Key Points

• Yellow leaf spot can cause yield loss of up to 30% in worst-case scenarios

• Typical seasons in Dalwallinu are generally not conducive to yield loss from yellow leaf spot

• If you meet a range of risk factors; e.g. continuous wheat rotations, susceptible variety, retained stubble; it may make sense to apply a preventative foliar fungicide

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Aim

To see whether there is an economic response to foliar fungicide application to control yellow leaf spot. We also want to understand if there is value in spending more on a premium fungicide.

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Background

Yellow leaf spot is a common disease of wheat in the northern growing regions of Western Australia. Liebe R&D Coordinator Judy Storer noted that yellow leaf spot was developing on the lower leaves of the canopy at this year’s site, so an opportunity exists to test whether (a) yellow leaf spot will reduce yield in these specific set of paddock conditions, (b) whether application of a fungicide will protect yield, and (c) whether application of a premium fungicide will protect more yield than a generic fungicide.

 

The conditions most conducive to economic yield loss from yellow leaf spot are:

1. Variety susceptibility

2. Wheat on wheat rotation with retained stubble

3. 6 hours of leaf wetness at temperatures from 15-28 C

4. 100 mm rainfall post flag leaf emergence

5. Early flag leaf emergence

6. Above-average seasonal rainfall

 

In terms of what we should expect from this trial, this year has seen above-average rainfall, which is probably why we can find yellow spot in the canopy at all – there would have been plenty of extended periods of leaf wetness this season. Wheat on wheat rotation and stubble retention would also have contributed to infection – the stubble is the source of the disease. If there is no economic response from this trial, it is likely that the main contributing factors are variety susceptibility and post flag leaf emergence rainfall. Sceptre is rated MRMS for yellow leaf spot, the equivalent of 1-2 fungicide sprays better than an SVS rated variety – think Yitpi. Further, economic response to fungicide is likely when a wheat crop receives >100 mm rainfall post flag leaf emergence, which is a rarity in Dalwallinu and its surrounds.