Spray decision at flowering: downy mildew, powdery mildew and grape moth
On 10 May, a 1.2 ha Xynisteri block at 500 m near Paphos is at BBCH 57-65 (inflorescences separating to full flowering). Pheromone traps for Lobesia botrana caught 28 moths per trap per week, up from 6 the previous week. After 25 mm of rain on 6-7 May, downy mildew oil spots are visible on about 8% of leaves in the lower canopy, and a few sporulating lesions are on the shaded side. Powdery mildew is present on about 2% of inflorescences. The forecast is 32-34 C and sunny for the next five days. The grower plans a single tank mix of copper oxychloride (2.5 kg/ha), a pyrethroid for the moth and wettable sulfur (3 kg/ha), applied at midday, and wants to repeat it every 7 days until harvest in early September. Adjacent parcels include a certified organic vineyard and a beehive area.
1. Evaluate each of the three pest problems and justify treatment or no treatment, with timing and thresholds.
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Downy mildew. Eight percent oil spots with sporulation in the lower canopy, after 25 mm of rain at flowering, is not a wait-and-see situation. Flowering inflorescences are highly susceptible, and oil spots are an established infection, not a warning. Copper alone is a protectant; it does not cure existing lesions. Use a systemic or curative partner (for example fosetyl-Al, dimethomorph or mandipropamid, rotated by FRAC group) plus a protectant cover.
Powdery mildew. Two percent of inflorescences at flowering is above the usual treat-now level, and this is the most damaging window for the crop. Sulfur is effective, but only when temperatures stay below about 30-32 C; with a 32-34 C forecast, midday sulfur risks leaf and bunch burn.
Lobesia botrana. Twenty-eight moths per trap per week is high, but a trap count alone is not a spray decision. Inspect 100 inflorescences for eggs and larvae and look for damage from the previous generation. At flowering, Bacillus thuringiensis or mating disruption is preferable to a pyrethroid because it spares natural enemies and bees; a pyrethroid at flowering would also kill pollinators.
Priority: downy and powdery mildew at flowering are the two that can cost the crop; the moth is a monitoring and selective-treatment issue, not an automatic spray.
2. Critically assess the proposed tank mix and application practice. Propose a compliant, resistance-managed programme, including pre-harvest intervals, records and safety.
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Problems with the plan
- Copper oxychloride 2.5 kg/ha is about 1.25 kg metallic copper. Repeated weekly for months, it exceeds the EU limit of 4 kg Cu/ha/year (and 28 kg over 7 years) very quickly.
- Copper plus sulfur can be phytotoxic and is best avoided, especially at 32-34 C. Sulfur burns foliage in heat, and midday spraying increases evaporation, drift and leaf damage.
- A pyrethroid at flowering kills bees from the nearby hives, harms predatory mites and parasitoids, and selects for pyrethroid resistance in L. botrana. Seven-day repeats until September are exactly the resistance-management failure to avoid.
- A pyrethroid applied in late August may still be inside its pre-harvest interval at an early-September harvest, and residues must stay below the MRLs.
- Drift onto the certified organic neighbour is a compliance and liability issue.
A compliant programme
- Spray at dusk or early morning, never at midday in a heatwave.
- Downy mildew: a protectant plus a systemic partner, rotated by FRAC group and within the label's maximum number of applications.
- Powdery mildew: sulfur only when below 30 C, otherwise a registered alternative with a different mode of action.
- Moth: Bt or mating disruption, with trap and cluster counts rather than calendar sprays.
- Check every product's PHI against the harvest date and keep the number of applications per active substance within label limits.
- Record date, product, dose, area, weather, operator and PHI; wear the label PPE, respect re-entry intervals and warn the organic neighbour before spraying.