Under the Act, landholders are responsible for controlling declared pests on their land and penalties of up to $20,000 could apply if no controls are implemented by landowners.
The stable fly problem has been escalating since the mid 1990s, with the pest proving to be highly adaptable in almost any accumulation of decaying vegetable matter. The optimum larvae breeding environments have very high temperatures (55–60°C black sands, silage pits), a high degree of bacterial activity, ageing animal manures or combination of manure and vegetable matter. Therefore, managing larval habitats is the key to stable fly control.
The main stable fly breeding sources include vegetable crop residues left after harvesting, namely stalks, leaves and fruit left on the ground and harvested crop waste such as damaged and rejected produce.
Samples collected from commercial vegetable growers have shown that over 1,000 stable flies/m2can emerge from the soil of a trashed vegetable crop. Typically, one to several hundred stable flies develop from the rotting residue of broccoli, cabbage, cauliflower, celery, and lettuce crops. The sheer amount of vegetable matter on the ground represents a significant potential risk for stable fly breeding if it is left to rot for more than 3–4 days and/or is simply rotary hoed into the soil with minimal physical breakdown.
Breaking down vegetable crop residue into small pieces, will significantly reduce and even prevent stable fly breeding and have the added benefit of allowing growers to put another crop in that area sooner, which will reduce the risk of disease transmission to the next crop.
Reject produce must be either physically removed, put into an open pit, and buried weekly with at least 30cm of soil; or sprayed weekly with a high-volume pesticide application.
The vegetable crops that support stable fly development when residues of the crops are left to rot after harvest include: beetroot, broccoli, cabbage, cauliflower, celery, Chinese radish, coriander, corn, leek, lettuce, silver beet, spring onions and squashes.
Many vegetable and fruit crops that are regularly harvested over an extended period of time (weeks to months) result in rejected and/or damaged produce being left on the ground either under the crop vines or in the space between crop rows. This is often the case with crops such as eggplants (aubergines), rockmelons, watermelons, snow peas, sugar snap peas, paprikas (bell peppers), capsicums, carrots, and zucchinis.
Produce either rejected within the vegetable/fruit crop or at first stage processing and/or sorting are all capable of supporting the development of biting flies and other nuisance flies if not handled properly.
2019 Management Plan — Control measures
Stable fly larvae go through 3 larval instars; the smallest 1st instar larvae are just over 1mm when they first hatch from eggs. The 2nd instar stage occurs 2.5–4.5mm in length and the 3rd instar larvae range from 5mm up to 12–14mm long.
In determining the level of stable fly breeding on a property, it is important to gather the following information:
1 The size of the property
2 The proportion of the property where stable fly larvae/pupae are found
3 The density of stable fly larvae/pupae in that resource (number per sample or per square meter)
4 Is it an on-going problem or a one-off situation (machinery breakdown, manager away, weather conditions, accidental spillage, abandoned crop due to disease or market price fall, etc).