Fight nematodes with crop choice

Common across much of northern NSW’s cropping belt, the high levels of Pratylenchus thornei (Pt) have been detected by Crown Analytical Services at Moree, using its Predicta B soil test, which also includes a crown rot stubble test.

RLN are microscopic worms in soil that live inside plant roots and are present in about 70 per cent of Australia’s northern region cropping belt.

Test results from the past three seasons show about 50pc of paddocks are in a low range for nematode populations; 25pc are in a moderate range, with potential to have some yield loss; and the remaining 25pc are in a high to very high risk range.

Narrabri agronomist Drew Penberthy, Penagcon, said while the risk of nematodes depended on crop rotation, the dry season had prompted more farmers to test soils before planting.

Pt is the prominent nematode in northern NSW, but there have been high populations of Pratylenchus neglectus (Pn) found in the Croppa Creek area, Mr Penberthy said.

“Because we’re struggling with soil moisture and nitrogen is down, we could run into some real issues this year,” Mr Penberthy said.

“With the drier start to the season, growers are worried about crown rot so it’s prompted more people to take the test.

“Numbers probably haven’t changed too much in the past three years, but because we have less moisture for that crop to respond to any damage to the root system, we’re looking at potentially higher yield losses.

“We’ve also had more growers come on board in the past few years as the testing has taken off.”

Tests have influenced growers’ decisions on crop rotation and varieties.

Wheat, faba beans and chickpeas leave significantly higher nematode levels in the soil than cotton, sorghum and canola.

The biggest risk to yield loss is high nematode levels and crown rot issues together, Mr Penberthy said.

“Crop rotation is the best way to manage nematodes, but it’s not just about crop rotation, but the varieties chosen within those crops,” Mr Penberthy said.

“With wheat there’s a massive difference. Strzelecki can blow your rotation out, but some of the new varieties coming through like Suntop, Sunguard and Lancer look really good from the preliminary testing, as well as having good crown rot tolerance.”

Using chickpeas in a crop rotation allows populations to build up quickly as many varieties are susceptible to Pt.

“Coming out of a chickpea crop you need to make sure you know your numbers because if you go with a wheat variety that’s not resistant or tolerant you could potentially drop yields by as much as 70pc,” Mr Penberthy said.

“That’s a massive yield loss, but some varieties can handle high populations of nematodes.

“That means they won't drop yield but numbers are still high for the next crop.”

MISSING a summer crop at “Blue Hills”, Narrabri, resulted in a higher than average nematode population in one of Ian Gourley’s paddocks.

Mr Gourley tested for nematodes and crown rot for years, usually identifying average population rates across his 4047-hectare property.

With little rainfall leading up to summer planting, Mr Gourley was unable to plant cotton, which would have kept the nematode population in check.

“We were out of whack with the rotation after missing the normal summer crop,” Mr Gourley’s agronomist Drew Penberthy said.

“We would’ve gone into cotton and broken that cycle but we never got the planting opportunity, and consequently, nematode numbers were higher at testing.”

Mr Gourley (pictured with his assistant manager Aiden O’Rourke) will plant Lancer or Suntop wheat in that paddock instead of his first choice, Sunbri.

He’s looking to sow 1620ha of wheat, including durum, 405ha of faba beans, 605ha of chickpeas and 200ha of canola.

Managing nematodes through crop rotations has been trial and error, with Mr Gourley able to find a balance between summer and winter crops.

“We’ve found the nematodes are easier to manage when we have a durum and cotton rotation, because it keeps them in control, then chickpeas blow the numbers out again,” Mr Gourley said.