The headers that rolled across grain paddocks in Queensland and northern NSW last season didn't only help restore growers' bank balances; they provided further proof that root lesion nematode (Pratylenchus thornei) is well established in the region. John Thompson leads a Queensland Wheat Research Institute (QWRI) pathology team which has been testing grain varieties on land severely infested with nematodes following wheat crops the previous year.
"Damage from root lesion nematodes is very evident in many wheat crops in 1996," Dr Thompson said.
"They range from very large areas of some paddocks on the Darling Downs and northern NSW to smaller patches in some paddocks of the south-west Downs." The research — carried out under the GRDC's Northern Wheat Improvement Program — has allowed the team to rank wheat and barley varieties in terms of their tolerance of root lesion nematode. According to Dr Thompson, farmers with nematode-infested paddocks who want to stay with winter cereals in 1997 should consider the relative tolerance of varieties to sow.
How to minimise yield losses
"Yield losses in affected areas were estimated at more than 50 per cent for intolerant varieties like Batavia, yet our research shows much less damage to the varieties with the highest level of nematode tolerance, Sunvale and Pelsart.
"In yield tests over two years, these varieties averaged 4.1 t/ha on nematode-infested land, and one of them should be selected where nematodes are well entrenched in a paddock.
"Pelsart also has a useful level of resistance to crown rot, and would be the variety of choice if both diseases are present."
Dr Thompson says the variety choice is wider where nematodes are known to be present but not considered to be well established across a whole paddock. QWRI's yield tests showed varieties with high tolerance averaged 3.2 t/ha on nematode-infested land.
Growers seeking to manage nematode problems could also look to the durum wheats Yallaroi (very high tolerance) and Kamilaroi (high tolerance) or to planting barley, where most varieties have a very high tolerance.
"Durum and barley varieties also have better resistance to P. thornei than bread wheats," Dr Thompson said. "Resistance means that nematodes will multiply more slowly in their roots than in bread wheats, leaving fewer nematodes in the soil to attack following host crops like wheat, chickpea or mungbean."
Dr Thompson said farmers disappointed in their crop performance in the current season could still have the extent of nematode infestation diagnosed, because the organism remained in the soil after harvest. He said soil samples should be taken from the 0-15 and 15-30 cm layers of affected areas and sent to the Soil Microbiology Section, QWRI, for diagnosis, preferably with a prior telephone call to 076 398 888.