Paclobutrazol or Pruning in an Alternate-Bearing Mango Orchard
A 1 ha Dashehari mango orchard at 6 m × 6 m (278 trees) is 12 years old. Last year it carried a heavy crop of about 80 kg/tree; this year flowering is sparse and the canopy is dense, with about 30% of the inner branches shaded. Soil tests show pH 7.8, EC 0.3 dS/m, organic carbon 0.35%, low available N, medium P and medium K. The farmer plans to apply 2 kg urea per tree in July, flood-irrigate heavily, and spray 1,000 ppm ethephon in October to force flowering. He has heard that paclobutrazol at 10 g a.i. per tree gives a good crop every year. Fruit fly damage last season was 20%. The local recommendation is 600 g N, 300 g P2O5 and 600 g K2O per bearing tree per year, split into two doses.
1. Evaluate the farmer's plan. What is wrong with it, and what would you recommend for the current 'off' year?
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What is wrong
- 2 kg urea per tree supplies about 920 g N, far above the 600 g N recommendation, and all in one dose. Excess nitrogen after a heavy crop promotes vegetative flushes, shades the fruiting wood and worsens alternate bearing.
- Heavy flood irrigation leaches nitrogen, wastes water and can worsen fruit fly and root problems by keeping the orchard floor continuously wet.
- 1,000 ppm ethephon in October is not a reliable or safe forcing treatment for mango. It can cause defoliation and flower drop, especially if the tree is already stressed after a heavy crop.
- 10 g a.i. paclobutrazol per tree is at the high end and should not be applied as a blanket dose. Soil-applied paclobutrazol is taken up slowly and can stunt trees for more than one season, particularly on light or stressed trees.
Recommendation for the off year
The priority is to restore tree vigour and improve light interception, not to force a crop. Prune the dense inner branches after harvest to open the canopy; remove dead wood and water shoots. Apply well-rotted FYM and a balanced fertilizer based on the local recommendation, with irrigation at basin or drip rather than flood. Use paclobutrazol only on individual vigorous trees that have a healthy canopy, at a moderate dose (about 5 g a.i./tree for a 12-year-old Dashehari), applied as a soil drench around the canopy in October–November. Do not treat weak or sparse trees. Do not use ethephon.
2. Using the local recommendation, calculate the fertilizer requirement for all 278 trees and explain how you would split and place it.
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Total requirement
- N: 600 g × 278 = 166,800 g = 166.8 kg N
- P2O5: 300 g × 278 = 83,400 g = 83.4 kg P2O5
- K2O: 600 g × 278 = 166,800 g = 166.8 kg K2O
Fertilizer materials
Use DAP (18% N, 46% P2O5) for the phosphorus: 83.4/0.46 = 181.3 kg DAP, which also supplies 181.3 × 0.18 = 32.6 kg N.
Remaining N = 166.8 − 32.6 = 134.2 kg N, supplied by urea at 46% N: 134.2/0.46 = 291.7 kg urea.
Muriate of potash at 60% K2O: 166.8/0.60 = 278 kg MOP.
Split and placement
Apply full P and half of the N and K after harvest and pruning in July, in a shallow ring at the canopy drip line, incorporated and watered in. Apply the remaining N and K at fruit set, again in the root zone. Do not place fertilizer against the trunk. If the soil test is low in N, the first split can be slightly larger, but the total should stay near the recommendation. The 20 t of FYM, if available, should be spread in the alleys and incorporated, not dumped in a heap at the trunk.
3. The farmer wants to intercrop the orchard with a rainy-season legume to recover the cost of pruning. Advise him, including fruit fly management.
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Intercropping advice
A 12-year-old orchard at 6 m × 6 m with 30% of the inner canopy shaded will transmit too little light for a productive cowpea or mungbean intercrop. Intercropping is more realistic in the first 3–4 years, before canopy closure. In this orchard, a full-field legume intercrop is likely to produce weak plants and compete with the mango roots for water and nutrients.
A better use of the pruning cost is to chop the pruned branches and spread them as mulch under the canopy, and to grow a short-duration legume only in the open southern strips or along the boundary, where light is adequate. If the farmer insists on an intercrop, choose cowpea, sow it immediately after pruning so it can establish before the mango canopy regrows, and do not fertilize the legume heavily with nitrogen. Incorporate the legume residues as green manure rather than removing them.
Fruit fly management
Sanitation is the first step: collect and destroy fallen fruit every day, because larvae survive in the soil and in dropped fruit. Use pheromone or bait traps, and a bait spray of malathion plus jaggery on the foliage, not on the fruit, starting when the fruit begins to colour. Harvest at the correct maturity rather than leaving fruit to over-ripen. Do not use ethephon to force uniform ripening; it can increase fruit fly attraction and reduce shelf life. Monitor trap catches weekly and record them so the next season's spray timing improves.