Transverse ladybird attacking bluegreen aphids
Lucerne is not only attacked by insect pests, but also provides food and shelter for the predators and parasites of these and other pests. Since lucerne is a perennial crop, beneficial insects are able to live on each year and also spread to neighbouring annual crops, which are not available to support them continuously. The lucerne crop is, therefore, important as a reservoir and nursery for beneficial insects and should be managed accordingly.
Lucerne can sustain some insect damage with very little loss of yield. Growers can obtain maximum benefit from natural controlling agents by allowing some pest species to remain in their fields. Spraying often upsets the balance between pest and beneficial insect populations, stimulating the resurgence of the pest and making repeated treatments necessary. Pests could also become resistant to insecticides.
Insecticides are best used only when natural control is inadequate and economic losses are likely. The aim of the pest management procedures covered in this chapter is to emphasise correct timing of selected treatments as determined by the pest numbers. While there are a number of NRA-registered insecticides, which effectively control many insect pests of lucerne, the chemicals highlighted in italics (Table 4.1) have been selected because they are the least harmful to beneficial insects.
Whitefringed weevil — larva destroying roots
Insecticidal control
Effective pest management requires regular checking for insects and their damage. The NRA-registered insecticides in Table 4.1 are recommended for use when the population of the particular pest reaches the treatment level suggested above. Insecticides that are believed to have the least harmful effects on beneficial insect populations, but provide worthwhile control of the target species, are listed in italics. Insecticides must all be applied carefully with a well-calibrated boom sprayer, or from an aircraft, for the safest, most effective and economical insect control. This list does not include all pests of lucerne — only the major ones for which insecticide treatments are available.
Table 4.1 Insecticide treatments registered in Queensland for major insect pests of lucerne. Those in italics are most likely to be least harmful to beneficial insect populations.
Table 4.1
*Withholding period = number of days from pesticide application to cutting or direct grazing.
Note: User should verify withholding periods specified for each brand by checking label.
The insecticides listed are all registered in Queensland as at 2001. Some insecticides, which are registered in Queensland, but are not available, and others which are now considered to be superseded, are not included.
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