Fruit production: Manage fruit flies


By Digital team | 12 September 2018
fly; flies
Photo: Scott Bauer on Commons.wikimedia.org

Fruit flies are among the most damaging pests to fruit. Using baits should be an integral part of managing them holistically.

Fruit fly baits are often not used, or not used with sufficient attention or urgency. For this reason, the fruit industry has compiled baiting guidelines for farmers and contractors.

These baits contain a protein base as attractant and food source, in combination with a toxicant. Fruit flies aren’t attracted by the protein, but by small quantities of ammonia released by the degradation of protein hydrolysate, normally used in fruit fly baits.

For the best results and to ensure attraction, the correct dosage of protein-based product (800 ml to 1 litre/ha) should be applied.

APPLICATION

  • Growers should try to apply the bait in scattered droplets of 1 mm to 3 mm in diameter to the inside of tree canopies (for deciduous fruit and citrus).
  • For table grapes, bait mixtures shouldn’t be applied directly to bunches of fruit, but rather to the underside of the trellis roof above the bunch line (for slanting trellises) or between bunch lines (for overhead trellises).
  • Avoid using application equipment that results in a covering effect (small droplets).
  • Studies have shown that the best results are obtained when the bait is applied with a relatively thin jet, at relatively high pressure, directed at an angle into tree canopies.
  • When the jet makes contact with any obstruction such as leaves, twigs or fruit, it breaks up into scattered droplets inside the tree canopies.

This method has the following advantages:

  • The bait droplets are protected against direct sunlight.
  • Less fruit is in direct contact with the bait.
  • It minimises the risk of possible residues on the fruit.
  • Bait should be applied to every tree row.
  • If applied from both sides of the equipment, this could be every second work row.
  • The swathe width for bait application shouldn’t exceed 12 m.
  • In practice, row widths vary from 3.5 m to 6 m.
  • To change calibrations for every row width is impractical, so equipment could be calibrated according to the average row width for a particular farm or crop type.

Take the following into consideration when it comes to nozzle settings:

  • The pump capacity must be able to maintain a nozzle pressure of 1.5 BAR to 2.0 BAR.
  • The hollow cone nozzles of the spraying system.
  • D-1 to D-3 orifice discs without whirl plates.

Use orifice discs sizes as follows:

  • D-1 to D-2 minimum pressure at 1.5 BAR.
  • D-3 minimum pressure at 2.0 BAR.
  • Using orifice sizes larger than D-3 are not recommended.
  • For higher volume applications, 2 to 3 nozzles per side of application equipment may be used provided that the minimum nozzle pressure recommended for the specific orifice sizes can be maintained.
  • The smaller the orifice size, the better the results.
  • Use lower ground speed to compensate for higher volume requirements.
  • Always remember that the thicker the jet, the higher the nozzle pressure should be.
  • Although bait can be applied every 10 to 14 days during early summer (before end of November), the intervals should be shortened to 7 to 10 days in summer until all crops have been harvested and orchards or vineyards have been picked clean.

If all recommendations for fruit fly management are adhered to, there should be no reason why intervals should be shorter than 7 days, even if fruit fly numbers increase towards the end of the season.

DO’S AND DON’TS

  • Where and whenever possible, bait should be applied early in the morning.
  • Don’t apply bait to wet trees.
  • Apply the recommended volume of bait (and protein-based product) per ha.
  • Use pheromone traps to monitor fruit fly activity.
  • These shouldn’t be moved during the growing season.
  • Keep weekly records of fruit fly numbers per trap and replace pheromone capsules in time.
  • During winter, traps can be moved to the farmyard, home gardens, or green crops or trees in the surrounding area.
  • Where possible, apply baits consecutively in alternate work rows.
  • Orchards or vineyards should be picked clean and fallen fruit should be collected and buried.
  • Monitoring and bait applications should be maintained in post-harvest orchards and vineyards until at least one month after the last cultivar or crop on the farm (or neighbouring farm) has been harvested.
  • Treat home and farmyard, or any other host plants or hot spots once a month during winter.

FRUIT FLY PHYSIOLOGY

  • The highest numbers of fruit flies occur during summer.
  • Numbers usually peak from December to the end of April, if orchards of early fruit aren’t picked clean and where a lot of over-ripe fruit makes an ideal breeding source from where the fruit flies enter new orchards of ripening fruit.
  • The basic needs of young fruit flies are food, water and mating.
  • For mated females, they are food, water and suitable fruit of a host plant to lay their eggs.
  • Although fruit flies are very mobile, there’s no need for them to move out of an area where there is a supply of basic needs.
  • When a nearby source of host fruit is ripening, females will move to that new source and males will follow.
  • Young fruit flies, within the first four to five days after emergence from the pupal case, are the best target group for baiting.
  • At this stage, a food source is a high priority to both males and females.

Also read: Bats are nature’s pest control agents

  • This article was written by Rittie Smit and first appeared in Farming SA.