fig1.Adult male and female sciarid flies (Lycoriella ingenua) are attracted to compost immediately following pasteurisation

Stephen Jess* & Mairead Kilpatrick†

Applied Plant Science Division
*Agriculture and Food Science Centre
Newforge Lane Belfast BT9 5PX

†Northern Ireland Horticulture and Plant Breeding Station
Loughgall BT61 8JA

The Northern Ireland mushroom industry, comprising approximately 300 growers, annually produces more than 20,000 tonnes of mushrooms, with a market value in excess of £27M. Annual expenditure on insecticide application by the industry is estimated to be £0.9M. Presently, insect pest control is limited to the routine application of insecticides at different cultivation stages, supplemented with fumigant treatments directed at adults.  

Current constraints associated with the use of chemical insecticides and increasing consumer demand for reduced pesticide inputs necessitate the development of novel insect pest control programmes in mushroom production. A new approach to insect pest control in mushroom production is currently being investigated by the division, which, while not eliminating insecticide application, will maximise its effects in combination with cultural practices. The protected, controlled environment associated with mushroom cultivation provides suitable conditions for rapid increases in pest populations. However, the controlled environment also provides the potential to integrate pest control measures with other cultural practices to provide more effective and sustainable insect pest control.

It is possible for growers to achieve optimal insect pest control with rational insecticide use, provided they integrate cultural practices, environmental factors and biological controls. A full understanding of the biology of the pests and the nature of the damage caused is essential for effective integrated pest management.

Presently, sciarids (Lycoriella spp.) are considered the most significant insect pest during mushroom cultivation and adults may be found on mushroom farms throughout the year but more commonly between May - November. Adult flies are small, grey delicate insects with a tendency to run across surfaces rather than fly (Figure 1).  Within insulated polythene tunnels they may be observed congregating or “roosting” around the structural “hoops”. Efficient pasteurisation destroys immature stages in phase II compost but females may subsequently be attracted to the compost during cooling. Egg laying, can occur before and, up to a week, after spawning.

A second generation of flies emerges from the compost within two to three weeks, which coincides with casing operations. The casing layer provides the medium for the development of subsequent generations that damage the emerging crop.

Mushroom compost is also susceptible to attack by the phorid fly (Megaselia halterata). Adult phorids are brown-black, robust, hump-backed flies with characteristic jerky movements and they are commonly referred to as "scuttle flies" (Figure 2)**. Phorid flies are active during May to November with a peak in September. Females lay eggs in compost, which has been spawn-running for approximately 7-12 days. Egg laying, continues in the casing layer throughout the remainder of the cropping cycle. The recent withdrawal of the organophosphorus compound diazinon has compounded the difficulties associated with control of this pest and may increase its economic significance.

From the life cycles of the pests outlined above it may be assumed that the potential for infestation is primarily at the site of crop production. However, composters have a responsibility to minimise the period between compost manufacture and delivery, to reduce the possibility of infestation with by invertebrate pests.

Preventative Control Measures

• Growing tunnels should always be properly sealed to prevent adult migration into the house.
  
  
• Cracks and joints should be sealed with proprietary sealants.
  
  
• Mesh screens or filters should be inserted over fan intakes and vents.
  
  
• Personnel and loading doors should also be sealed and entry to production houses, particularly before cropping, should be restricted.
  
  
• Casing procedures should take place within the production house and personnel and loading doors should remain closed.
  
  
• Post-cropping disinfection of production houses will minimise carry-over of pests from one crop to another. Before spent compost is removed, a fumigant treatment with formaldehyde may be applied. However, owing to health and safety considerations, the Department is currently investigating the use of steam sterilisation as a crop disinfection process.
  
  
• Thorough hygiene procedures will eliminate insect breeding and roosting sites. Organic litter should be regularly removed from the production site. Stagnant water pools should not be created following hosing down.
  
  
• Fumigation of production houses will be most effective following procedures, which increase crop exposure to flies (i.e. beginning of spawn and case-runs).