1. Maturity Indexing (MI)
Fruit maturity at harvest is the most critical factor influencing post-harvest life, especially for Gala apples, which are sensitive to ethylene. Ethylene stimulates enzymes that break down cell walls, accelerating ripening. Once this process starts, starch breakdown rapidly increases and is irreversible. The main disorders associated with Gala are loss of firmness, mixed maturity, and lenticel breakdown.
Key points:
- Only fruit harvested at the correct maturity can maintain marketable quality for extended periods under controlled atmosphere (CA) or regular storage.
- Gala was traditionally stored for up to 3 months, but is now stored for 3–9 months due to market demand.
- Start maturity indexing 3 weeks before the estimated first harvest date.
2. Harvest Recommendations
Table 1 provides general guidelines for maturity parameters at harvest. Starch breakdown, firmness, and sugar (TSS %) are most used for harvest recommendations. For traditional striped Galas, background colour can also be used, but may be insufficient in some regions/seasons.
Table 1: Maturity Indexing Parameters and Norms for Gala Varieties
| Variety | Firmness (kg/cm²) | Sugar (TSS %) | Acids (g/L) | Starch (%) | Pip Colour |
|---|---|---|---|---|---|
| Gala | >7.3 | 11.2–12 | 3–4 | 20–30 | ½ brown |
- Firmness (11.2 mm tip): Focus on >7.3 kg/cm² for sensitive markets (min. export 5.9 kg/cm²).
- Sugars: 11–12% TSS recommended for sensitive markets.
- Titratable acids: Lower acids reduce storability. Avoid high acids from high nitrogen (e.g., young/vigorous orchards with low crop load).
Table 2: Titratable Acids Range for Gala Varieties
| Low | Optimal | High |
|---|---|---|
| <3 | 3–4 | >4 |
- Pip colour: Minimum ½ brown recommended. In years when background colour and starch breakdown do not correlate, use TSS%, firmness, and pip colour for harvest decisions.
- Starch: 20–30% starch breakdown for 8 out of 10 fruit is optimum.
- Full red (block colour) Gala: Background colour is not always sufficient. Focus on starch degradation, firmness, and TSS%. Sample within the canopy (top/bottom, inside/outside) to assess maturity variation. See BigBucks technical manual for sampling examples.
3. Harvest Management Strategy with Plant Growth Hormones
Plant growth regulators (PGRs) are increasingly used for harvest planning due to these advantages:
- Reduce ethylene production, delaying starch breakdown and ripening.
- Improve harvest management flexibility and weather response.
- Maintain fruit firmness, increase fruit size, and reduce fruit drop.
Recommendations:
- Apply ReTain (AVG) and Harvista (1-MCP) as advised by pre-harvest consultants.
- See Annexure B for a summary of these chemicals.
- Review the BigBucks harvest guideline for the latest ReTain research.
4. Fruit Intake
Split fruit into two groups:
- High-risk fruit for long-term storage (“hot parcels”): Young trees, vigorous orchards (high nitrogen, low calcium, low phosphate), low crop load, or stressed orchards.
- Normal intake.
- Review BigBucks notes for managing heat damage before sorting and packing.
- BigBucks harvesting info
- Deliver fruit within 6–8 hours after harvest.
Field heat:
Lower bin temperature to -1.5°C (corners may reach -1.7°C). Use thermocouples to measure bin centers and monitor cool-down rate. Use good cultural practices to limit temperature fluctuations.
SmartFresh (SF):
Apply within 5 days (max 7 days) after harvest.
5. Storage
- Fill CA rooms per protocol.
- Store high-risk lenticel fruit under RA or short-term CA to allow lenticel breakdown to develop before packing. After breaking CA, wait 10 days before packing for lenticel damage to become visible.
- Manage humidity as high as possible.
- Rank and evaluate CA rooms by ethylene concentration changes.
- Sampling: Take one apple from 20 crates over a 10-week period before storage to account for variability.
- Pre-sorting: Treat fruit with SF first; only pre-sort after SF treatment due to maturity variability.
- Storage regime: Review recommended temperature and gas regimes for Gala in Appendix 2.
6. Packing
- Keep fruit temperature below 12°C throughout packing.
- Do not take more than 20 bins out of storage at a time.
- Coordinate logistics to minimize fruit exposure to higher temperatures during breaks.
- Use bags with micro-perforations.
- Manage time exposed to flumes and drenches (especially during loadshedding).
- Ensure water chemicals are at optimal concentrations.
- Plan PPECB inspections in advance to limit temperature exposure.
- Build pallets in cold storage if possible; forced cooling should start within 90 minutes of pallet building.
- Use perforated bags for forced cooling; aim for optimum temperature within 2–5 days.
- Recommended loading temperature: -0.5°C with closed vents.
Annexure A: Pip Colour Index – GDL AVG (ReTain) Spray Guide Example
- Index value of 2 for GDL (NIVV) = ReTain spray.
- For GDL (NIVV), ReTain sprays are recommended when pip colour reaches 1.8–2.0 (Hortec index).
Annexure B: Plant Growth Regulators and How They Affect Fruit Maturity
Two PGRs are registered in South Africa for apples to interfere with ethylene production and delay ripening: ReTain® and Harvista™. Both are effective but differ in mode of action, timing, and effect.
| ReTain® (AVG) | Harvista™ (1-MCP) | |
|---|---|---|
| Active ingredient | aminoethoxyvinylglycine (AVG) | 1-methylcyclopropene (1-MCP) |
| Mode of action | Binds irreversibly to a key enzyme, blocking ethylene production | Blocks ethylene receptors, making cells unresponsive |
| Main effects | Slows natural ripening, stem loosening, flesh softening, starch disappearance, red colour formation, can reduce watercore and stem-end cracking | Slows starch breakdown, fruit softening, red colour development, pre-harvest drop, can delay watercore onset |
Application:
- ReTain: Apply well before the climactic rise in ethylene. Use full bloom dates and maturity testing (e.g., GDL with >1 generation fruit). Seed colour around 1/3 brown (1.8–2.0 pip analysis) is a good indicator.
- Harvista: Can be applied 21–4 days before expected harvest. Not tank-mixed; requires an inline injection system.
Recommendations:
- Apples (all cultivars): 830 g/ha @ 1000 L water or 83g/100L, 28 days before first pick (ideal for single-pick cultivars like Golden Delicious).
- Royal Gala, Cripps Pink (Pink Lady®), Braeburn: 550 g/ha @ 1000L or 55g/100L, 7 days before first pick.
- To delay whole harvest by 7–10 days.
- Late application helps control maturation rate of later picks.
- Golden Delicious: Spray at 5–10% starch breakdown.
- Royal Gala and Cripps Pink: Spray at 10–15% starch breakdown. In EGVV, trend is to apply earlier (5–10% starch breakdown for first generation fruit).
- To delay whole harvest by 7–14 days.
Warnings:
- Do not use on stressed trees (mites, drought, waterlogging).
- Do not apply with pesticides, other PGRs, or plant nutrients.
- Use an organo-silicone surfactant (e.g., BREAK-THRU® or Silwet L-77® at 50 mL/100L).
- Harvista is applied by a proprietary in-line injector system (contact AgroFresh for info).
Note:
PGR response is highly influenced by weather before, during, and after application. Always record spray date, time, and weather to evaluate PGR influence for each orchard.