Tomato with flower drop, blossom-end rot and fruit borer

Diagnosis

• Sustained 36–39°C days with warm nights is the dominant cause: above about 32°C, pollen viability falls, anther dehiscence fails and the style elongates past the pollen tube, so fruit set collapses regardless of nutrition.
• Rank growth from 150 kg/ha of urea already applied has pushed carbohydrates into leaves rather than flowers, adding to the drop.
• Moisture stress compounds it. Assume 22,000 plants/ha at 75 × 60 cm with 4 L/h drippers: 20 minutes = 1.33 L/plant/day = 29.6 m³/ha = a little under 3 mm/day, against a crop demand near 6 mm/day. He is irrigating at roughly half of requirement.

Verdict: no urea. More nitrogen worsens both the drop and the blossom-end rot risk by competing with calcium and driving vegetative growth.

Priority for seven days: stop nitrogen, increase drip duration to about 40–45 minutes daily delivered early morning, and give a light mulch to cool the root zone. Accept that the current truss is largely lost and protect the next flush - set will recover when night temperatures fall. Do not spend money on calcium sprays for the drop.

Why foliar Ca fails: blossom-end rot is not a soil calcium shortage here. At pH 7.4 with a sandy loam, soil Ca is adequate; the failure is in delivery. Calcium moves only in the xylem, follows the transpiration stream to leaves, and reaches the fruit poorly because fruit transpire very little. A spray wets the fruit skin and cannot supply the distal tissue that is dying. The disorder is driven by fluctuating moisture and by high salinity or sodium in the root zone reducing water uptake.

What actually works

• Steady moisture: shorter, more frequent drip cycles so the root zone never dries and then floods; check emitter output and wetting depth with an auger.
• Do not lime - pH 7.4 already limits micronutrient availability; excess lime would worsen Zn/B supply.
• Check the water for sodium and chloride, not just EC. EC 1.6 is workable, but if Na is high, blend with rainwater or leach slightly.
• Reduce ammonium nitrogen and avoid excess K and Mg, which compete with Ca uptake.
• Remove badly affected first-truss fruits so the plant does not spend on unmarketable sink; later trusses under better moisture usually show less BER.

Judge success by the percentage of BER on the fourth and fifth trusses after the changes.

Why the current plan fails

• Spraying every fourth day selects resistant borer populations and removes natural enemies, which triggers rebound infestation.
• Pyrethroids have short residual and, more importantly, the repeated schedule risks picking fruit inside the pre-harvest interval (PHI).

Revised plan

• Now (10 days before picking): hand-pick and destroy all bored fruits and fallen fruit twice a week; this removes the larvae the spray cannot reach.
• Install pheromone traps at about 20/ha to monitor adult flight and time any spray to egg-hatch, not to the calendar.
• Choose one product with a label PHI that fits the picking date and a different mode of action from the pyrethroid - for example chlorantraniliprole 18.5% SC at 0.3 ml/L (PHI about 3–5 days) or emamectin benzoate 5% SG at 0.4 g/L (PHI about 5 days). Spray in the evening, wetting the underside of leaves.
• Stop all sprays at least 5 days before the first picking; record product, dose and date for the buyer's residue assurance.
• Rotate to Bt or HaNPV for early instars in the following flush to slow resistance.

Any insecticide applied inside its PHI can make the whole 0.4 ha unmarketable - the harvest calendar, not the spray interval, must set the schedule.