ORGANIC MED FLY CONTROL- “CERATITIS CAPITATA”

The Mediterranean fruit fly known as well as the Med Fly – “Ceratitis Capitata” is of great importance to the Maltese fruit grower. This pest causes great losses to the fruit industry in the whole Mediterranean region. There are various species. Few of them are more aggressive than others and offer harder resistance to synthetic chemicals.

Hence organic fruit fly control is much more effective and reliable than any other forms of conventional uses.

Life cycle of Med Fly

Med Fly takes only 4 weeks in Malta to develop from egg to adult. In Queensland, Australia a different species takes 5 weeks to develop. The females (fly) lay their eggs in small groups just beneath the skin of fruit. The maggots hatch and by their feeding, they create tunnels, which are exposed to bacteria . Following the mechanical injury done by the maggot feeding and biological damage caused by the multiplication of bacteria  to the flesh of the fruit , the  pedicle  whose function is to keep and support the fruit attached  to the tree  shrinks and dessicate prematurely. This results in fruit rot and as the pedicle gets weaker to support the weight of the hanging fruit, the fruit falls on the ground. When the maggots get full size inside the rotten fruit, they leave the fruit and burrow into the soil. Once , they find their own niche in the soil , they quiecent and transform into a furthern stage – the pupa.

The pupal stage develops according to climatic conditions. However, adults can live for many weeks and flies commonly over winter as adults. They become active when the weather warms up around June and gradually the population reaches peak in late summer.

Sometimes , tiny flies are seen hovering around the fruit bowl and these are just fungal gnats , which are attracted by decomposition .

Different methods of control

Various methods can be applied to control flies. Physical and biological controls involve more labour and biological agents costings   and this amount to about 15 % higher costings than chemical applications.

• Removal and destruction of rot fruit

Fruits that are infected need to be removed from the tree with weeping clear sap. This is much more effective than just picking up rotten fruit from the ground as the maggots may have already burrow into the soil and are about to pupate. Removal and destruction of rotten fruit before the maggots pupate is a fundamental physical control and the rotten stuff can be fed to poultry.

• Selection of resistant fruit trees cultivars

Ideal situation is to avoid planting fruit fly prone varieties of trees to eliminate all possible attacks. But , if dwarf trees or espalier trees are grown for easier management   where manual handling of the trees is accessible from ground level , then less machinery and less equipment to manage high tops of trees induces less costs in the fruit industry.  This is a good practice and in principle , fruits which cannot be easily handled  manually should have their high branches cut off .

• Exclusion of flies

Exclusion of flies on the fruits can be easily done if the trees are within an arm’s reach of the gardener. Fruit clusters or even a whole tree can be covered by netting. It sounds time consuming but can be very profitable and rewarding as compared to the use of chemical sprays through the fruiting season. Commercial fruit fly exclusion bags are available in either waxed paper or cloth. Bags even made from newspapers can be an alternative source to cover fruits as soon as they are formed.

• Waxed paper fruit bags

Waxed paper fruit bags exist in different sizes, which are suitable for stone fruits. Early in the season thin the fruit, then simply twist a bag over each remaining cluster of fruit, using the built-in twist tie. Such bags are also effective against the codling moths and against birds.

• Biological control

This can be very effective against fruit fly. There are various parasites and predators.

Ants and ground beetles feed on the maggots.  Braconised wasps are egg parasites. Spiders, dragon flies and birds such as swallows eat the adult flies.

Chicks reared in free range fetch for pupa and maggots in the soil. Free layers turn rotten fruit into eggs and happily spend hours scratching beneath trees in search for fruit fly pupae. As it takes adult fruit flies about 24 hours to harden their wings after emerging from the pupae, the day is a critical point for their survival as chicks prey on them.

• Least Toxic Control

Pheromone traps are currently available to attract male fruit flies only, so they are useful only as an adjunct to some other form of control.

• Non Organic Fruit Fly Lure

Female flies are attracted to baits based on food attractants as female flies need protein in order to begin egg laying. The yeast autolysate bait is mixed with an insecticide and sprayed onto the lower leaves of trees. A splash bait every two weeks during the fruiting season can be used as non-organic to kill both male and female fruit flies of all species.

Horticultural advice

Advice

RHS Help & Advice

Glasshouse red spider mite (Tetranychus urticae)

Plants affected

A wide range of glasshouse plants, houseplants and  garden plants.

Symptoms

A fine pale mottling develops on the upper leaf surface. In heavy infestations fine silk webbing can be seen on the plants, the leaves lose most of their green colour and dry up or fall off. Heavily infested plants are severely weakened and may die.

A very wide range of plants in glasshouses and homes can be attacked, and red spider will also cause problems in gardens in late summer, especially in hot dry summers. Large numbers of mites, up to 1mm long, and spherical eggs can be seen on the lower leaf surface (easier to see with a x10 hand lens).

Cause

Despite their name, during the spring and summer these sap-sucking mites are yellowish green with a pair of darker markings. They only become orange red during the autumn-winter resting period. Because of this they are sometimes called the glasshouse two-spotted mite.

Control

Glasshouse red spider mite can be difficult to control as it breeds rapidly in warm conditions and some strains of the mite have developed resistance to some insecticides. Biological control is an attractive alternative to using insecticides as it avoids resistance problems and the risk of spray damage to the plants.

Biological control

A predatory mite (Phytoseiulus persimilis) feeds on the eggs and active stages of glasshouse red spider mite. It needs good light and daytime temperatures of 21^oC (70^oF) or more on a regular basis if it is to breed faster than the pest. Its effective period of use is normally April to October.

As the predator is susceptible to insecticides, biological control cannot be used in conjunction with most chemical controls. The exceptions are those with very short persistence, such as plant oils or extracts (Vitax Organic 2 in 1 Pest and Disease Control, Growing Success Fruit & Veg Bug Killer) or fatty acids (Bayer Organic Pest Control, Doff Greenfly and Blackfly Killer, Fito Get Off Insect or Greenfingers Organic Pest Spray), which can be used to keep mite numbers down before it is time to introduce the predator.

Phytoseiulus and compatible biological controls for most other greenhouse pests can be obtained by mail order from specialist suppliers.

Chemical control

Insecticides containing bifenthrin (Bayer Sprayday Greenfly Killer Plus, Scotts Bug Clear or Doff All-In-One Garden Pest Killer) will control red spider mite, provided it has not gained resistance to this substance. Alternatives are sprays containing plant oils, plant extracts or fatty acids (see above). The latter pesticides may require more frequent applications.

Andrew Halstead

Source: Royal Horticulture Society http://www.rhs.org.uk/advice/profiles0601/red_spider_mite.asp