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Producing apples with minimal residues

Background

Today’s consumer has high expectations for perfect, blemish-free fruit that are also free of crop protection product residues. Several important retailers in the UK have responded to this expectation and are asking their suppliers to strive towards elimination of residues from fresh produce including apples, to maintain and improve consumer trust.

The incidence of detectable residues has declined, as post-harvest treatments are no longer frequently used, but considerable further adjustment of pest and disease management practices is needed to meet customers’ future requirements.

However, the main UK apple varieties Cox, Gala, Braeburn and Bramley are susceptible to all the major pests and diseases and the UK climate ensures that one or other of these problems is significant in most seasons. So to produce perfect apples that are also free of crop protection product residues is a very high expectation. The challenge is therefore to develop crop protection systems that satisfy the consumer, but that are also profitable and sustainable for the grower. There are two approaches to producing apples free of residues:

  1. Extending the harvest interval of crop protection products used in the post-blossom period to ensure residue free.
  1. Not using conventional products after petal fall i.e. zero residue management system (ZRMS).

In some high pest and disease risk seasons a combination of the two approaches may be necessary.

Determining harvest intervals for zero residues

Statutory harvest intervals are designed to ensure that residues in harvested fruit are below the maximum residue level (MRL) and not to ensure that levels are so low that residues cannot be detected and reported. Data on available residue degradation for each product / crop combination can be obtained from agrochemical companies and the information used to estimate a suitable pre-harvest application interval likely to produce zero residues.

Information from agrochemical companies or producer co-ops on likely harvest intervals to minimise the risk of reportable residues (RL) in apples for products commonly used post blossom

Active ingredient

Product example

Statutory harvest interval (days)

Suggested harvest interval (days) to avoid residues

methoxyfenozide Runner

14

28

pirimicarb Aphox

3

?

penconazole Topas

14

14 (If 3 sprays only used)

thiacloprid Calypso

14

21

bupirimate Nimrod

14

14

captan Captan 80

14

?

chlorpyrifos Alpha Chlorpyrifos

14

60

myclobutanil Systhane

14

14 (residues rarely above RL)

 

Adopting this approach alone and extending the harvest interval to ensure that any possible residues have declined to zero by harvest will reduce the incidence of residues, but complete elimination cannot be guaranteed as the retention of residues is very much affected by seasonal weather conditions. In addition, consideration has to be given to alternative ways of controlling the pest and disease problems that the late season product sprays were targeted against.

Zero residues management system (ZRMS)

The aim of a ZRMS is to reduce residue levels to below the limit of detection by avoiding the use of traditional crop protection products during the period of apple development from post-bloom to harvest and use cultural, biological and other non-conventional methods during apple development instead. The use of conventional products is restricted to the period from post-harvest to petal-fall.

The key feature of the zero residue system is to reduce the populations of pest and disease during the dormant season to ensure negligible inoculum carry over from one season to the next.  The key factors, vital to success are:

  • Choice of suitable orchards
  • Starting at the right time
  • Implementation of the management programme
  • Meticulous and sustained orchard monitoring

Choice of orchard

It is important that orchards selected for zero residues programmes have a low incidence of pests and diseases, especially powdery mildew, at the outset.

  • Those with a history of disease or pest problems should be avoided.
  • The orchard must be well managed and trees trained and pruned to ensure an open canopy for good air circulation and spray penetration.
  • Trials experience so far has been on Cox, Gala, Red Pippin, Braeburn and Bramley and on scab resistant cultivars where there has been good success.
  • It is important  not to be too ambitious initially.
  • Select one or two orchards on the farm to manage according to the system to gain experience before embarking on a wider adoption of the system.

When to start

  • It is important to start the ZRMS in the autumn, shortly after harvest to implement the important late season and dormant period tasks that are vital to success.

Zero residues management

Pest and disease control

There are numerous potential pest and disease problems that must be addressed in order to produce marketable fruit.  The features of the zero residue management treatment system are summarised in the table below, starting immediately after harvest.

