Australia
May 6, 2013
Yellow spot spores over-summer on wheat spores and the disease is not well managed by fungicides
Crop rotation is the key to yellow spot management with winter cereal growers urged to make crucial decisions prior to planting to minimise the risk of incursions.
Dr Steven Simpfendorfer says the best strategy is to avoid sowing wheat-on-wheat as spores over-summer on cereal stubble.
“Unlike stripe rust, fungicides are a poor last resort for controlling yellow spot as they have reduced efficacy,” he said.
“It’s best to avoid wheat-on-wheat but if you are committed to that crop sequence, consider a late stubble burn in autumn and select a wheat variety with some level of resistance to yellow spot,” he said.
“Growers should also consider tolerance and resistance ratings for other major diseases such as stripe rust when choosing varieties.”
Dr Simpfendorfer says Grains Research and Development Corporation (GRDC)-funded research carried out by the Northern Grower Alliance (NGA) and Grains Orana Alliance (GOA) shows early fungicides on seedlings are not economical for yellow spot control.
“All fungicides have very limited kick-back activity against yellow spot,” he said.
“Recent German data demonstrates that the main fungicides (and a huge range of experimental actives) only provide between zero and two days kick-back activity.
“None of the up-front, seed or in-furrow fungicides have activity against early yellow spot infections.”
He says yellow spot is commonly a problem in wheat-on-wheat situations at seedling growth stages (emergence through tillering) in the northern region when susceptible varieties are grown such as EGA Gregory or Spitfire .
“It is less common that yellow spot progresses into the upper canopy to affect the top three leaves which are the main contributors to grain yield as this requires frequent (often prolonged) rain fall events during the season.
“Yellow spot is frequently misdiagnosed within industry so if you think you have yellow spot or have been advised that you have yellow spot and need to spray a fungicide do some very simple checks first.
Dr Simpfendorfer recommends answering these questions to identify the disease:
- • Is there wheat stubble visible in the paddock? If wheat stubble is still visible then yellow spot inoculum may also still be present.
- • Are black fruiting bodies visible on the stubble? By autumn/winter black, pinhead sized, raised structures with hair-like projections (makes them feel rough if rubbed with finger) will be visible on wheat stubble.
- • Do the lesions or spots look right? Initially small brown spots with discrete yellow margins which with age become more elongated and tan (dead dried leaf tissue) still with very tight yellow (toxin production) margin. Yellow spot does not cause extensive general yellowing of leaves.
- • Is the distribution both on individual leaves and within leaves on a tiller right? Yellow spot spores land randomly on individual wheat leaves and just require adequate moisture for more than six hours to germinate and infect. Symptoms are randomly distributed across an individual leaf and yellow spot does not concentrate towards the leaf tip.
To download a GRDC fact sheet on yellow spot, visit http://www.grdc.com.au/GRDC-FS-YellowSpotNorth. For more information on GRDC-supported research, visit www.grdc.com.au.
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