Cultural Control
Tuesday, 29 January 2013 13:27

 

Cultural control includes practices that may be regarded as part of the normal production system and do not involve the application of insecticides.  When combined with protein bait sprays in an IPM program, it results in very effective fruit fly management.


Production during periods of relatively low fruit fly activity

Fruit fly activity and populations vary throughout the year.  Trapping data in Tonga, Fiji Islands, and Cook Islands show that populations of fruit flies are low during May, June, July and August, i.e., during the cooler months.  Damage caused by Bactrocera facialis to capsicums in Tonga at this time of the year, for example, is relatively low - less than 10%.  Therefore, the growing of capsicums in Tonga in May-August may be worthwhile, considering that New Zealand authorities may be prepared to accept seasonal abundance data and data on seasonal damage levels in low risk crops as part of a move to recognize a ‘winter window’ for importation of some commodities.  The combination of low fruit fly activity and effective field control in the exporting country during cooler months and the low risk of establishment of fruit flies in winter months in the importing country may open up new markets for low risk fruit fly host commodities.  Also, growing crops during the cooler months reduces pressure on the effectiveness of field control systems, such as protein bait sprays.


Growing less susceptible varieties

With the advent of a standard for testing the susceptibility of various fruits and vegetables to fruit flies, there is an option now for growing varieties that may be less susceptible or not susceptible to fruit flies.  Under the Regional Fruit Fly Project in the South Pacific (RFFP) in Fiji Islands, two varieties of chillies, 'Hot Rod' and 'Red Fire', have been cleared by New Zealand Ministry of Agriculture & Forestry - Biosecurity Authority [previously  New Zealand Ministry of Agriculture (Regulatory Authority)] for export without additional post-harvest quarantine treatment.  These varieties are classed as non-hosts for fruit flies in Fiji Islands.

 

Similarly, fruit crops such as lychee and rambutan are not infested by fruit flies in northern Thailand, providing the skin is intact.  Pineapples are not hosts for fruit flies at any stage of maturity in Fiji Islands.  Other crops that may be non-hosts or at least low risk in some PICTs are squash (pumpkin), zucchini, cucumber, some varieties of watermelon, rockmelon, limes, bananas. and pawpaw at colour break.  PICTs that have conducted research into non-host status include Cook Islands, Tonga, Samoa, Vanuatu, Solomon Islands, Federated States of Micronesia, Fiji Islands, and New Caledonia


Sound crop sanitation

The collection and destruction of fallen, damaged, over-ripe and excess ripe fruits is strongly recommended to reduce resident populations of fruit flies.  Evidence from Hawaii shows that pawpaws left on the ground act as a major breeding site for oriental fruit fly (B. dorsalis) and melon fly (B. cucurbitae).  To eliminate or reduce this resident population reservoir, crop sanitation should be an essential component of melon fly and oriental fruit fly programs in pawpaw orchards in Hawaii.  Initial results from sampling kumquats (Fortunella japonica) in Fiji Islands indicate similar trends to those of pawpaw in Hawaii.  Thirty-five percent of the fruits on the ground were infested with B. passiflorae, while about 7% of fruits on the tree at a similar stage of maturity were infested.  In some areas of China, B. minax, a highly destructive pest of citrus, is successfully controlled by large-scale, area-wide destruction of fallen fruits in orchards and villages.




Fallen carambola fruits under trees constitute breeding grounds for fruit flies. (Photo: A. Allwood)

Crop residues such as fallen, over-ripe or damaged fruits may be destroyed by deep-burying (> 50cm) or by burning, or they may be fed to pigs.  Alternatively, they may be sealed inside plastic bags and exposed to direct sunlight for several hours.  Putting fruit or vegetable residues into compost heaps or rubbish dumps is not recommended.  Not adopting sound crop sanitation places unnecessary pressure on other components of control systems, particularly protein bait sprays, whose effectiveness may be threatened under high fruit fly population pressure.  Under quality assurance schemes being adopted for production of export commodities, sound crop sanitation is an essential component and a prerequisite for any farm that is registered for export production.


Early harvesting

Avoidance of fruit fly infestation is possible by harvesting crops at a stage of maturity when fruits or vegetables are not susceptible to fruit fly attack.  Bananas, for example, have been exported around the world because they are not susceptible to fruit flies at the mature green stage, except in countries where banana fruit fly (Bactrocera musae) and Asian papaya fruit fly (B. papayae) occur.  On that basis, Samoa exports large amounts of green bananas to New Zealand. Banana fruit flies may lay eggs in very young banana fruits.  Eggs do not hatch until the fruit commences to ripen. Asian papaya fruit fly may also infest green bananas.  Pawpaws, harvested at color break, are less likely to be infested by fruit flies than if harvested at later stages of maturity.  Harvesting at color break has become one of the conditions for export of pawpaws from Cook Islands and Fiji Islands to New Zealand.