Inter-row sowing can slow crown rot build-up
Dr Steven Simpfendorfer presented trial results showing the impact of inter-row sowing on crown rot, at the 1st International Crown Rot Workshop for Wheat Improvement
Research in New South Wales and southern Queensland has confirmed the value of inter-row sowing as part of an integrated strategy to slow the build-up of crown rot inoculum in infected paddocks.
In no-tillage cropping systems, the crown rot fungus Fusarium pseudograminearum and common root rot fungus Bipolaris sorokiniana become concentrated in rows remaining from previous winter cereal crops.
The research, by Dr Steven Simpfendorfer from the NSW Department of Primary Industries, aimed to investigate paddocks sown to wheat, barley and durum across northern NSW and southern Queensland to assess the ability of precision row placement as a strategy to reduce the incidence and severity of crown rot and common root rot in winter cereal crops.
- Trials show inter-row sowing can reduce the
incidence and severity of crown rot in cereal crops
- Inter-row sowing was less effective at reducing
the incidence and severity of common root rot
- Researcher says inter-row sowing is best used
as part of an integrated disease management system
Twenty-five wheat, 14 barley and five durum wheat paddocks were sampled at sites from Wellington in central NSW to Moonie in southern Queensland and as far west as Walgett, NSW.
Within each paddock six sampling points (one metre of plants with three samples on the previous rows and three samples in between the previous rows) were selected and marked at the tillering growth stage.
At harvest, all the plants were removed from each sampling point and the severity (according to visual symptoms) and incidence of crown rot and common root rot were determined.
The crops were sown using no-tillage into various standing winter cereal stubbles with the exception of one site, where durum residue was burnt before sowing.
Dr Simpfendorfer says the results showed that sowing between the previous cereal rows reduced the incidence of plants infected with the crown rot pathogen F. pseudograminearum by 45 per cent and the severity of disease by 51 per cent across sites and various winter cereals (Figure 1).
He says the incidence and severity of crown rot was always lower in the inter-row at all 44 sites. However, precision row placement was less effective at reducing the incidence of infection by B. sorokiniana, the cause of common root rot.
Dr Simpfendorfer says this may be because the levels of B. sorokiniana were low (less than 10 per cent) at 21 of the 44 sites.
However, at 20 of the 23 sites where moderate to high levels (10 to 50 per cent) of B. sorokiniana were measured, inter-row sowing reduced the incidence of plants infected by B. sorokiniana by 50 per cent.
At the remaining three sites the incidence of infection by B. sorokiniana was either unaffected or increased by 24 to 114 per cent in plants sown in the inter-row area.
Although inter-row sowing reduced the severity and incidence of crown rot in bread wheat, barley and durum varieties, the results showed it was slightly less effective at reducing crown rot severity in barley (average 34 per cent) compared with bread wheat (43 per cent) and durum (52 per cent) (Figure 1).
Dr Simpfendorfer says the effectiveness of inter-row sowing also appears to be influenced by the levels of crown rot within a particular paddock.
At sites where the severity of crown rot was high (more than 50 per cent), inter-row sowing reduced the disease by 29 per cent on average. In contrast, at sites with lower levels of crown rot (less than 50 per cent), inter-row sowing reduced the disease severity by 61 per cent.
Where above-ground durum residues were burnt before sowing, inter-row sowing reduced the severity of crown rot from 52 per cent to five per cent.
Dr Simpfendorfer says the higher the incidence of the crown rot fungus in previous cereal residue, the greater the chance the pathogen will move into the inter-row through fragmentation of the stubble.
He says this means the effectiveness of inter-row sowing for crown rot control is likely to be reduced over time.
“Even at lower starting levels of crown rot, inter-row sowing is likely to result in a build-up of crown rot levels over time,” he says. “It is not a solution to the disease that will allow continuous cropping of winter cereals.”
Dr Simpfendorfer says that in paddocks with low initial crown rot levels, inter-row sowing is likely to reduce the rate of pathogen build-up within a paddock by limiting the number of infected plants.
However, he explains, the value of inter-row sowing is likely to be greatest when incorporated into an integrated disease management system, which includes the use of break crops, selection of varieties with improved crown rot tolerance, grass weed control, fallow management and nitrogen management.
Evidence overturns stubble burning fix
Dr Steven Simpfendorfer of the New South Wales Department of Primary Industries says burning cereal residues is not a quick fix for reducing the crown rot pathogen, Fusarium pseudograminearum, in subsequent cereal crops.
He has tested the impact of early post-harvest burning and cultivation versus late burning (in autumn) without cultivation in a continuous wheat system in replicated trials over four seasons. The burning treatments were compared with a stubble retained no-tillage treatment.
“Burning only removes above-ground cereal residue and has no effect on the survival of the crown rot fungus in the crown tissue below the ground,” he says.
While Dr Simpfendorfer’s research showed burning stubble that is heavily infested with F. pseudograminearum did not greatly reduce the incidence and severity of crown rot in the first subsequent wheat crop because the pathogen persisted in crown tissue below the ground, repeated burning of wheat residue over four seasons led to a significant decline in crown rot levels.
An early post-harvest burn followed by cultivation was marginally more effective at reducing the incidence of crown rot infection in subsequent wheat crops than an autumn burn without soil disturbance.
Averaged across four seasons, plant-available water at sowing was reduced by about 25 millimetres with an early burn and 4mm with a late burn. Dr Simpfendorfer says this can reduce the yield benefits in the following wheat crop gained from reducing crown rot levels.
In reality, he says burning cereal residue is not the preferred option for managing crown rot because it reduces soil organic carbon levels, soil water storage and the activity of biota in the soil, as well as increasing the risk of soil erosion from wind and rain between crops.
Instead, he encourages careful selection of varieties with tolerance to crown rot, growing break crops such as field peas, chickpeas and canola, and effective grass weed control.
Dr Steven Simpfendorfer
0439 581 672
GRDC Project Code DAN00143
Region North, South