QUEENSLAND and NSW grain growers are being urged to test soil for root lesion nematode species and population ahead of summer crop planting with research showing some new crop varieties have increased susceptibility to the parasitic pest.
The research conducted by the University of Southern Queensland’s Centre for Crop Health with funding from the Grains Research Development Corporation (GRDC) examined summer crops susceptibility to specific root lesion nematode species.
USQ nematologist Kirsty Owen, who led the research, said the new data highlighted the importance of growers’ soil testing to identify nematode species, so they could select the right crop to reduce the potential impact on yields.
Dr Owen said the main nematodes found in Queensland and New South Wales arePratylenchus thornei and Pratylenchus neglectus. They are found in 77 per cent of paddocks throughout the two states with new data indicating Pratylenchus thornei is more widely distributed and found in greater, more damaging numbers than P. neglectus.
“Root lesion nematodes are a significant problem that costs northern region growers $47 million in lost wheat production annually,” Dr Owen said.
“They can reduce yields of intolerant varieties by up to 70pc in wheat and 6.5pc in chickpeas, but growers can reduce the potential yield risk by determining nematode species and selecting the most suitable crop and variety to use in their rotation.
She said most summer crop varieties are nematode-tolerant, meaning they will grow well where root lesion nematodes are present. But some varieties are susceptible and will increase nematode numbers.
“Summer crops with resistance to root lesion nematodes offer a means of reducing populations, but only when you know what species of nematodes are present,” Dr Owen said.
“Effective management of root lesion nematodes starts with growers identifying populations present in paddocks. In the northern cropping region more than 2000 nematodes per kilogram (or 2 per gram of soil) anywhere in the soil profile equates to a potentially damaging population.
“Very high nematode populations are reduced by increasing the number of resistant crops grown consecutively in rotations. It may take two or more resistant crops to reduce damaging populations, but with careful planning growers can minimise the impact of root-lesion nematodes on farm profits.”
Dr Owen said once growers knew which nematode species are present in their paddock and the population size, they could plan crop rotations to: 1. select tolerant varieties so that yields are maximised, and 2. reduce the size of the populations by growing resistant crops.
“One moderately resistant crop in a sequence is not enough to reduce damaging populations of nematodes. Growers need to plant two or more resistant crops grown consecutively to get on top of root-lesion nematodes.”
She said the new research would further help growers with summer crop selection to reduce specific nematode species and population in paddocks.
“This new research shows mungbeans are susceptible to P. thornei but are poor hosts of P. neglectus. So the take home message for mungbeans is to be aware that they will cause P. thornei to increase and should not be included in rotations where you are trying to reduce populations of P. thornei,” Dr Owen said.
“We also found that maize may not suffer yield loss due to P. thornei, but some hybrids of maize will cause populations of the nematode to build up and put the next crop at risk of attack.
“While sorghum is an excellent crop to include in rotations where P. thornei is present because it is moderately resistant. However, sorghum is susceptible to P. neglectus so growing sorghum will cause populations of P. neglectus to increase and remain in high numbers to attack the next crop.
“Our results indicate that forage sorghum hybrids are also susceptible to P. neglectuswith the sweet sorghum hybrids being most susceptible and the grain sorghum/Sudan grass-cross hybrids being moderately susceptible.”
She said the findings emphasised the importance of soil testing ahead of crop selection when it came to developing an on-farm strategy to reduce populations of specific RLN species.
She advises growers to test soil for nematodes every three to five years. PreDictaB (South Australian Research and Development Institute) offers soil tests for both species of root-lesion nematodes.
“We can’t eliminate nematodes, but if growers know the nematode species present then with strategic crop choices and the right rotations they can minimise their impact on farm profitability.”