Earth mites can devastate Canola crops. But research has led to a three-point strategy to keep the Canola growing and healthy.
The strategy stems from GRDC-funded work by Agriculture Victoria and La Trobe University. According to senior entomologist, Garry McDonald, it involves:
- rotation of non-host crops to minimise the build-up of mite infestations before planting Canola;
- border sprays to prevent mite movement into crops; and
- targeted insecticides used when mite numbers exceed an economic threshold.
Mites don't like chickpeas, lupins
"The threat of mite attack is so serious that farmers often resort to applying insecticide before the crop is sown," Dr McDonald said. "This 'insurance' approach is mostly effective in the short term but will probably lead to insecticide resistance and the death of the mites' natural enemies.
"While further field trials are necessary in 1996, there is now very firm evidence that crop rotations involving one of the crops which mites do not favour, particularly chickpeas or lupins, planted before Canola, should eliminate the mite problem in establishing Canola.
Crops such as chickpeas and lupins cause the mites largely to disappear from a paddock by the end of a season, and few should hatch the next year when susceptible crops like Canola are germinating.
"The success of this will depend, however, on the crop being kept relatively free of weeds."
Dr McDonald said it was common for large numbers of mites to invade from neighbouring crop headlands, roadside verges and fence-lines. The second prong to the strategy, developed after trials in 1995, was therefore for border sprays covering 5-10 m to exclude mites from susceptible crops.
Insecticides would still play a central role in mite management but they needed to be used more judiciously because of the recent development of insecticide resistance in mites.
To avoid entrenching resistance, chemicals should only be used when mite infestations threatened crop safety. The current threshold in Canola was an average of 10 mites per 10 X 10 cm square, although this was being further tested in 1996.
Dr McDonald said a longer-term approach to mite management in Canola was the prospect of breeding resistant varieties. There was potential for this by examining existing germplasm and through genetic engineering.
Subprogram 2.11.25 Contact: Dr Garry McDonald 03 9479 1660