10 November 2000 Nematode infection in lucerne – warning from Lincoln scientist

A warning for farmers to sow stem nematode resistant cultivars of lucerne comes from Dr Derrick Moot, Senior Lecturer in Plant Science at Lincoln University, after sampling several infected paddocks in the Hawarden and Waikari districts recently.

Dr Moot urges farmers to ensure they sow resistant cultivars because stem nematode has the potential to cause widespread crop failure for susceptible lucerne cultivars.

Dr Moot was encouraged to see many dryland farmers returning to lucerne as a source of high quality feed suitable for free draining drought-prone soils, but he fears farmers could soon lose heart with the crop if they experienced stem nematode attack.

"Plant breeding in New Zealand and overseas has produced several stem nematode resistant cultivars," he says, "and farmers should use these if they want to maintain stand persistence and increase resistance to pests and diseases.''

The number one pest in lucerne in New Zealand is stem nematode – this is a small worm-like parasite that lives in the stem of lucerne plants and causes stunted growth. Farmers may initially see patches in their crop that are short. The rest of the crop begins to increase in height while these patches remain short and are often colonised by weeds such as dandelion. The nematode lives in the lucerne stem so cutting or grazing will remove the nematodes but not kill them. They fall to the ground on plant trash and are then able to reinfect the newly developing stems of the following regrowth crop.

A major source of infection is the movement of infected plant material on stock or machinery from an infected to non-infected area.

"Farmers with infected crops should harvest or graze these paddocks last in their lucerne rotation and then put stock on to grass based paddocks," he says.

"Making hay from an infected crop does not reduce the problem. Nematodes can live in the hay for many years – if it is then fed out onto another lucerne paddock further infection will occur."

Stem nematode is not a new problem but the moist spring in many parts of the South Island has provided favourable conditions for infection.

There is no chemical treatment available to farmers after infection, says Dr Moot, and he stresses that the only long-term solution is for resistant cultivars to be used.

Ian Collins, Journalist, Lincoln University, Canterbury, New Zealand