https://www.dpi.nsw.gov.au/agriculture/horticulture/citrus

Program:

1. Choice of orange variety

• State the nutritional value of oranges.

• Explain why the Washington Navel variety was chosen for the school orchard.

• State the importance of the citrus enterprise in NSW

2. Management

• Construct a calendar of events for oranges including: fertilizer usage, pest prevention, pruning, harvest, irrigation, disease prevention.

• Identify symptoms of nutrient deficiencies in orange trees.

• Skirting/pruning

3. Pest and diseases

• Outline for a major disease; effect on pest/symptoms, management in a commercial setting

• Outline for a major pest; lifecycle, appearance, effect on plant/symptoms, management in a commercial setting, prevention.

4. Sustainability

• Evaluate two sustainable management practices in the JRAHS orchard

5. Post-harvest treatment

• Describe how technology is applied to oranges post-harvest and the treatment of oranges in preparation for marketing.

6. Marketing  

• Describe the markets the Washington Navel enterprise is trying to meet at James Ruse and in the wider industry.

7. Interactions  

• Draw a systems diagram representing a citrus enterprise.

1. Choice of orange variety

Origins:

• In 1820 a mutated sweet orange tree was discovered in a monastery orchard in Brazil. The fruit had a mutation at the bottom blossom end of the orange with a depression that looks like a human belly button, so it was called a navel orange.

• In 1870 a cutting was sent to Washington, D.C., and the variety was named Washington navel orange.

• Vegetatively propagated.

Benefits of grafting/budding:

• Seedless plants: only method to increase numbers

• Resistant root stocks: provides a clean alternative in the control of soil diseases and pests by using (trifoliata is resistant to root rot)

• Additional vigor: to the plant that can increase quality, number, and size of fruit.

• Improve tolerance: to adverse factors (salinity, lack or excess of humidity), efficient use of water and nutrients and resistance to drought. This allows propagation of fruiting varieties that are not well adapted to local soil conditions or have weak root systems.

• Establishment in a short time: of a plantation for commercial purpose.

State nutritional value of oranges.

Nutritional value of oranges

• Vitamin C: Boosts immune system, healthy gums, prevents scurvy

• Dietary fiber: keeps digestive system regulated

• Vitamin A: good for vision and skin

• Thiamin: (B1) fights fatigue/tiredness

• Calcium: strengthens teeth and bones

Explain why the Washington Navel variety was chosen for the school orchard.

• Suitable climate (cool conditions favored)

• Fruit hold (extended harvesting time)

• Early variety (suitable for school term) (valencia would ripen during school summer break)

• Seedless variety

• Fresh variety (Eaten as fresh fruit) (valencia is juiced)

• Common and easily available as a young grafted tree to plant

Washington navel is being compared to Valencia as they are the two most commonly produced commercial varieties.

2. Management

Construct a calendar of events for oranges including: fertilizer usage, pest prevention, pruning, harvest, irrigation, disease prevention.

Summer

Pest control

• Mineral (white) oil - fornightly (prevents Citrus Leaf Miner attack) (continue for aphids if necessary)

Fertilize

• Dynamic lifter/blood and bone plus

• Epsom salts: magnesium sulfate (for deficiency) (MgSo4 - 2 tbps/9L or 2kg/tree)

• Foliar Spray (Zinc Sulfate, ZnSo4 - 20-30ml/L)

Autumn

• 
  Renew fruit fly lures (wild may baits)

Winter

Harvest

• Harvest after first cold weather/frost

• Collect fallen fruit - daily (reduce disease spread-Blue mould)

Fertilize

• Dynamic lifter/blood and bone plus, applied at the drip line to help overcome nitrogen deficiency. 