Summary of treatments in zero residue programme  

Timing

Pest / Disease target

Treatment

Post harvest (conventional crop protection products)
September / October scab / mildew Systhane + Captan
October Nectria canker Fathom*
October (approx. 7-14 October) aphids Aphox or other aphicide but from a different chemical group to Calypso
Pre leaf fall scab urea
Leaf fall Nectria canker Cuprokylt / Fathom*
Winter overwintering codling Nematodes
Winter Nectria canker Removal in pruning
Winter / spring scab Macerate leaf litter
Pre bud burst (conventional products)
Spring scab / Nectria canker Cuprokylt
Bud burst – petal fall (conventional products)
Bud burst – petal fall scab Dithianon / Captan / Systhane
Budburst – petal fall mildew Systhane or Topas
Mouse ear / green cluster tortrix / winter moth Runner
Pink bud tortrix Insegar
aphids / weevils / sawfly / capsids Calypso
Blossom and petal fall Nectria / storage rots Bellis or Captan or Switch
Petal fall tortrix / codling moth Insegar
aphids / weevils / sawfly / capsids Calypso
Petal fall – harvest (sulphur, biocontrol or cultural control only)
Petal fall – harvest mildew sulphur
Petal fall – harvest codling moth Granulosis virus
Petal fall – harvest tortrix Dipel* (Bacillus thuringiensis)
Petal fall – harvest storage rots Rot risk assessment / Inoculum removal / Selective picking

*  EAMU

Management of the herbicide strip

Management of the bare herbicide strip beneath the tree should be the same as in conventional production.

  • Excessive weed growth is undesirable but, if carefully managed, could provide soil cover to prevent soil splash to fruit pre- harvest.
  • A dead grass mulch is ideal.
  • Applying a straw mulch would also prevent soil splash.

Orchard monitoring

A rigorous, regular programme of orchard monitoring for pests and diseases is vital. This enables timely corrective action to be taken.

  • Orchard inspection for scab during blossom and petal fall is critical.
  • If significant levels of scab are present then proceeding with the zero residues programme is not advised.
  • Similarly, if a problem gets out of control between petal fall and harvest then it may be necessary to make conventional product applications to make a correction.
  • This should rarely be necessary and may not result in residues if a sufficiently long harvest interval can be observed.

Starting out with minimal residues production

  • Try the ZRMS system on a few orchards initially.
  • Choose orchards with a low incidence of pest and disease.
  • Start the system post-harvest in the autumn so that dormant season treatments have been implemented to minimise the pest and disease carry over.
  • Rigorous pest and disease monitoring is essential so ensure that suitable qualified personnel are committed to doing it.
  • Inspections for apple scab at blossom and petal-fall are critical in order to decide whether to proceed with the ZRMS programme or continue conventionally so ensure that they are made.
  • Ensure that pest and disease monitoring from petal-fall to harvest is undertaken to spot any potential problems early in case treatment intervention is needed.
  • For scab susceptible varieties or in orchards in areas of high rainfall or in high risk seasons, a more flexible approach may be required and the use of conventional control programmes may need to be extended for a couple of spray rounds after petal fall to ensure adequate control is achieved.
  • For powdery mildew, in high risk situations, additional spray rounds beyond the end of petal fall would be necessary to provide improved control and fungicide dose and spray interval may need to be adjusted accordingly.
  • Based on research findings, growers following this system can be more relaxed about the incidence of rots in store, but rot risk assessments in orchards should be made routinely leading up to harvest. The AHDB Horticulture Rot Risk Assessment training DVD should be employed to teach staff how to make such assessments.
  • For pest control, particular attention should be reserved for woolly aphid and mussel scale. For these pests, there may be a need to extend conventional control programmes beyond petal fall and then to extend the harvest interval to be sure of avoiding residues.
  • If conventional product intervention post petal fall proves to be essential for any pest or disease, then extending the harvest interval of products used in this post-blossom period will help to ensure minimal residues or residue free fruit.