The olive fly, a small insect, becomes a major concern for olive growers from June to November. On extensive crops, Bactrocera oleae can cause significant damage, potentially ruining an entire harvest and posing problems for both the olive trees and farms. The best way to combat it without resorting to insecticides is to ensure there are few specimens circulating during its reproduction period.
Not every year is the same: the fly’s arrival and the extent of the infestation depend largely on the climate, as well as on adopting good habits throughout the year to maintain an ecosystem that is as unfavorable as possible for its reproduction. Let’s explore how.
- 1 WHAT IS OLIVE FLY
- 2 OLIVE FLY INFESTATION AND DAMAGE
- 3 DEFENSE STRATEGY
- 4 FLY TRAPS: ESSENTIAL IN DEFENSE
- 5 VIDEO SPIEGAZIONI
- 6 USEFUL TIPS
WHAT IS OLIVE FLY
Bactrocera oleae is a fruit fly widely distributed throughout the Mediterranean. In Italy, it is firmly established not only in coastal areas (more humid) but also inland, infesting olive groves from June to the last autumn harvest. It reproduces rapidly in climates with favorable conditions, characterized by humidity and temperatures ranging from 20 to 30 degrees Celsius. Each year, it goes through five to six generations. Similar to other fruit flies, the olive fly is a carpophagous species that feeds on the flesh of the fruit. It attacks olives as small as chickpeas, biting them and depositing eggs. Upon hatching, the larvae begin to consume the olives, rendering them inedible, unmarketable, and causing premature dropping.
OLIVE FLY INFESTATION AND DAMAGE
The mere act of the olive fly biting the olive initiates the first form of damage: the bitten olives become susceptible to pathogens that cause plant diseases. Furthermore, its infestations bring more than a few challenges for growers. The bite negatively impacts the taste of the olives and degrades the quality of the extracted oil, making it more acidic and prone to mold. In the most severe infestations, distinguishing between good and bad olives during harvest becomes very difficult. Infested olives are inedible, leading the grower to potentially forgo harvesting the entire plant. Needless to say, this poses a significant economic threat to producer companies.
AT WHAT TIME IT ATTAKS OLIVES
The fly typically appears around June, but in recent years, a significant presence has also been observed in spring. This is attributed to climate changes resulting in milder winters. It’s not uncommon for the last generation of the previous year’s fly, which has overwintered in the soil or fallen olives, to disperse early.
HOW INFESTATION OCCURS
When the eggs hatch, the larvae start consuming the flesh of the olive, creating tunnels and causing decay. To become adult flies, the larvae undergo their pupal phase (growth phase) inside the olive itself. In warmer months, the adult fly emerges directly from the olive, while in colder months, the larvae fall to the ground and pupate in the soil or in fallen olives. This aspect is crucial as it emphasizes that olive fly control necessitates preventive measures throughout the year, such as reducing fly populations in spring and eliminating overwintering pupae in winter.
Effective defense always requires early action, such as preventive trapping or specific types of treatments, along with a set of good practices. The goal is to minimize the number of adult flies circulating during the favorable reproduction period.
GOOD PRACTICES ALL YEAR ROUND
- Maintaining soil health is a top priority for sustaining the vitality of olive trees. In this regard, hosting various types of plants and mowing the lawn only at specific times is beneficial. Wild grasses contribute fertility to the soil and foster biodiversity.
- Leaving plant or grass clippings on the ground provides nutrients and organic substances for the community of living organisms in the soil.
- Proper pruning of plants is essential for the health of olive trees, promoting air circulation and preventing moisture that attracts flies. Additionally, correct pruning enables the harvest of all fruit, preventing olives from lingering on the tree and becoming a breeding ground for next year’s flies.
- Allow domestic animals and small fauna to graze, including hens, goats, sheep, hedgehogs, hares, and mice. Their presence fertilizes the soil through droppings and helps control larvae on the ground, including those in the olives.
- Implement treatments to protect plants and deter fly bites using natural materials such as rock, kaolin, zeolite, or bentonite powders. These substances, reduced to flour, create a ‘mask’ on the olives with a white patina, deceiving the fly and making bites more challenging.
- Harvesting olives early, typically before reaching maximum colour and size, reduces the risk of fly damage as the crop is harvested at a stage unsuitable for reproduction. Moreover, early-harvested olives yield oil with greater stability, higher polyphenol content, and a more robust flavour.
FLY TRAPS: ESSENTIAL IN DEFENSE
The core of the defense strategy against the olive fly lies in the effective trapping that inevitably disrupts its reproduction by reducing the number of adults in circulation. This practice is beneficial as early as June but becomes essential at the end of the season to capture even the last specimens in circulation. To do a thorough job, two types of traps are necessary.
- Tap Trap: Deployed in the field throughout the year for an effective and continuously active defense against any climatic variation.
- Pheromone traps for monitoring: Employed during periods when we anticipate the fly’s arrival to detect its presence and assess the extent of infestation.
TAP TRAP ALL YEAR ROUND
The Tap Trap for the olive fly activates quite swiftly. The bait prepared is selective for flies, allowing the trap to activate with the help of captured specimens. As these flies macerate inside the trap, they release substances like putrescine, which, in turn, attract other flies. Since this bait attracts various fly types, it doesn’t need replacement during the season and can stay in the field all year round. When the olive fly season begins, it’s beneficial to add unscented ammonia (typically used for cleaning) to the trap once a month or whenever the bait appears slightly dried out. Fruit flies particularly appreciate ammonia substances. Detailed instructions on preparing the bait and placing the Tap Trap in the olive grove can be found in this article on the Olive Fly Trap with Ammonia.
GLUE TRAPS WITH PHEROMONES
In June, we can combine Tap Trap with glue traps containing pheromone attractants. Pheromones are chemical compounds utilized in traps to mimic the substances emitted by insects during the mating season for communication. They serve as a potent attractant and include a glue panel to help us tally the number of flies caught. This count aids in gauging the severity of the impending attack. However, it’s essential to be cautious as these traps are not selective, and other types of insects may get caught on the sticky panel. It’s advisable to refrain from using them when plants are in bloom.
It’s great to hear that our friends from Bosco di Ogigia have produced an engaging video in Cristiano Gallinella’s olive grove, showcasing how to implement the strategies mentioned here to deter the reproduction of the olive fly. Watching the video provides a practical demonstration of these techniques. Click on the photo to check it out!
Where to find Tap Trap for olive fly
- To find out which dealer is closest to you, please send an email a email@example.com, or fill out this form
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Foto cover: – Depositphotos
All photos, unless otherwise indicated, are Copyright Roberto Carello et Vanda Bellini.