• Epsom salts: magnesium sulfate (for deficiency) (MgSo4 - 2 tbps/9L or 2kg/tree), applied twice a year

• Foliar Spray (Zinc Sulfate, ZnSo4 - 20-30ml/L)

Spring

Pest control

• Mineral (white) oil - fortnightly (prevents Citrus Leaf Miner attack) (continue for aphids if necessary)

• Bronze orange bug control (white oil and detergent spray 1L) (large populations: pesticide)

Note:

1. Shoots growing from the rootstock/water shoot + dead wood are pruned off

2. Skirt to 300mm above ground (irrigation height) before flowering

3. Irrigate as necessary except for winter (using soil moisture probe and automatic i-core system)

(total water = 39-49in/year)

Shoots from Rootstock: shoots growing underneath the grow union (from rootstock)

Watershoot: growing from roots underground

20XX Washington Navel Orange Calendar of Operations

Identify symptoms of nutrient deficiencies in orange trees.

nitrogen

• 
  Yellowing of whole leaves (older → younger)

• Premature falling (old leaves)

• New leaves are stunted (small, thin, fragile, and light green)

Magnesium (core of chlorophyll)

• 
  Yellowing with veins still green (older → younger)

• Distinct yellow pattern: Begins bear the edge + towards leaf end

Leaves triangle of green at base

zinc

• 
  Yellowing with veins still green (mottle)

• Leaves remain small and narrow with short stems.

• Most severe in spring growth.

skirting/pruning

Skirting: removing branches near the ground (skirt to 300mm above), watershoots and suckers

Pruning: removing branches that are dead + diseased, shaping the tree

3. Pest, diseases and deficiencies

Outline for a major disease; effect on pest/symptoms, management in a commercial setting

Collar Rot

Phytophthora citrophthora (occurs in poorly drained soil)

Effect:

• death of a section of bark on the trunk near ground level

• production of gum and splitting (as the bark dries)

Management:

• Treatment

  • Remove affected bark + paint with copper fungicide (also apply during autumn)

  • Phosphorous acid applied as a foliar spray

• Prevention

• Air: improve the air circulation near the trunk by keeping it clear of organic matter. 

• Moisture: Avoid wetting the trunk + improve soil drainage around the dripzone

• Avoid injuries to the lower trunk + ensure the bud union is well above soil level.

Outline for a major pest; lifecycle, appearance, effect on plant/symptoms, management in a commercial setting, prevention.

Major pests:

• Citrus leaf miner

• Aphids

• Fruit fly

• Bronze orange bug

Citrus leaf miner

Phyllocnistis citrella

Lifecycle:

• 1 generation: 14-17 days (favorable conditions)

• 6-10 days: eggs (0.3mm)

• Young larvae burrow underneath surface of leaf in mines

• 4 larval instars (stages)

  • 5-6 days: 3 stages (in summer)

  • 1 day: fourth instar (does not feed)

• Pupate for 6 days

• Moths lay eggs after 24 hours of mating

• Adult: less than a week - 20 days

Appearance:

• Adult:

  • 2.5mm long, 4.5 wingspan

• Light colored with brown and white markings

• black dot at the tip of forewing

• Larvae:

  • Pale green → yellowish brown

• Eggs: 

  • 0.3mm

  • Flat, ovalish

  • translucent

Effects/symptoms: 

• Eats leaf tissue (young leaves) - squiggly lines just beneath foliage surface

• Curls and twists leaves

• May affect growth on young trees

Management:

• managerial:

  • promote flush growth in spring by fertilizing in winter (pest absent)

  • limit flush growth in late summer and autumn (limit fertilizer + water)

• Biological: small parasitic wasps + lacewings

• Chemical: Insecticides (as a spray)

• Horticultural oil/white oil (female moths avoid laying eggs on leaves sprayed with oil) (used in JRAHS)

4. Sustainability

Explain and evaluate the impact of sustainable management by examining current practices in the James Ruse orchard.

Evaluate (4 marks)

• Outline (one sentence) (1)

• 2 Advantages (1)

• 2 Disadvantages (1)

• Judgement (one sentence, include a new/reworded adv and disadv) (1)

Current practices:

• Organic fertilizer

• Drip irrigation

• White oil

• Mulching

• (Kikuyu as a ground cover)

Organic fertilizer

Use of animal manure (Rooster Booster) to provide nutrients

Advantages:

• Provides nutrients NPK

• Adds organic matter (improves soil structure: more aeration and moisture retention)

• Environmentally friendly (reduces residues/pollution)

Disadvantages:

• Bulky

• Labor intensive

• Odor

• Not instantly available (2-2 months to break down and release nutrients)

The use of organic fertilizer is a sustainable practice, however, it is difficult to assess how much of the nutrients become available depending on the decomposition process.

