C-DRONE GUIDE · 11 SEPTEMBER 2026
Prune d'Agen and drones: water stress and ripeness, price
Prune d'Agen has held Protected Geographical Indication (IGP) status since 2002 across 10,500 hectares spread over six south-western departments — Lot-et-Garonne leading with 79% of 2024 volumes, ahead of Dordogne and Gironde. A long-standing sector that produces around 35,000 tonnes of dried prunes a year on average, yet has just strung together two seasons of decline: 30,500 tonnes in 2024, then a further drop in 2025 driven by hailstorms in May-June and two heatwaves, one of which struck exactly as harvest began in early August. Here is what drone thermography and ripeness mapping bring to a grower or a cooperative — and what a flight does not detect.
Published on 11 September 2026, reviewed on 11 September 2026 — regulations in force as of September 2026.
A south-western IGP under climate pressure two years running
Prune d'Agen takes its name from the prune d'Ente variety, dried exclusively within a protected geographical area since 2002: 10,500 hectares spread across Lot-et-Garonne, Dordogne, Gironde, Tarn-et-Garonne, Gers and Lot, which together account for 99% of national production. Lot-et-Garonne dominates with 79% of 2024 volumes, well ahead of Dordogne and Gironde at 7% each. In a normal year the sector produces around 35,000 tonnes of dried prunes.
The last two seasons have broken from that average. 2024 had already seen a decline to 30,500 tonnes; 2025 drives the point home with a further drop, driven by violent storms sometimes accompanied by hail in late May and early June, then two heatwaves — the second striking in early August, exactly as prune d'Ente harvest begins. Despite this erratic weather, quality has held up: fruit size in line with the ten-year average and sugar content up 6 points on the 2015-2024 average.
What a peach-orchard study documents for the plum
No drone study dedicated to the prune d'Ente plum (Prunus domestica) could be identified: it is a regional crop, outside the main circuits of agricultural remote-sensing research. The botanical genus Prunus has, however, been studied on the peach side. Bellvert, Marsal, Girona, Gonzalez-Dugo, Fereres, Ustin and Zarco-Tejada, in a study published in 2016 in Remote Sensing, compute a CWSI (Crop Water Stress Index) from airborne thermography on three Prunus persica cultivars — peach, nectarine and Saturn peach — tracked over three seasons (2012 to 2014) (see the study on Google Scholar). The authors show that this thermal index closely tracks the tree's seasonal water status, including its rapid shifts during peak water demand.
Peach is not plum: this reference is a deliberate extrapolation between two species of the same botanical genus, sharing broadly comparable water-stress physiology (deciduous foliage, stone fruit, known sensitivity to water availability during fruit sizing). It is a methodological starting point, not direct validation on the prune d'Ente.
What a drone flight brings to a grower or a cooperative
Two uses stand out for a prune d'Ente orchard. The first is water-stress monitoring during fruit sizing, between June and July, ahead of the mid-August to mid-September harvest: a repeated thermal flight, on the CWSI principle extrapolated from the peach study, flags under-irrigated zones before stress becomes visible to the eye — a useful marker after two seasons running in which hailstorms and heatwaves struck at the worst point of the cycle.
The second use is mapping ripeness heterogeneity ahead of the mechanical harvest campaign. Prune d'Ente is picked with a trunk shaker, and ripening that suddenly compresses under a heatwave — as in 2025, when harvest concentrated into three weeks with fruit ripening all at once — puts pressure on both shaker scheduling and drying-kiln capacity. A vegetation index mapping heterogeneity between orchard blocks helps prioritise the harvest order when everything ripens together, rather than moving crews from plot to plot at random.
Two things not to expect from a drone: neither sugar content nor fruit size is measured by aerial imagery — those indicators are checked in the lab or at the drying kiln, on a sample. Nor does a drone detect sharka (Plum Pox Virus), a quarantine disease under mandatory nationwide control since the order of 9 July 2021: in communes recognised as contaminated, regulations require ground-based visual prospection, with at least two passes 30 days apart between flowering and full leafing, to spot the characteristic mosaic and deformation symptoms on leaves and fruit.
Where to fly in Lot-et-Garonne and south-west France
The prune d'Agen belt largely overlaps with the hazelnut belt: the same south-western departments, terrain flat to gently rolling with no particular airspace constraint for the vast majority of plots, which fall under the open category, subcategory A3. The point worth checking before any flight is the proximity of a local aerodrome (Agen-La Garenne, Bergerac-Dordogne-Périgord, Villeneuve-sur-Lot) or a temporary restricted zone, via the Géoportail drone zone map cross-checked against the French AIP; if a plot falls under a control zone, coordination follows the process set out in our guide to missions inside an aerodrome control zone.
The same principle of water-status monitoring and ripeness mapping, adapted to other south-western orchards, applies to walnut orchards, another nut crop in the same belt facing its own water constraints, and to spring frost detection, a distinct climate risk but just as decisive for a plum orchard early in the season; our page on precision agriculture by drone covers the thermal and multispectral method across all types of vegetation cover.
Prices observed in 2026
A prune d'Ente orchard is priced mostly on a targeted campaign, ahead of the peak water-demand period and then before harvest for ripeness. Ranges observed in France in 2026, excl. VAT:
| Service | Range (excl. VAT) |
| Water-stress thermal flight (CWSI index, up to 5 hectares) | €350 to €600 |
| Ripeness-heterogeneity multispectral flight (up to 5 hectares) | €300 to €550 |
| Additional pass per extra 5-hectare block | €90 to €160 |
| Multi-year orchard monitoring (2 to 3 passes a year) | on quote |
These amounts cover the flight and delivery of a usable map within 24 to 48 hours; they do not include actually managing irrigation, sharka prospection, or fruit-size and sugar-content analysis, which remain the grower's, the cooperative's or the relevant plant-health service's responsibility. For a growers' group in Lot-et-Garonne bringing together several neighbouring orchards, a grouped campaign meaningfully cuts the cost per hectare. Request a quote stating the area, the orchard's age and the intended period: June-July for water stress, early August for pre-harvest ripeness.