Root lesion nematodes might be out of sight for most northern grain growers but their potential impact on crop productivity and profitability is far from out of mind.
Research funded by the Grains Research and Development Corporation (GRDC) is not only quantifying how serious the production implications can be but also how long it takes to reduce damaging populations of the root lesion nematode Pratylenchus thornei (P. thornei) in the soil.
The research involves a combined project between CSIRO and the University of Southern Queensland (USQ) which draws on the historical research of Professor John Thompson.
P. thornei is a major pest of cereal and pulse crops on the heavy clay textured soils of the northern grains region and has a broad host range covering many cereal and pulse crops.
In Australia, yield losses in intolerant wheat varieties as a result of P. thornei have been estimated at between 44% and 80%, resulting in an estimated annual cost to the industry of around $38 million.
In the northern cropping region, P. thornei at ~2 nematodes/g soil (equivalent to 2000/kg soil) anywhere in the soil profile is considered a damaging population.
Recent trial work has demonstrated that fallowing or the use of consecutive non-host crops such as sorghum has the potential to significantly reduce P. thornei populations.
However, CSIRO senior research scientist Dr Jeremy Whish said population reduction can take a long time and the pests may never be completely eliminated, with trial data showing low numbers of P. thornei still present in soils fallowed continuously for eight years.
“High populations of 80 nematodes per cubic cm (~80,000 P. thornei/kg) took four years to reduce below the threshold. This would require two non-host crops such as sorghum and fallows to reduce the population,” Dr Whish said.
“A moderate initial population of 50 nematodes per cubic cm (~50,000 P. thornei/kg) took three and a half years to reduce below the threshold, requiring the equivalent of a single non-host summer crop and fallows.
“A population of 20 nematodes per cubic cm (~20,000 P. thornei/kg) took 24 months.”
He said the trials had highlighted the long survival mechanisms of root-lesion nematodes, making it critically important for growers to be aware of a soil’s P. thornei population size at the end of each season and prior to planting.
“Once a population increases, the only way to reduce the population below the damage threshold is to incorporate non-host, resistant crops or fallows,” Dr Whish said.
“Planting susceptible or tolerant crops within this time period will increase populations to higher levels that will take even longer to reduce, thereby limiting cropping options and potentially reducing the profitability of the overall farming system.
“The other important point to remember is that weeds can be a host so fallows must be weed free and free of volunteers.”
The DNA-based soil testing service PreDicta B® offered through the South Australian Research and Development Institute (SARDI) provides an indicator of root lesion nematode populations for growers and should be used prior to planting to establish whether crops are at risk and if alternative crop types or varieties should be grown.
Soil sampling for a PreDicta B® test to determine RLN levels can be arranged by contacting commercial testing service, Crown Analytical Services, which provides northern growers and advisors with bags, soil corers, protocols and procedures for sampling as well as an interpretation of results once tests are completed.
07 4688 1419
Sarah Jeffrey, Senior Consultant Cox Inall Communications
0418 152 859