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Author: François DROUET.
Photographs: François DROUET.
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Attacks variability over the season
Below, personal observations (no information reported from the literature). Toulon region; French eastern Mediterranean coast; USDA zone 9b.
3-PHASE ATTACK PATTERN
I observe a variability of the Black Fig Fly attacks over the season, responding to a general attack pattern which shows the existence of 3 phases.
Phase 1: intense attacks concentrated on a short duration. For a given fig tree, this phase concentrates 75 % to 97 % of the ovipositions of the season, and lasts from 2 to 3 weeks, depending on the variety and the tree location. Knowing that its intensity (ovipositions percentage) is not proportional to its duration.
Phase 2: very low attacks level. During this phase the number of attacks is always significantly lower than the number of unripe figs of the size required for the attack that are present on the tree. And there is a regular presence of feeding black fig flies on it.
Phase 3: total absence of attacks. Being emphasized that during this phase, immature figs with the size required for the attack of the Black Fig Fly are still on the fig tree, and there is a regular presence of feeding black fig flies on it.
Notes: the severity of the season attacks depends on the percentage of affected figs - related to the global crop - during the phase 1. Not on the percentage of the attacks of the year during this phase. The level of the attacks in an orchard is the conjunction of four factors: the orchard location in the region affected by the Black Fig Fly, the figs varieties susceptibility to the Black Fig Fly, the orchard management (density, fig trees shape, pruning), and the specific activity level of the Black Fig Fly for the considered year.
Black Fig Fly female laying eggs under an ostiolar scale of an unripe fig.
ATTACK PATTERN VARIATIONS
The general attak pattern of the Black Fig Fly may apply with some differences from one fig tree to another. The differences exist for the 3 phases, and depend on the fig variety and, for the biferous varieties, on the nature of the crop (breba crop or second crop). They relate to the duration and the intensity level for the phase 1, and to the duration for the phases 2 and 3. Below, some examples, for the year 2019, in my orchard.
For the phase 1: 'Bellone' variety 90 % of the attacks / 12 days; 'Col de Dame Noire' 97% of the attacks / 23 days; 'Grise de la Saint-Jean', breba crop 75 % of the attacks / 17 days, 'Grise de la Saint-Jean', second crop 88 % of the attacks / 20 days.
For the phase 2: duration 3 to 5 weeks for 'Bellone', 'Col de Dame Noire' and 'Grise de la Saint-Jean' (second crop), 2.5 months for 'Grise de la Saint-Jean' (breba crop).
For the phase 3: duration of 3 to 6 weeks for 'Bellone', 'Col de Dame Noire' and 'Grise de la Saint-Jean' (second crop), 8 days for 'Grise de la Saint-Jean' (breba crop).
For a given fig tree, the start date of the intense attacks phase varies from year to year (sometimes a 2 weeks variation). We must keep in mind that, the criterion that triggers this phase is not a date, but the attainment of the critical diameter for the Black Fig Fly attack (1,1 cm) by the unripe figs, on the considered fig tree. In practice, I consider that this is the case when the five largest figs
on the tree have reached this diameter (measurement with a vernier caliper; measuring the largest diameter of the fig, the syconium not being a regular sphere).
Black Fig Fly female laying eggs under an ostiolar scale of an unripe fig.
I am sure of my observations in my orchard relative to the variability of the attacks over the season. But I am not sure that they are unviversal in scope. I suggest to check in other regions if there is a variability of the attacks over the season, and if yes, if it is more or less in accordance with the exposed attack pattern. This remark particularly applies to commercial orchards, for which I have no observations in my region for a possible variability of the attacks.
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