Powdery mildew and hoppers in a mango orchard supplying an export packhouse
Anita Mohapatra owns a 1.0 ha mango orchard of cv. Amrapali (12 years old) in Dhenkanal, Odisha. The orchard flowered in the first week of January. Since flowering, she has sprayed carbendazim 50 WP twice and imidacloprid 17.8 SL once, on a dealer's advice, at 10-day intervals. Now, at the pea stage, she sees white powdery growth on panicles and young fruit, and hoppers are thick on the flower stalks; some fruitlets have brownish scars. She plans another round of carbendazim + imidacloprid and wants to add a synthetic pyrethroid for hoppers. Harvest is expected in May, and she wants fruit suitable for a nearby export-grade packhouse that tests residues. The orchard has a strong pollinator population, and she keeps two bee boxes. Day temperatures are 32–35°C. She asks whether more sprays will improve fruit set.
1. Diagnose the disease and pest problem and explain the significance of the pea stage for management and for pollinators.
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The white powdery growth on panicles and young fruit is powdery mildew (Oidium mangiferae); the hoppers on flower stalks and brown scars on fruitlets indicate mango hopper (Idioscopus spp.). At the pea stage, fruit set has already occurred, so the priority is to protect the retained fruitlets and prevent further hopper damage, not to increase the number of flowers. The pea stage is also sensitive for pollinators: bees are still foraging, and many pyrethroids and some neonicotinoids are highly toxic to them. Spraying during full bloom or in the morning when bees are active can reduce pollination and leave residues. Day temperatures of 32–35°C increase the risk of phytotoxicity and rapid evaporation, so spray timing and dose matter.
2. Design a spray schedule from now to harvest that addresses powdery mildew and hoppers while respecting residue and pollinator concerns. State what not to do.
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From now to harvest, use a rational, residue-conscious schedule. First, stop repeating carbendazim; it has been used twice and resistance is likely. For powdery mildew, rotate to a different mode of action - for example wettable sulphur, hexaconazole or a strobilurin-labelled product - at the label dose, and spray in the late evening when bees are not flying. For hoppers, use a single recommended product with a known PHI; if the population is below the action threshold, use neem oil or a sticky trap rather than an insecticide. Do not add a synthetic pyrethroid: it is broad-spectrum, toxic to bees and natural enemies, and likely to flare mites. Close or move the bee boxes during spraying and reopen after the spray has dried. Observe the PHI for every product, keep a spray diary, and stop spraying well before harvest. More sprays will not improve fruit set.
3. How would you evaluate her claim that more sprays will improve fruit set? Give an extension message.
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Her claim is not supported. Fruit set in mango is determined by flowering, pollination and weather during bloom; once the pea stage is reached, additional fungicide or insecticide sprays protect the crop but cannot create more fruit. Over-spraying raises cost, residue risk, resistance and bee damage. The extension message: scout, use thresholds, protect pollinators, rotate modes of action, and follow PHI; a healthy canopy and good pollination are worth more than a spray calendar. If the packhouse tests residues, a rejected consignment would wipe out the benefit of any extra spray.