STUBBLE borne diseases were most common in Western Australian crops last year and will continue to be an issue for 2022.
Last year, the Department of Primary Industries and Regional Development (DPIRD) conducted a spring surveillance program of 230 paddocks to check for the incidence and severity of diseases across the State.
While stubble borne diseases were the most common, that does not necessarily mean they were the most damaging.
In barley, spot form net blotch (SFNB) was again the most prevalent disease, having been found in 78 per cent of paddocks surveyed and in the Kwinana zone, every paddock was infected.
DPIRD senior research scientist Geoff Thomas said the level of SFNB infection was not surprising given the susceptibility of varieties to the disease and the commonality, particularly within that Kwinana zone, of barley on barley.
"We might expect that to change a little over time as our variety spectrum changes to varieties with slightly improved resistance, but for now SFNB will still need to be monitored and controlled," Mr Thomas said.
The other stubble borne disease which was established in barley, mainly in the southern regions, was net form net blotch (NFNB), with 36pc of paddocks Statewide and 100pc of paddocks in Albany and Esperance affected.
One explanation was the emergence and establishment of the Oxford pathotype of NFNB and the high susceptibility particularly of Planet to that pathotype.
"Planet is fairly dominant in those southern regions so it's no surprise that we're seeing NFNB establishing itself as a disease needing management in that zone," Mr Thomas said.
"We would suggest it would continue to be an issue while Planet dominates the landscape."
With both NFNB and SFNB, there are issues associated with reduced sensitivity or resistance to DMI fungicides, while with SFNB there is a significant concern around mutations for reduced sensitivity or resistance to SDHI fungicides.
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For wheat, yellow spot and nodorum blotch were the main stubble borne diseases of note last year, with 93pc of paddocks affected.
However, generally speaking the infection was at a lower severity as the variety spectrum is on the better end for those diseases, so while the disease is present, it's not as damaging.
While not a stubble borne disease, scelerotinia was common in canola and lupins, with about 50pc of canola paddocks having infection and 40pc of lupin paddocks.
North of the Great Eastern Highway was the area of greatest impact and in Geraldton 100pc of canola paddocks and 45pc of lupin paddocks surveyed had some degree of sclerotinia infection.
Blackleg was also an issue with 41-46pc of paddocks impacted by either stem canker or upper canopy infection (UCI) and Mr Thomas expects it to be an ongoing issue this season.
"The canola area last year increased by about 25pc so we know there is going to be more canola stubble out there and this year there is no indication the area of canola has reduced," he said.
"As blackleg is a stubble borne disease, we're facing a circumstance where canola crops this year are likely to be closer to stubble from last year.
"Earlier sown crops are likely to have great exposure to UCI, while if spores are released from stubble and come across a crop at seedling stage, then that's the situation that predisposes a crop to greater risk of crown canker."
For oats, septoria avenae blotch was most common with 97pc of paddocks affected and the most damage seen in the high rainfall western region of the Kwinana zone.
However, of more concern for DPIRD was the first recorded confirmation of red leather leaf disease - a seed and stubble borne fungal disease which is favoured by damp and cool winter conditions.
Three positive samples were discovered last season, coming from the high oat inclusion region around Narrogin, Pingelly and Piesseville.
"We don't really know what the implications are for WA, but in Victoria red leather leaf is the most common and damaging disease of oats in the south east of the State," Mr Thomas said.
"Ninety per cent of the high rainfall zone in Victoria was infected, causing 5-13pc yield loss for grain and 7-13pc for hay."
Overall, widespread rainfall since April has provided some significant early sowing opportunities across the State and for this season, that will have implications for sowing time of crops, maturation of spores on stubble and development of early volunteer regrowth.
