Broccoli is a member of Cruciferae, the cabbage family. Its botanical name is Brassica oleracea cv.italica, the same as cauliflower. Broccoli is similar to cauliflower in its upright structure, leaf habit and head formation. Consumption and production has increased significantly over recent years and has gone from 7 700 tonnes in 1989/90 to 16 600 tonnes in 1992/93.
Broccoli is easer to grow and can withstand a wider range of conditions than cauliflower. It is cultivated in a similar way to cabbages. Broccoli is grown year round in Victoria but the period of highest quality varies depending on the production area.
World wide, broccoli has created new interest as a vegetable. For example, in Australia product quality has improved out of sight and the result is a growing demand for broccoli on the domestic and export markets. There are three main reasons for this; new large central-heading varieties, modern marketing methods and consumer acceptance.
Sound markets are built upon having a product of consistent quality and supply. Without the large central heading varieties and closer plant spacings in the field, it would be impossible to achieve the volumes expected in today's market place. Markets now demand broccoli heads around 300 to 400 grams each; consumers can clearly see the quality and volume of each head they are buying.
Another factor to influence markets is in the overall head shape and colour for different broccoli varieties; (this is discussed again in more detail). Export and processing markets in particular can be very strict in their preference for shape, bud formation, colour, spear length and weight.
To ensure the market is supplied with the product quality it expects, careful attention must be given to all areas that influence production, harvesting, post harvest handling and marketing.
Victorian grown broccoli can be found on the Melbourne market for twelve months of the year. Broccoli can be grown in all parts of Victoria, but it adapts better to the milder conditions found in most southern parts of the State. The supply period of high quality broccoli is larger in southern areas of the State.
Broccoli crops growing in very sheltered areas are more likely to be affected by head rot, a disease of the broccoli head.
Broccoli can be grown on a wide range of soil types, from light sandy loams through to heavy clay loams. However, the soil must be well drained, regardless of type. Drainage may have to be improved by raising beds, draining or scooping headlands to remove surplus water, and laying of underground pipe drains.
The soil acidity should be somewhere between pH 6.0 and 6.5. If it is less than pH 6.0, apply lime at least six weeks before planting. Do not over-lime.
There is a wide range of cultivars available and these are constantly changing. Virtually all commercial types are hybrids. Two of the most common varieties currently grown are Marathon and Greenbelt.
Suitable hybrids sown in their best time slots mature very evenly. Each cultivar therefore needs to be checked carefully over a range of sowing and planting times, against local conditions.
If direct drilling is to be used, pay extra attention to preparing the soil for germination of seed and to control weeds. Direct seeding saves labour, but a direct-seeded crop does occupy the ground for about five or six weeks longer than a transplanted crop.
If the processor or market wants a smaller head of broccoli, direct seeding with a precision seeder is one way to achieve this.
Simply closing up the in-row spacing increases the number of plants per hectare. The closer spacing of the plants reduces the size of heads through increased competition, but may not increase market yield with all varieties in a once-over harvest.
One kilogram of broccoli seed could contain about 180,000 seeds, that is, about 180 seeds per gram; quantities will vary between varieties. Use table 1 as a guide where the in-row plant is 200 mm.
Table 1. A guide to seed quantities
Distance between rows (mm) Number of plants per ha Amount of seed per ha (g)
1 050 83 333
47 619 460
Note: For in-row spacing of 400 mm, simply halve the listed weight of seed.
The amount of seed needed can vary because of the germination percentage of the seed, the condition of the seed bed at time of sowing, the spacing of the plants in the field, or the type of drill used. Precision seed drills use less seed but cost much more than other machines.
Commercially, most seedlings are now produced by nurseries using cell trays.
To produce bare rooted seedlings, a seed bed of 100 grams of broccoli seed will produce about 16 000 to 18 000 good seedlings; therefore between 200 g and 300 g of seed sown in rows over 80 to 100 sq m should provide enough plants for one hectare. The number of plants needed will depend on field spacing.
Buy seedlings from nurseries that practise steam sterilisation of the soil mixtures and seeding trays. Insist on hot-water treatment of all seed to control seed-borne diseases.
