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A chilli farmer in Andhra Pradesh reported 60% flower drop despite good irrigation and nutrition. Soil tests showed NPK was adequate. The missing element: boron — applied at just 1–1.5 g/L at flowering, yields nearly doubled in the next season.
Boron is the micronutrient with the narrowest sufficiency range of any element — too little causes flower drop and poor fruit set; too much is toxic. Getting it right is critical.
Symptoms of Boron Deficiency in Chilli
- Flower drop — buds form but drop before opening. Most visible symptom.
- Poor pollen viability — flowers that don't drop still don't set fruit because pollen is sterile
- Thick, brittle, curled leaves — young growth looks abnormal
- Hollow stem — cut the main stem and see air pockets inside (common in cauliflower too)
- Tip dieback — growing tip blackens and dies in severe cases
- Fruit cracking — irregular cell development causes fruit walls to crack
Why Boron Deficiency Occurs in Chilli
Boron is most commonly deficient in:
- Sandy, light-textured soils — boron leaches easily with irrigation/rain
- High rainfall areas — continuous leaching depletes boron
- Acidic soils (pH <6) — boron becomes less available
- High calcium soils — calcium and boron compete; high Ca reduces B uptake
- Dry spells during flowering — boron moves to roots with water; dry soil = no B movement to flowers
🔍 Soil test for boron: Hot water extractable boron. Deficient if below 0.5 ppm. Most sandy soils in AP/Maharashtra run 0.2–0.4 ppm — deficient range.
Which Boron Product to Use
| Product | Boron % | Best Use | Notes |
|---|
| Boron 20% WSP | 20% | Foliar + Drip | Best for flowering spray — fast absorption |
| Calcium Boron Liquid | B:2% Ca:8% | Foliar | Combined Ca+B — ideal for chilli/tomato |
| Borax 11% | 11% | Soil basal | Pre-planting soil application |
| Boric Acid 17% | 17% | Foliar | Alternative to Boron 20% WSP |
Correct Dose and Critical Timing
For Chilli/Capsicum (Foliar)
- Rate: 1–1.5 g/L (Boron 20% WSP) or 2.5 mL/L (Calcium Boron Liquid)
- Timing 1: At bud initiation — when first flower buds appear (before any drop)
- Timing 2: At 50% flowering
- Timing 3: 10 days after second spray
- Total: 3 sprays per crop season
⚠️ Do NOT apply boron when it is hot (above 35°C) — spray early morning or evening only. High-concentration boron under hot sun can cause leaf burn.
For Soil Basal (Borax)
- Rate: 0.5–1 kg/acre Borax 11%
- Timing: Mix with FYM, apply 2 weeks before transplanting
- Caution: Do NOT exceed 1 kg/acre — boron toxicity at higher doses
Boron Toxicity — How to Avoid
Unlike most nutrients, excess boron is toxic. Symptoms: leaf tip and margin burn (similar to salt burn), starting on older leaves.
- Never exceed 2 g/L in foliar spray
- Never apply more than 1 kg/acre as soil basal Borax
- Space sprays 10–12 days apart minimum
- If yellowing/tip burn appears after boron application — flush soil with water immediately
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