Drip Irrigation:

Drip irrigation is a method which involves setting up a system of tubes and pipes which will deliver water one drop at a time. it is set up at the drip line of the tree, an imaginary line at the outer leaves of the tree, where the young roots soak up H2O really well. Orange trees require 39 to 49 inches of rainfall per year, at the Ruse farm, we get around 38 inches of rainfall per year, the drip irrigation is to make up for the difference.

Advantages:

• Conserves water by reducing evaporation and runoff

• Can be set up to deliver an exact volume of water in an exact amount of time

Disadvantages:

• Initial cost 

• Requires regular maintenance (plastic pipes become brittle)

• Gets blocked easily

• Suitable only for permanent crops/trees

Drip irrigation is a sustainable method of irrigation, however, it can only be used in permanent crops or trees.

White Oil

White oil is mineral/horticultural oil that is used to control insect pests.

Advantages:

• Natural product + environmentally friendly

• Does not leave any residue

• Doesn’t kill any non-target species (ladybirds, honeybees)

Disadvantages:

• Expensive (for large scale applications)

• Labor intensive (foliar spray)

• Reapplication every two weeks (oil breaks down in sunlight)

White oil is a sustainable practice, however, white oil should be avoided on very hot days as it burns the leaves.

Mulching

Mulching is the practice of spreading organic materials such as woodchips or straw around the base of the plant.

Advantages: 

• Reduction in weeds → reduction in labor. (weeds can’t get sunlight and stop growing)

• Retains moisture (so it does not evaporate quickly)

• Regulates soil temperature when it is too hot or too cold.

Disadvantages:

• Cost (of mulch)

• Labor intensive (spreading the mulching material)

• Bacteria takes energy from organic material for the process of decomposition.

Mulching is a sustainable practice because it reduces herbicide use.

Sample answer:

Animal manure, such as Rooster Booster, is used as an organic fertilizer on the JRAHS farm to provide nutrients. It provides the essential macronutrients nitrogen, phosphorus, and potassium, and adds organic matter, which improves soil structure and moisture retention. However, organic fertilizer can be bulky and thus labor intensive, and is not instantly available as it requires 2-3 months to break down and release nutrients. Overall, the use of organic fertilizer is a sustainable practice as it is environmentally friendly, but it is difficult to assess the quantity of nutrients that become available in the soil.

6. Post-harvest treatment

Waxing & Cleaning

Harvest:

• Weight: heavy for size

• Skin: Firm, finely textured

• Color: NOT an indicator of flavor or ripeness

Describe how technology is applied to oranges post-harvest and the treatment of oranges in preparation for marketing.

Describe: provide at least 3 details/pieces of information.

Technology

Mildura Fruit Company (MFC)

1. Integrated barcode scanning system: 

• Details ownership of the fruit throughout the whole process

• Record all packed products so marketing staff can sell

2. Touchscreen: 

• Entering defects/insects/harvest damage

• Segregating groups for specific markets

• Assessment report sent back to growers within 24h

3. Colorvision system technology: 

• sizes and grades

• Takes six images of each fruit as it rotates

• Up to 80 oranges per second

• Calculates volume and weight

• The company determines blemishes and colour/shape variations allowed in each class

4. Fruit label (using Sinclair labelling heads)

• Brand identification, PLU (price lookup detail)

5. Sunkist machine packers

• Suction

• Packing oranges

Treatment

Mildura fruit company

• Fungicide treatment (minimises risk of disease)

• Removal of unsound/decayed oranges

• Presizer (removes small oranges)

• High volume pressure wash (removes dirt)

• Fungicide treatment

• Wax application (seals the orange, reduces moisture and weight loss)

• Drying (gas-fired dying tunnels)

• Inspection + classing (through sorters)

• Sizing, grading

• Blemish sorter 

• Labelling with a sticker

Gillette citrus

• Washing/cleaning/fungicide

• Waxing

• Grading (separating oranges, both machine and hand-checked)

• Sizing (machine)

• Labelled with a sticker

In general:

• Washing

• Drying 

• Grading

• Blemishes, sizes, color

• Fungicide + waxing

• Packing 

Source: Mildura Fruit Compnay presentation video

1. Washing / Cleaning / Fungicide

• Washing: Oranges are dumped into a water flume or conveyor system where they are rinsed with clean water to remove dirt, dust, leaves, and field debris.
  