Seedlings produced in cubed or cell trays or small peat pots do have advantages but such seedlings will cost more. However, this method does save time and seed and the transplant check to the seedling is minimal, with a more even crop produced.
The better the preparation of the soil, the better the strike at transplanting; the weed problem is also greatly reduced. Seedlings are usually transplanted using a transplant machine.
Once the seedlings have been transplanted, they should be irrigated and kept growing steadily, as any check is likely to produce premature heading. Control weeds and carefully irrigate the crop if necessary.
These are usually from 200 mm to 300 mm within the row. Between-row spacing depends on local cultural methods and tractor widths. For example, a tractor width of l.5 m and 1.8 m would have at least two to three rows between the wheels.
Manures and fertilisers
Selection of a fertiliser program depends upon the phosphorus and potassium levels in the soil. These are best determined from reliable soil sampling and soil analysis programs which should be carried out well before planting.
As a general guide any of the following fertiliser may be used; the choice depends upon the soil type, previous cropping history and the soil analysis result:
NPK 5:6:2 900 to 1600 kg/ha
NPK 6:6:6 900 to 1600 kg/ha
NPK 5:8:4 700 to 1200 kg/ha
NPK 8:1:10 525 to 900 kg/ha
If fowl manure (deep litter) is available and is applied at a rate of 22 cu m per ha, the fertiliser rates can be reduced by one-third. The phosphorus and potassium level can only be lowered by using N: P: K 5:6:2 at the rate of from 800 kg to 1200 kg per ha.
In most soils and locations, crops need added nitrogen and potassium during their growing and maturing times. These can be applied as solid side-dressings, or in the case of urea and potassium nitrate, as a foliar spray.
Solid side dressings:
NPK 20:0:10 200 to 300 kg/ha
NPK 20:0:16 200 to 300 kg/ha
NPK 16:0:0 250 to 375 kg/ha
NPK 21:0:0 200 to 275 kg/ha
NPK 34:0:0 125 to 175 kg/ha
NPK 46:0:0 85 to 125 kg/ha
On coarse soils, a light side-dressing is often needed four to six weeks after transplanting. The main side-dressing is applied at the earliest sign of the flower appearing.
At least one solid side-dressing may be replaced by a foliar spray of urea and potassium nitrate. The wetting agent Agral 60 must be used at the rate recommended on the label.
Farmers should be aware of the potential dangers of using phosphatic fertilisers with high levels of cadmium. Research has shown that the use of phosphatic fertilisers which contain the heavy metal cadmium as a contaminant can increase cadmium levels in both soil and potatoes.
There are legal maximum levels of cadmium allowable for vegetables sold in Australia, however no violations have been recorded for broccoli as a result of survey investigations. Fertilisers containing cadmium in excess of 1 mg/kg are required to state the following warning.
"WARNING––this product contains cadmium. Continued use of this product in agricultural situations may lead to residue levels in plant and animal products in excess of the maximum level specified by the Australia New Zealand Food Standards Code and the accumulation of cadmium in soils."
It is in the grower's and consumer's interest to minimise the addition of cadmium to soils and agricultural produce. Growers should consult fertiliser suppliers or manufacturers for advice on the cadmium levels of fertilisers they are considering using. There are a number of low cadmium horticultural fertilisers marketed today. These have lower levels of cadmium than some superphosphate and other fertilisers.
Common nutrient deficiencies
Molybdenum deficiency (whiptail)
The symptom of molybdenum deficiency is malformed, thick and leathery leaves. The plants show a general lack of vigour. To prevent this deficiency, or to treat affected plants, apply a foliar spray of molybdenum as ammonium or sodium molybdate.
The condition is often induced by acid soil, so check the pH of the soil. Lime will be needed if the pH is less than 6.0.
Note: Where cropping soils with a history of molybdenum deficiency are being alternated with grazing, expert advice must be obtained as to the use of molybdenum on soil that will grow pasture.
