Pastures
During spring and summer, insecticides can be used by landholders to control locust infestations that could damage pasture.
Hopper and adult locusts can cause considerable damage to pastures. It is estimated that 20 hoppers per square metre eat the equivalent of three to five sheep per hectare each day. Damage to pastures by locusts will affect both the quantity and quality of pasture. Locusts will consume green pastures and pastures that have begun drying off.
Hoppers develop over six to eight weeks, depending on temperature. If green or drying pasture is available over this period, hoppers may complete their development at one locality and consume most of the pasture. Adult locusts may fly into a paddock and although their stay may be short, they can still consume a considerable amount of pasture. It may not be possible to effectively protect pasture in these situations.
Perennial pastures such as lucerne, long-season annual pastures and newly-sown pastures are at greater risk from locust damage later in the season, as they tend to remain greener for longer periods.
Locust attack has the potential to destroy one to two year old tagasaste and to strip older trees.
Growers need to identify high value pasture paddocks for special emphasis on control measures. These include newly sown pastures, pastures set aside for specialist seed production and lucerne. Any degradation to pastures caused by locusts may subsequently result in erosion in prone paddocks. Consideration needs to be given to the increased erosion risk on sandy soils if vegetative cover is removed. This may subsequently limit opportunities for grazing.
Treatment of locust swarms will need to be within hours of them arriving, which means frequent monitoring from mid-October onwards, if large infestations are in your area.
Withholding periods for livestock grazing and slaughter should be observed at all times.
Management options
- Hopper control in pastures is economic if hopper densities exceed 20 per square metre, if pasture is valued at the cost of replacement feed for livestock.
- Adult locust control in pastures is economic if locust densities exceed 10 per square metre.
- Other factors to consider in the decision to spray locust hoppers in pasture include:
- Pasture availability – whether there is a surplus or deficit of pasture on the farm.
- Stage of pasture growth – green pastures and pastures that are drying off are very susceptible to hopper attack, but pastures that have completely dried off are not favoured.
- When the pasture has completely dried off, other green plant material in the paddock or nearby may be damaged, for example, tree seedlings.
- If you consider it necessary to spray for locusts refer to DPIRD's registered insecticides web page for chemical options and DPIRD's spraying guide for withholding periods.
- Abide by the withholding period in sprayed paddocks.
- Where possible, the over-spraying of stock should be avoided. Otherwise, withholding periods apply.
- Consider spray-topping or hay-freezing additional low-value pasture paddocks. You will need to consider the relative costs of these pasture management treatments versus spraying locusts – which is the cheapest?
- Consider grazing or spraying established lucerne or other perennial pastures prior to locust attack.
Strategies to consider include:
- Reducing carrying capacity by selling livestock and/or agistment.
- Fodder conservation by making silage, hay and sacrificing crops.
- Supplementary feeding in conjunction with estimates of feed reserves, feed budgeting, retaining grain and lot feeding.