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Post-harvest chemical treatment and cooling of apples

This section of the Guide has changed significantly since the first edition was produced in 2001. At that time a number of fungicides were registered for use on apples as a post-harvest dip or drench. These included formulations of carbendazim and thiophanate-methyl and a mixture of carbendazim and metalaxyl.

There are currently no fungicides registered in the UK for post-harvest application to apples (although, for pears, iprodione still has off-label approval for dipping or drenching).

Several factors have contributed to this situation. The main factor has been public concern over the use of pesticides and chemical residues in food at the time of consumption. Clearly the general public does not appreciate the concept of MRLs  and wants no detectable pesticide on the food when it is eaten.

A second important factor has been the realisation that the application of fungicides to apples after harvest has only a limited effect in reducing fungal spoilage. More effective control of rots can be achieved by chemical intervention in the orchard to prevent initial infections and much can be done with a non-chemical approach. Other factors of concern about post-harvest fungicide use include the problems associated with disposal of drench solutions.

Information on the post-harvest application of fungicides is no longer relevant since there are no products approved for this use in the UK.

The remainder of this section is relevant to the post-harvest application of  calcium for control of bitter pit and other calcium deficiency disorders.


Post-harvest application of  calcium products

Only treat fruit post-harvest with a calcium product where a significant risk of fruit losses has been identified. Place fruit in a store where the fabric, including the floor has been cooled down to below the final holding temperature. The following advice should be adhered to in order to restrict the use of calcium products where possible and to ensure the most efficacious treatment of consignments of fruit where this is deemed to be necessary.

  • Avoid the unnecessary application of calcium treatments by estimating the risk of disorders developing in the fruit during storage.


Calcium treatment for bitter pit

  • Assess the requirement for post-harvest calcium application by taking samples of fruit for mineral analysis 2 weeks prior to harvest.   Where calcium levels are lower than those recommended, calcium treatment is advisable.
  • Do not exceed the suggested dose for any calcium product as damage to the skin may result. Only treat cultivars that are listed on the product labels.
  • Post-harvest calcium treatments should be applied only to cultivars that are susceptible to calcium deficiency disorders, for which pre-harvest fruit analysis will indicate the need for supplementing calcium concentration.


Staff training and certification for post harvest treatment

  • Growers should be aware of the legal requirements regarding operatives involved in the drenching or dipping of fruit with chemicals.
  • All contractors or staff born after 31 December 1964 who apply pesticides must have attended and passed a National Proficiency Test Council (NPTC)-recognised course in ‘The Safe Use and Handling of Pesticides (PA1)’, together with courses for the relevant piece of machinery (PA10 for drenchers).
  • Those who are operating under the so-called ‘grandfather rights’ will need to produce a certificate of attendance at a recognised i.e. NPTC training course both in the Safe Use of Pesticides and the Post-Harvest Application of Pesticides.


Equipment calibration for post harvest treatment

The following procedures should be adopted for calibration:

  • Measure volume of tank.
  • For square tanks calculate volume = height x length x width.
  • For round tanks calculate volume = radius x radius x height x 3.142.
  • For measurements in metres multiply volume (cubic metres) by 1000 to provide volume in litres.
  • For measurements in feet multiply volume (cubic feet) by 6.24 to provide volume in gallons.
  • Measuring jugs and scales should be specific for the job and not used for any other purpose.


Good practice preparing for post harvest treatment

The following procedures should be adopted for operation:

  • Mark the tank to show the operating level (full).
  • Add clean water until the tank is approximately three-quarters full.
  • Use a clear area to weigh or dispense chemicals.
  • List chemicals and quantities used in each tank mix.
  • Dilute the concentrate in the ratio of 1 part chemical to 9 parts water. Always cream wettable powders in water before adding to the tank.
  • Add to the tank and fill to the mark. Mix for at least 10 minutes.
  • Label tank clearly with contents.
  • In order to prolong the life of the solution any soil should be removed from the outside of bins to prevent soiling of the yard and of the drenching/dipping solution.
  • Separate the bin reception area from the standing area for treated bins.


Good practice during post harvest treatment

  • Treat fruit for 60 seconds maximum.
  • Fruit should not be treated above 210C or below 100C (optimum 160C).
  • Top-up using solution diluted to the correct concentration.
  • Change solution every 2 or 3 days or when excessively dirty. DPA manufacturers suggest refilling with fresh solution after every 100 bins.  This may be fewer than are treated in practice, particularly where dip tanks are used.


Good practice following post harvest treatment

  • Dispose of the used (dilute) solution  on an area of land authorised for the purpose by the Environment Agency, via a licensed waste disposal company or by the use of equipment designed specifically to treat waste pesticides.
  • After chemical treatment allow the fruit to drain  before stacking into a store that has been cooled thoroughly prior to loading.
  • Stores with insulated floors should be pre-cooled for 5 days and those with un-insulated floors for 10 days.
  • Ensure that the refrigeration plant is switched off during loading. Use other available stores for pre-cooling fruit prior to loading.
  • Ensure that fruit reaches the final holding temperature within 5 days of the start of loading.