Excessive applications of lime may cause a deficiency of manganese. The main symptom of the disorder is a severe leaf mottling between the veins, which regain their normal colour. At maturity, the deficiency may induce breakdown spots in the central head. The condition can be corrected by a foliar spray of manganese sulphate. Several applications may be needed, depending on the severity of the deficiency.
Deficiency symptoms generally occur in the younger, growing parts of the plant. Water-soaked areas appear in the centres of the small branches of the head, and leaves around the head may be deformed. At harvest, the stem is hollow.
Dry soil conditions increase the problem. A foliar spray of 0. 1% boron (1 kg in 1000 L of water) will correct the condition. Don't apply too much because vegetables generally are very sensitive to boron and the range between the amount required and the amount which is toxic is very narrow.
Note: Use a wetting agent such as "Agral 60" to gain the greatest benefit from foliar-applied nutrients. However, do not apply foliar sprays once the central head emerges because it is very sensitive and is easily damaged by most chemicals.
Potassium deficiency (leaf scorch or marginal leaf burn)
Apply a side-dressing of muriate of potash at from 200 kg to 300 kg per hectare to correct the deficiency.
The most destructive and damaging insects are aphids and the caterpillars of the cabbage white butterfly and the diamond-back cabbage moth. For control of diamond back moth it is important to vary the chemical application program with different chemical groups to reduce the potential for resistance to develop. There is a resistance management strategy for diamond back moth and for more information contact us.
Heliothis caterpillars can be a problem at times, particularly on a paddock straight out of pasture.
There are many chemicals registered to control these pests.
The APVMA maintains a database of all chemicals registered for the control of pests in Australia. Refer to theAPVMA website or your chemical reseller for chemicals registered for the control of pests. Ensure you meet the relevant Maximum Residue Limits (MRLs) for the chemical in the end market, be it domestic or export.
Chemical users must ensure they read and understand all sections of the chemical label prior to use.
Fungal diseases of broccoli include Alternaria, blackleg, clubroot, downy mildew, ringspot, light-leaf spot andsclerotinia sp. Also damping-off problems can be caused by Pythium, Rhizoctonia and Fusarium sp.
Bacterial diseases include blackrot, broccoli headrot and head-stem rot.
Two viral diseases, cauliflower mosaic and turnip mosaic also can infect broccoli and cause production losses.
Control of disease starts with the seed which should be heat treated by immersing in water at 50°C for 20 minutes. This will control diseases carried on the seed such as blackleg, blackrot and a range of leaf spot diseases.
Seedbed seedlings should be produced only in soil that has not been used for field cropping. The seed bed area must be treated and managed in a manner that controls soil-borne diseases or prevent their introduction.
A rigid disease control program is needed for growing mixes and plants in cell-trays.
Chemical weed control
Chemical weed control, when understood and used with time accuracy, is a great cost-saving tool. There are three basic methods of chemical weed control in broccoli:
• Incorporation of herbicide into the soil before direct seeding or transplanting;
• Application immediately after seeding (pre-emergence to crop);
• Application after crop emergence or after transplanting of the seedlings (post emergence to the crop).
It is important to understand and follow the label directions when using a herbicide in order to avoid damaging your broccoli.
Note: There are no knockdown herbicides currently registered for use on broccoli to control broadleaf weeds growing in the crop. There are herbicides available for control of grass weeds within a crop.
For the registration status of these products, please refer to Australian Pesticides and Veterinary Medicines Authority, your chemical reseller or your local chemical standards officer. Ensure you meet the relevant Maximum Residue Limits (MRLs) for the chemical in the end market, be it domestic or export.
Chemical users must ensure they read and understand all sections of the chemical label prior to use.
Harvesting and marketing
Start harvesting before the central head begins to loosen, that is, while the head is still tight and before there is any sign of yellowing in the buds. Harvesting may continue for several weeks with several cuts carried out per crop. Use a clean knife to harvest the spears with a straight cut leaving about 150 mm of the stalk below the head. Stem length may vary depending on market requirements.
Broccoli harvested into bulk bins in the field is a practical method, but throwing or dropping will cause damage and loss of quality. The time from harvest to cool room must be less than two hours to prevent loss of quality.