  
  
  
  

• Cleaning: Brushes and rollers scrub the oranges as they move through a machine. Water jets or spray nozzles may include a mild detergent or sanitizing solution.
  
  
  
  
  

• Fungicide application: A post-harvest fungicide (such as thiabendazole or imazalil) is applied during or after washing to prevent mold and decay during storage and shipping. This is often done by spraying or dipping.
  
  
  
  
  

• 
  

• 2. Waxing

• A thin layer of food-grade wax is applied after drying to replace the natural wax that may have been removed during washing.
  
  
  
  
  

• This wax improves the fruit’s appearance (glossy finish), reduces moisture loss, and extends shelf life.
  
  
  
  
  

• The waxing is done using sprayers or rollers, followed by soft brushes to ensure even coverage.
  
  
  
  
  

• 
  

• 3. Grading (Separating Oranges – Machine and Hand-Checked)

• Machine Grading: Oranges pass through high-speed cameras or optical sorters that scan each fruit for color, shape, surface blemishes, and defects.
  
  
  
  
  

• Manual Grading: Workers stationed along conveyors visually inspect the oranges to catch defects the machines might miss—like bruises, punctures, or skin diseases.
  
  
  
  
  

• Oranges that don’t meet quality standards are removed and sent for juice processing or discarded.
  
  
  
  
  

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• 4. Sizing (Machine)

• Oranges are mechanically sized using rollers or belts that sort the fruit by diameter or weight.
  
  
  
  
  

• Each size is typically associated with a specific count per carton (e.g., size 56 means 56 oranges per standard box).
  
  
  
  
  

• The sizing system ensures uniformity for packaging and marketing.
  
  
  
  
  

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• 5. Labeling (Sticker)

• Once graded and sized, oranges move along conveyors where a small machine applies adhesive stickers.
  
  
  
  
  

• The sticker includes information such as brand, PLU (Price Look-Up) code, and origin.
  
  
  
  
  

• This helps with retail tracking, consumer info, and inventory management.

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• 6. Packing (Loose or Bagged)

• Once the orange has gone through the steps above, it is then packed, either loosely in crates or in 4lb bags. In Australia, there is normally 3kg or 6.2lbs per bag.

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• 5. Marketing  

• Describe the markets the Washington Navel enterprise is trying to meet at James Ruse and in the wider industry.

• James ruse

• Ruse community

• Fresh fruit (no processing facility), $4 for 10-12 oranges

• 
  

• Wider industry:

• Mostly fresh fruit (60%)

• Export + domestic marketing

• Asia (China, Japan, Malaysia) - small fruit

• China: important factors = sweetness, rind/texture

• Orange export season in full swing (more info on exporting)

• 7. Interactions  

• Draw a systems diagram representing a citrus enterprise.

• Black box model

• Identifies basic inputs and outputs of a system at an enterprise level.

• Not concerned with the processes happening to transform inputs into outputs.

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• 
  

• Static systems model

• Includes the process

• May also indicate relationships between the process (order of events)

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• Dynamic agricultural systems

• Shows interactions between subsystems

• Indicates flow of material or information between parts of the system (subsystems)

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• Boundary: the JRAHS school/orchard fence

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• 
  Memorize the diagram above (this is the exact answer and WILL be in the yearly) (5 marks)

• Do NOT answer with a drawing of the orchard

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• Checklist:

• Boundary: Physical or financial limitation to the production system

• Inputs: Materials needed to produce the output

• Processes (+ subsystems, interactions)

• Output: Final products from production

• Monitoring: Gathering information in relation to the output

• Evaluation

• Feedback: The farm manager gathers information by monitoring the outputs so that a farm management decision can be made to improve production