Members of the research team collecting soil samples to test for root lesion nematode populations on a farm in Central Queensland.
PHOTO: Neil Robinson
Central Queensland (CQ) growers have usually escaped the root lesion nematode damage suffered by growers further south, but this could change if populations of the parasite increase.
Results from a survey of paddocks in CQ from 2010–13 are providing new insight into the extent of root lesion nematodes (RLN) across the northern region.
Researchers from the Queensland Department of Agriculture, Fisheries and Forestry (DAFF) and the University of Southern Queensland found that 28 per cent of the paddocks sampled had populations of RLN – mainly the species Pratylenchus thornei.
However, these populations are low in this area and the distribution is patchy compared with other areas in the north, says Queensland DAFF researcher Neil Robinson.
P. thornei is a major pest of wheat and has been known to reduce wheat yields in the northern region by 70 per cent. In the survey, however, CQ was found to have a much lower incidence of RLN, with 28 per cent of paddocks infested, compared with cropping areas such as southern Queensland, where about 83 per cent of paddocks are infested.
“The other good news is that only five per cent of the paddocks sampled in CQ had RLN populations above the wheat-damage threshold of 2000 per kilogram of soil,” Mr Robinson says.
This means CQ growers have an advantage: with preventative management of RLN populations before they increase and spread, growers may be able to prevent the RLN problem from developing to the same degree that it has elsewhere.
“Continuing to grow susceptible varieties of crops such as wheat, barley, chickpeas, mungbeans or soybeans can quickly increase the RLN population to damaging levels and help them spread across paddocks and the region,” Mr Robinson says
“Replacing these with resistant and tolerant varieties, however – such as the wheat varieties LongReach Gauntlet, Sunmate and Suntop – and rotating with tolerant crops such as sorghum, maize, sunflowers and cotton for two or more consecutive seasons, will reduce P. thornei populations.
“If you suspect that intolerant wheat varieties such as Strzelecki are underperforming, this may be an indication of an increasing RLN population in your paddock,” Mr Robinson says.
“We recommend growers test their soil for RLN every two to three years,” he says. “This will give an idea of what they are dealing with so they can develop an effective management plan.”
Mr Robinson also says it is important to practise good farm hygiene – washing soil from farm machinery and livestock – to minimise the spread of RLN between farms and paddocks.
Maurice Conway, principal technical officer at Queensland DAFF, was part of the research team that visited 39 farms over two weeks to collect samples throughout the Central Highlands region. As high RLN populations can be found below 30 centimetres in the soil profile, the survey involved taking samples as deep as 90cm.
“We sampled the main cropping soils in CQ – open downs, brigalow and alluvial on the Central Highlands – from north of Kilcummin south to Rolleston, and south-east to the Dawson and Callide valleys,” he explains.
Mr Conway says that while the RLN numbers they found were low, they were higher than he expected.
“It’s a concern that they are here in CQ and have the potential to multiply,” he says. “We didn’t find levels anywhere that would reduce yield significantly at this stage, but growers are going to have to manage RLN to keep the numbers down.”
One of the properties Mr Conway visited belongs to grower Ian Hutchings, who says the researchers were able to confirm a suspicion he’d had for some time.
“I had a difference between two different wheat varieties that I couldn’t explain,” he says. “One variety wasn’t growing as well as it usually does, and when I ran a different variety, it got better.”
The difference indicated the presence of RLN in Mr Hutchings’ soil.
Symptoms of RLN can vary depending on the level of infection and can be difficult to detect at low levels. Growers may start to notice roots that are poorly branched, lack root hairs and do not grow deeply into the soil, or plant tops that are stunted, have yellow lower leaves or wilt under water stress.
Although the RLN levels found on Mr Hutchings’ property were low, he plans to continue taking preventative measures by integrating resistant crops into his paddock rotations – growing wheat and chickpeas in the winter, and mungbeans and sorghum in the summer.
“If I’m going to grow two wheat varieties in a row, I’ll grow one that is a nematode-resistant variety one year, followed by a tolerant variety the next,” he says. “Hopefully, by doing that they won’t become a problem.”
For Queensland DAFF researcher Neil Robinson such integration is important for managing RLN populations.
“Using successive resistant crops will better serve to reduce P. thornei populations,” he says. “Mr Hutchings includes sorghum in his rotations. Sorghum is resistant to P. thornei, rotating it with susceptible crops such as wheat, chickpeas and mungbeans will help to reduce the populations in the soil.”
Following the CQ study, researchers are targeting the South Burnett region.
“We’re concentrating on regions that have been under-sampled,” Mr Robinson says. “It will be interesting to see what we find up there with crops such as maize, soybeans, wheat and peanuts.”
Results of the South Burnett survey are expected in early 2015.
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