The core temperature of broccoli should be reduced four degrees C. as quickly as possible. For export broccoli the temperature should then be lowered to one to two degrees C. and held at this point for at least 24 hours. Marketing broccoli in cartons by weight is now the accepted method. The net weight of broccoli should be seven or eight kg plus two to three kg of flaked ice; the carton is used with a plastic liner bag.
Sometimes there is a marketing opportunity for broccoli in bulk bins. A plastic liner and ice are used in the same way as with cartons.
The market requires mature heads of uniform size and weight. Stem length and diameter of the head will be dictated by the market; generally in the range of 100 to 150 mm for each. Variety and season will affect market specifications to some degree.
Side shoots: The Market interest for side shoots has declined in recent times. Side shoots begin to develop once the central head has been removed. Not all varieties are suited to side shoot production.
Picking of side shoots begins when they are about 50 to 80 mm across, are tied into bunches weighing about one kg and sold in units of ten bunches or one dec. Sometimes there is a market demand for a loose-fill into plastic lined cartons with ice.
The weight and name of the contents, together with the name and address of the grower, must appear on the outside of the container.
Recommendations for post-harvest handling of broccoli for sea freight
Considerations before start
(i) Refer containers operate on 3-phase power so a suitable outlet and extension cord must be available at the packing shed.
(ii) If the container is to be off-power for an extended period during transportation from the packing shed to the wharf, a portable 3-phase generator is needed to maintain power to prevent excessive warming.
Broccoli heads must be of good quality to start with. They should be firm and green with an even bead size Heads with "cat's eyes", or that are loose or "blown" should not be included. Heads must be free from soil and insects and uniform in size.
Heads should be precooled to as close to 0°C as possible within 1 to 2 hours of harvest. After pre-cooling they should be stored at 0°C and 95 to 100% RH.
Packing and packaging
Packing should be done rapidly in a cool place and the packed product returned immediately to the cool room. Heads should not be allowed to warm up to more than 2° to 3° during packing. Packages should be strong and prevent moisture loss. A fully waxed fibreboard carton (Australian tray carton) with a low density polyethylene liner is suitable. Usually 8 or 9 kg of broccoli is packed in each carton. Do not use ice or polystyrene boxes for sea freight. Modified Atmosphere Packaging (MAP) is a recent technological development that uses a gas permeable plastic film to maintain quality of broccoli over an extended storage life. For more information on the use of MAP contact us.
The temperature of the broccoli when the container is stowed must be less than 2°C. Cartons should be column-stacked to give maximum compressive strength and air movement, with dunnage (32 ´ 10 mm battens) between packages every second row. In a conventional 6 m, integral-refrigeration unit shipping container there will be 10 rows or seven cartons, seven high (10 ´ 7 ´ 7) plus one cross row of 4 cartons 7 high (7 ´ 4) to give a maximum stow of 518 cartons.
The container should be on power and operating at least 1 hour before stowing. The supply air temperature should be set at -0.5°C with minimum ventilation, usually 15 3 metres per hour.
Recommendations for post harvest handling of broccoli for air freight
Essentially they are the same to those for sea freight in the sections for quality; precooling; sorting and grading; and, packing and packaging. There are some further guides.
Packing and packaging
The polystyrene lidded box and waxed cartons are used for air freight broccoli with 3 kg of added ice. Cartons are only used in our winter months for short journeys no further than Singapore and then only by agreement with the importer.
Once the container leaves the packing shed it may not be stored again under refrigeration before arriving at an overseas market. It is in the interest of the seller and the buyer, that all aspects of temperature and quality control described under sea freight, are strictly followed. The 3 kg of ice should only be added after the core temperature of broccoli has been stabilised to between 0 - 1 °C.
It is never easy to estimate yield because of the possible multiple harvests. In the case of broccoli, if the central head only is taken into account, the yield can range from 5 to 7.5 tonnes/ha. This is based on a spacing of 900 mm by 300 mm.
Broccoli deteriorates very quickly once harvested, so cool it as soon as possible. Otherwise, harvest early in the morning and move the broccoli quickly from the field into a cool shelter to help them retain their low night temperature.