Olive Fly, Copper Limits and a Neighbour's Dimethoate Spray
An organic olive grove of 3.2 ha (about 180 trees, cv. Koroneiki) near Pissouri is in its fourth organic year. In the first week of September, pheromone traps for Bactrocera oleae catch 9 flies per trap per day; 12% of sampled fruits show oviposition scars, and night temperatures are still above 20 C with 70% relative humidity. The trees also show olive leaf spot lesions after two heavy dew periods, and the grower has already applied 3.2 kg of copper per hectare this season. A neighbouring conventional grove 60 m downhill is sprayed with dimethoate. The grower wants to spray dimethoate too, at the lowest rate, and asks whether this is allowed, what alternatives exist, and when to harvest for oil.
1. Rule on whether dimethoate can be used, and justify the decision with reference to organic rules and the pest threshold.
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Dimethoate cannot be used. Organic plant protection products must be authorised under Reg. (EC) 1107/2009 and listed in Reg. (EU) 2021/1165; dimethoate is not listed, and its use would be a major non-compliance. It would put the whole harvest at risk of decertification and could leave residues above the MRL, which is exactly what the control body tests for. The neighbour's spray 60 m downhill is a drift risk to be documented and buffered, not a justification to copy.
At 9 flies per trap per day in early September the action threshold has been crossed (roughly 5-10 flies per trap per day depending on variety and end use). Options that fit organic rules are mass trapping with attractant traps at the recommended density, often one to two per tree placed in the canopy; protein hydrolysate bait sprays on a coarse setting on part of the canopy, provided the formulation is permitted; kaolin clay as a physical barrier; early harvest; and removal of fallen and infested fruit. Re-check traps twice weekly and record catches, because that record is what justifies each intervention and demonstrates that the threshold, not habit, drove the decision.
2. Given the copper already applied, decide how to handle the olive leaf spot for the rest of the season.
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Copper is permitted but capped: EU rules set a maximum of 28 kg/ha over seven years, an average of 4 kg/ha/year, and national or control-body limits may be lower. At 3.2 kg/ha already used, only about 0.8 kg/ha remains in this year's budget, and the seven-year average must still be respected. A further full copper spray would breach the budget.
Manage leaf spot with pruning to open the canopy, removal of heavily infected leaves and timing sprays to the high-risk autumn and winter period rather than a fixed 10-day calendar. Use the lowest effective rate and a formulation that adheres well. Keep a copper ledger per plot showing product, rate and date, because the inspector will reconstruct the seven-year total.
If pressure is high, accept some leaf spot: for oil production, fruit fly damage costs far more quality than moderate leaf spotting. Do not let the leaf-spot concern push the copper budget over the limit or delay the fly and harvest decisions.
3. Advise on harvest timing and post-harvest handling to protect oil quality under this fly pressure.
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Harvest earlier rather than later. Oil content rises into November, but fly damage and autumn rain raise free acidity and peroxides, and that quality loss outweighs the extra oil. Sample fruit weekly; when 10-20% of fruit show active infestation, or catches remain high, start harvest.
Pick into vented crates, do not compact the fruit, and deliver to the mill within 24 hours, preferably within 12 in warm weather. Do not mix fruit collected from the ground with tree fruit. Mill at low temperature, and store oil in stainless steel, in the dark, cool and with low headspace.
Record harvest dates and lots so that any fly-damaged oil can be traced and segregated. If part of the crop is heavily infested, keep it separate and press it promptly rather than blending it with clean fruit; blending spreads the quality defect across the whole lot.