Crop Watch July 2020

NFNB fungicide resistance in SA update

Barley growers are advised to monitor their crops for early signs of fungicide resistance.

Recent studies have detected more cases in South Australia of resistance to succinate dehydrogenase inhibitor (SDHI) fungicide in the disease net form net blotch (NFNB). Since the first observations on Yorke Peninsula (YP) in 2019, more incidences of SDHI resistance in NFNB have been confirmed in samples from that region, and also reduced sensitivity has been observed in samples collected on the border between South Australia and Victoria, and from Eyre Peninsula (EP). Results from testing by Curtin University (CCDM) in 2019 found NFNB on YP was resistant to the SDHI seed dressing fungicide fluxapyroxad, and at the same time samples also showed resistance to the Group 3 DMI tebuconazole, which is a mixing partner in some DMI foliar fungicides.

• If you are farming in an area that has reported SDHI resistance, avoid using SDHI fungicides as further use will apply additional selection pressure, accelerate the development of resistance and potentially lead to fungicide failure
• In all other areas, if SDHI fungicides are used as a seed dressing, then follow up with a foliar fungicide with a different mode of action
• Choose fungicide mixtures with different modes of action
• Avoid planting susceptible varieties – look for diversity in varieties
• Avoid planting barley on barley
• Closely monitor crops for signs of early resistance.
• Control volunteer barley, especially those infected with NFNB – foliar fungicides in crops containing volunteer barley are likely to increase fungicide resistance in NFNB (see photo)

Additional resources

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Crop disease observations

Crops with severe ascochyta blight in lentils and some early septoria tritici blotch in wheat- be prepared to spray fungicides where necessary.

Rhizoctonia root disease and herbicide residues are affecting pulse and cereal diseases (photo below of lupin herbicide damage on roots).

Lentil

Ascochyta blight infection has been recorded on a number of PBA Hurricane XT and PBA Hallmark XT crops, some at worryingly high levels even at this early part of the season. Crops should be monitored and if disease is severe then mid-season fungicide sprays may be required to control the infection.

Wheat

Septoria tritici blotch has already been observed at low levels in a number of crops. Growers should monitor crops and prepare for fungicide applications where necessary.

Field pea

The systemic disease downy mildew has severely infected a number of seedling field pea crops around the state, encouraged by cold wet soils. No systemic foliar fungicides are registered for this disease. Primary inoculum is soil-borne and metalaxyl seed dressing is recommended in paddocks with a history of downy mildew infection.

Canola

Similarly downy mildew has been observed on canola crops (a different pathogen to the one on field pea). No fungicides are registered for this disease on canola.

Root disease and herbicide residues

The cold conditions have slowed plant growth and enhanced root infection from soil-borne pathogens, especially rhizoctonia. This disease is prevalent in both pulse and cereal crops. In some crops, herbicide residues are compounding this problem. Attached photo of lupins near Wanilla (submitted by Tim Richardson) shows signs of herbicide toxicity on the roots i.e. thickened short stubby roots. A small amount of rhizoctonia is also evident – spear tipping.