum from treated to untreated plots.
Plots were assessed for YLS severity and stripe rust development, and harvested for grain yield.
RESULTS AND INTERPRETATION
Yellow leaf spot was more severe in susceptible than in resistant varieties and in those plots with infected wheat stubble than those with uninfected barley stubble (Table 2). Even though there was a good establishment of YLS early in the season, the disease did not progress well during the dry spring, limiting the potential for further disease development and effects on grain yield.
Grain yield is shown in Table 3. Even though the data did not show significant yield loss at the conventional 5% probability there was a suggestion of a higher yield loss in the susceptible cultivars than in the resistant cultivars (P=0.098). Therefore the analysis was repeated by grouping the resistant and susceptible cultivars, which showed a significant (P=0.023) yield loss in the susceptible cultivars of 8% (Table 4). This finding was similar to the 8% yield loss measured in susceptible cultivars at Quambatook during 2013.
COMMERCIAL PRACTICE
This trial indicates that yield loss due to YLS is greater in susceptible than resistant cultivars. When planting in paddocks with infected wheat stubble, growers should consider using resistant cultivars in preference to susceptible cultivars when possible.
ON-FARM PROFITABILITY
In paddocks with infected wheat stubble present there is approximately a 5 to 10 per cent yield advantage in selecting YLS resistant cultivars over susceptible cultivars. This trial yielded an average of 2.2t/ha, meaning return from resistant varieties would be $29 – $57 higher than from susceptible varieties. (based on APW1 wheat price at Quambatook on 25 November 2014).
ACKNOWLEDGEMENTS
This trial was funded by GRDC through the ‘Improving grower surveillance, management, epidemiology knowledge and tools to manage crop disease in Victoria’ project (DAV00129) and the Victorian Government.
