WHILE THERE is a real need to plant more lucerne in many regions of Australia, graingrowers also need to be able to remove it efficiently and cost-effectively before sowing an annual crop.
In collaboration with NSW Agriculture and the WA Department of Agriculture, Stephen Davies of CSIRO Plant Industry has been researching this key issue and says that the reliability of killing lucerne with herbicides increases when the legume is sprayed in early to mid-spring.
He said that this vigorous perennial could be difficult to remove prior to a cropping phase, but herbicides were more effective when they were applied during a rapid growth period of the plant.
"Removal in the spring has some advantages over removal in autumn;' Dr Davies said.
"It makes more nitrogen available to the following crop, it reduces the risk of poor yield of the following crop because the soil is too dry, and lucerne seems easier to remove. Conversely autumn removal leaves valuable summer feed for grazing and helps protect the soil against erosion. However, the first crop may require fertiliser nitrogen to optimise yield."
Some things to keep in mind
Dr Davies says farmers will have to assess all these factors in deciding whether to opt for lucerne removal in spring, or later, but regardless of the period of the year when lucerne is killed, he offers the following advice:
- The kill appears to be maximised after at least 20 mm of rainfall in the two weeks before spraying.
- The movement of herbicide in a plant, and the herbicide's efficacy, is reduced if the lucerne is grazed, mown or cultivated in the two weeks following application.
- The age of the lucerne does not appear to influence the ease of removal in lucerne stands older than two years.
- Attempts to remove lucerne by grazing alone may require high set stocking rates for prolonged periods (more than six months).
- Herbicide efficacy can be enhanced by some adjuvants but indications are that this may occur only for particular herbicide/adjuvant combinations.
Program 4 Contact: Dr Stephen Davies 0262465531