CROWN rot disease was generally ‘well managed’ in the majority of paddocks by Queensland and NSW growers, despite it being a high risk year because of a warmer winter and a dry spring.
NSW DPI senior plant pathologist Dr Steven Simpfendorfer estimated about 30 per cent of paddocks experienced some level of whitehead expression this year, with the severity higher where rotations were more cereal-based.
“It was pleasing to drive around the region during heading and see plenty of wheat and durum crops without any whiteheads,” Dr Simpfendorfer said.
He said other crops had whiteheads at levels of around 5-10pc meaning the growers, most likely experienced crop losses of around 5-10pc due to crown rot in those paddocks.
“However this actually suggests their management was pretty good, given how conducive the season was for yield loss from this disease,” Dr Simpfendorfer said.
“This season in field trials, where we deliberately inoculated to establish high infection levels to reflect situations where crown rot is poorly managed, the losses were around 40-70pc.
“In contrast the low 5-10pc impact we saw in commercial paddocks meant growers were effectively managing the problem and minimising losses.
“So I strongly encourage growers not to lose confidence in their management strategies even if they noticed low levels of crown rot this year.”
The most effective way to reduce crown rot inoculum is to include a non–host crop into the rotation.
Dr Simpfendorfer said the wide host range and persistence of the crown rot fungus in winter cereal and grass weed residues meant it was difficult to completely eradicate from a paddock, and maintaining best practice methods to minimise infection and expression were vital.
Crown rot, caused predominantly by the fungus fusarium pseudograminearum is a significant disease of winter cereals in the northern region. Infection is characterised by a light honey-brown to dark brown discolouration of the base of infected tillers, while major yield loss from the production of whiteheads is related to moisture stress post-flowering.
“The most effective way to reduce crown rot inoculum is to include a non–host crop into the rotation, as the fungus can survive multiple years in stubble residues,” Dr Simpfendorfer said.
“Effective break crops include chickpeas, faba beans, canola and summer crops such as sorghum and mungbeans, and areas that had higher levels of loss due to crown rot this season were often in a cereal-on-cereal rotation.
“The other point is that any management strategy that limits stored soil water or creates constraints to roots being able to access this water, exacerbates the probability and often severity of moisture stress during grain-fill, which increases the impact of crown rot.”
He said crown rot expression could also be an indicator of other subsoil constraints, so any management strategy should include PreBicta B testing to identify other potential underlying issues like root lesion nematodes. A dedicated PreDicta B sampling strategy needs to be followed to ensure results are reliable.
PreDicta B, a research investment by the GRDC, is a DNA-based soil test, which detects levels of a range of cereal pathogens. It is commercially available to growers through the South Australian Research and Development Institute.
“A grower this season observed that crown rot management is like making a cake: you need to get all the ingredients right or it will be a flop,” Dr Simpfendorfer said.
“Fortunately, I see a lot of evidence of growers doing it well, and I strongly encourage those growers to keep going and not be disheartened by low levels of crown rot in some paddocks in 2017, because keeping the levels low was actually a major challenge this season.”