Maleic Hydrazide for Onion: A Practical Guide to Pre-Harvest Sprout Control

Maleic hydrazide (MH) is a plant growth regulator used on onions at the pre-harvest stage to suppress sprouting during storage and long-distance distribution. When applied in the correct field window and paired with sound storage management, MH reduces sprout initiation, weight loss, and soft rot risk, helping maintain marketable quality and extend the saleable period.

What Is Maleic Hydrazide?

Maleic hydrazide is a plant growth regulator that primarily inhibits cell division (mitosis) rather than cell expansion. In onions, its commercial value is simple: delay or suppress bud activity in bulbs after harvest so they remain saleable longer through warehousing, transport, and seasonal carryover.

Key identifiers (for documentation and procurement):

• Common name: Maleic hydrazide (MH)

• Functional class: Plant Growth Regulator (PGR)

• Typical use on onions: Pre-harvest foliar application to reduce post-harvest sprouting

• Compliance: Subject to destination-market regulations and MRLs (maximum residue limits)

Note: Always follow the registered label and local regulations. This document explains principles and management—not step-by-step operational directions or dosages.

Onion Physiology and Why Sprouting Happens

Onion is a bulb crop. After harvest, bulbs remain physiologically active. Under favorable conditions (temperature, humidity, oxygen), dormant buds can re-activate, leading to sprouting, weight loss, textural changes, and higher sorting downgrades. These outcomes increase claims, rejections, and downstream waste, especially on long logistics chains.

How MH Works on Onion Bulbs

• Mode of action: MH reduces meristematic cell division at bud sites, delaying the physiological processes that drive post-harvest sprout initiation.

• Effect dependencies: Response varies by cultivar, field maturity, application timing, canopy coverage, and post-harvest storage parameters.

• Expected outcomes (when used correctly): lower sprout incidence, reduced physiological weight loss, improved visual grade consistency, and longer market window.

MH is an enabler, not a substitute for storage discipline. It curbs the biological drive to sprout; storage controls curb the environmental drivers that accelerate deterioration.

Application Window and Field Discipline (Principles Only)

Objective: maximize sprout suppression while minimizing quality risks.

• Maturity signal: Apply near physiological maturity prior to harvest (e.g., when tops naturally lodge and necks begin to dry).

• Window discipline: Too early → diminished return and residue inefficiency; too late → weaker sprout control and logistics friction with harvest operations.

• Coverage logic: Aim for even canopy coverage; pay attention to the neck/leaf-sheath transition area to avoid untreated pockets or excessive overlap.

• Traceability: Record maturity markers, field blocks, application batches, storage locations, and inspection results to build a farm-to-storage performance baseline.

This guide does not provide dosage or tank-mix recipes. Use only as permitted on the product label.

Storage Integration: MH Is Not a Cold-Store Replacement

High-performance onion programs align pre-harvest MH with post-harvest hygiene and climate control:

• Temperature and relative humidity within target ranges

• Ventilation and airflow design through bins/pallets

• Sanitation, sorting, and adequate neck drying before storage

• Monitoring (sprout checks, weight sampling, soft-rot observation) and corrective actions

Treat MH as part of a system: field window → curing/drying → grading → climate-controlled storage → periodic QC checks. When these steps line up, losses drop in a repeatable way.

Quality and Commercial Outcomes

Physical/visual: delayed bud emergence; more consistent grading
Physiological: reduced dry-matter loss linked to sprouting and respiration
Microbial risk: correct timing and good storage practices lower soft-rot risk; misuse (off-window/over-application) can raise it
Financial: less shrink + longer saleable window + fewer claims = more predictable margins, especially for export programs and seasonal carryover

Risk and Compliance

• Label boundaries: Respect timing and any use restrictions. Deviations can reduce efficacy or heighten rots.

• MRLs: Destination markets may differ. Align pre-shipment documentation, sampling, and third-party testing with buyer and regulatory requirements.

• Compatibility: If aligning with pre-harvest fungicide programs, manage sequence and compatibility; avoid unsanctioned tank mixes.

• Data integrity: Maintain batch records, retain samples as required, and standardize inspection forms.

Procurement and Technical Documentation Checklist

• Product identity: Maleic hydrazide (intended for onion sprout control)

• Regulatory fit: Registration status and MRL acceptance for target markets

• Documentation: COA, MSDS, label in applicable languages

• Storage program alignment: Temperature/RH targets, airflow plan, sanitation SOPs

• Traceability: Lot numbers, application dates, storage locations, inspection cadence

Frequently Asked Questions

Q1. If MH is used, is cold storage still necessary?
Yes. MH reduces the biological impulse to sprout; temperature, humidity, and airflow management reduce environmental drivers. Both are needed for consistent low-loss outcomes.

Q2. Why is the “timing window” emphasized so much?
Because early/late applications dilute return on investment and can shift risk (e.g., weaker sprout control or higher soft rot). Window discipline governs program success.

Q3. Does MH change flavor or consumer perception?
Within label limits and correct timing, the objective is quality stability, not sensory alteration. The net effect is typically improved saleability due to lower sprouting and better grade consistency.

Q4. Do all onion cultivars respond the same way?
No. Response can differ. Pilot on representative blocks first, then scale once a cultivar–window–storage baseline is established.

Q5. Can MH be tank-mixed with other inputs?
Only as permitted on the label and after evaluating compatibility and sequencing. When in doubt, separate operations and follow official guidance.

Conclusion

Maleic hydrazide is a proven lever for pre-harvest sprout suppression in onions. Its value compounds when it is timed correctly, applied evenly, and integrated with disciplined storage management. Treat it as a system component—pairing biological control of sprouting with environmental control in storage—to deliver repeatable quality and more predictable commercial outcomes across long supply chains.