Pruning and crop manipulation workshop – key points

Pruning and crop manipulation workshop

27 July 2018

Earlier this month, Citrus Australia – South Australia Region (CASAR) held a pruning and crop manipulation workshop hosted by the Mildura Fruit Company (MFC) for citrus growers in Waikerie and Lyrup, SA.

Kerry Robertson organised the event that attracted 90 growers to listen to MFC’s Spanish consultant John Chavarria discuss the most important crop manipulation strategies according to the different growth stages of the tree. Kerry and CASAR Chair Steve Burdette summarised some of the key points shared during the workshop as displayed in the table below.

NOTE: Grower orchards and properties can vary – any crop manipulation technique should always be trialled first for a couple of years before being implemented on farm.

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Winter (crop manipulation)

• GA 10 ppm during June/early July (1st sensitive peak)
  • Differentiation flowers versus vegetative growth (limits flowers)
• GA 5-10mm at 2mm bud break (2nd sensitive peak)
  • Limits flowering and stimulates vegetative growth.

Winter (increase flower induction)

• Urea and phosphonate (without fruit on trees) – potential MRL issue / Urea and Zinc & Manganese (with fruit on trees) from July to bud induction
  • Important to consider if you do a colour break GA to extend harvest.
  • Increases flower induction.
  • Caution using urea on trees in frost sensitive orchards.
  • Caution against exceeding the phosphonate MRL.
  • Monitor the pH because if it drops it can cause burn.

Fruit set

• GA navels and Afourer mandarins to improve fruit set- apply 1-2 x 10-20ppm at 90% petal fall
  • Number of sprays depends on blossom density and spread

Fruit thinning

• Two auxins can be used 2,4DP and Tops
  • Follow labels carefully – both products can be used at different timings for either thinning and/or sizing

Rind integrity

• GA 10-20ppm from late December to early January
  • Can apply calcium (important during cell division) and potassium as a foliar spray from bloom to early January (boron can also be applied with calcium).

Delayed harvest

• 10ppm GA at colour break
  • At 95% colour break the delay effect is less.
  • Chinese consumers prefer firm fruit.
  • Stop drop can be used but caution against MRL for Korea – 10ppm should be fine.

Pruning

• Small trees up to year two – no pruning
• Shape canopy and remove suckers from year three.
• Navels: window prune 15-20% of the canopy to encourage light penetration at a 45-35° angel not in the rows.
• Afourer: cut central limb to open up the tree from 1 to 3 years of age. Afourer crops on the tips and crop set becomes a challenge from year 10 onwards.
• Comments:
  • Some pruning is better than no pruning.
  • Supervision of contract pruners is important.
  • Trial and adjust pruning techniques regularly.

Imperial Mandarins

• Where water mark is an issue try 5ppm GA at colour break (be cautious of timing crop regulation and potential rind damage)
  • pH 6 in winter is important.
  • Do not spray too early or late in the day.
  • Apply a small droplet with good coverage
  • Buffer the spray but do not use a wetter.

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The above is merely a guideline and it is important for growers to get professional advice before applying some of these crop manipulation strategies. The choice of strategy will depend on whether the tree is in an ‘on’ or ‘off’ year cycle, tree condition, age, etc.

Some other useful tips included to 1) test a new strategy out on a row or two in the first year to see how it might work with the planted variety; 2) don’t increase flowering, fruit set or thinning on young trees; and 3) only apply GA during summer (golf ball size) for late navels.

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Acknowledgement

Thank you to Mildura Fruit Company’s Bill Robinson and Justin Lane for additional technical input.