Brassica napus var. napus

Family: - Brassicaceae.


Brassica is the Latin name for cabbage.

Canola refers to low acid varieties of Brassica napus var. napus.

Other Names:

Oilseed Rape




Canola is an erect annual or biennial plant, normally 700 to 1500 mm tall with branching stems, yellow flowers in spring and globular black seed in a cylindrical pod. The basal leaves are usually blue-green, stalked, lobed, form a loose rosette and the lower leaves may be somewhat bristly. The stem leaves are smaller and usually not lobed. They have white to yellow (or occasionally pink to mauve) flowers with 4 petals each 11-14 long and 6 stamens. It flowers from late winter to spring mainly.

The seed pods that are slender, smooth, 45-100 mm long and almost cylindrical with several seeds. The narrower tip (beak) lacks seeds. Seed pods remain entire and do not break into smaller pieces.



Two. The kidney to heart shaped cotyledons are 5 to 8 mm long by 8 to 15 mm wide. Tip indented. Base tapering to squarish. Margins smooth. Hairless. Petiole 5 to 10 mm long, and hairless. The seedling has a long hypocotyl but no epicotyl.

First leaves:

The leaves grow singly, the first being 30 to 55 mm long with a petiole 5 to 15 mm long. They are oval and irregularly toothed rather than lobed like the later leaves. Tip pointed. Hairless or with some scattered hairs. Blue green.


The plant develops as a rosette that may exceed 500 mm in diameter

Stipules - None.

Petiole - Winged and broader toward the base

Blade - 100-300 mm long by 50-150 mm wide. Succulent, bluish green, often with a waxy bloom (glaucous), hairless or with short bristles on margins and veins on the under surface. The margin is lobed and from the second leaf on and these lobes are often completely separated towards the base of the leaf. The terminal lobe is usually the largest and has an rounded tip

Stem leaves - The lower stem leaves are similar to the later rosette leaves and are petiolate. The upper stem leaves are sessile and clasping, up to 100 mm long, smooth and hairless, and with a well defined lacy venation. The upper stem leaves and stems have a waxy bloom (glaucous).

Stem leaves:

Spear shaped. Clasping, no petiole.


The stems are polygonal in cross section, solid with a pithy core, and hairless. Up to 1500 mm tall. Many branched. Longitudinal striations are often present especially on later stems. They often have a purple tinge towards the base.

Flower head:

The inflorescence is a terminal raceme that matures from the bottom up and flowers are extended to be level with buds above. The stem (rachis) elongates with age.


On slender stalks.

The flowers are yellow and 6-25 mm in diameter.

Ovary -

Sepals -

Petals - four bright yellow petals, 8-15 mm long.

Stamens -

Anthers -


Pod, cylindrical, constricted between the seeds, 50-100 mm long by 5 mm wide, with a slender conical beak that is 10-12 mm long. Pods on short horizontal stalks to 30 mm long. Seeds in a single row.


Small, brownish black, spherical, 1 mm. Seed coat may have a fine, network pattern or be slightly pitted.


Thick taproot with .many laterals.

Key Characters:


Life cycle:

Annual or biennial. Usually, seeds germinate in autumn to winter and it forms a rosette in winter. In spring the flowering stem emerges and flowering occurs in late spring.

When germination occurs in late summer and early autumn the plants may flower before winter.

In summer rainfall regions, germination also occurs in spring and continues through the summer when there is sufficient moisture.


Time of flowering appears to be governed by the cultivar and the degree days since germination.


By seed. The flowers are pollinated by wind and insects. Honey bees have increased yield and oil production by about 20% when one hive per hectare is placed in crops. This is due to more but smaller seed being produced up to 200 m from the hive.(Rob Manning pers. comm.).

Flowering times:

Any time of year with a flush in spring and autumn.

Seed Biology and Germination:

Vegetative Propagules:

Some plants may over summer on their rootstock.


Brassica napus, Brassica rapa and Brassica oleracea freely interbreed and hybrids are common which can make identification difficult.


Population Dynamics and Dispersal:

Seed is mainly spread by human intervention.

Origin and History:


It may have originated from a hybrid between Brassica rapa and Brassica oleracea.





Cold or temperate.


Prefers well drained loamy soils.

Plant Associations:



Major crop for oil that is extracted from the seed.

Honey plant.



Weed of crops, vegetables disturbed areas and roadsides.


May accumulate toxic levels of nitrate.

May cause bloat, anaemia and pulmonary emphysema.

Volunteer canola may be toxic after spraying with herbicides in preparation for the following crop.

Toxicity from glucosinolates, isothiocyanates, SMCO and unknown compounds affects mainly cattle and rarely sheep or goats. Non ruminants are usually not affected but pigs have suffered abortion and other white skinned animals (including pigs) have suffered photo-sensitisation.


5 forms;
  1. Respiratory - shortness of breath and broken wind or grunting, especially if driven, and increased heart rate in cattle 7-10 days after grazing succulent canola.
  2. Digestive - 3 to 4 days after ingestion there is constipation, no bowel movement, small quantity of sticky black faeces, dark urine, loss of appetite, discomfort and may be jaundice in sheep and cattle.
  3. Nervous - Mania or depression, clouding of the eyes and degrees of blindness in sheep and cattle.
  4. Urinary - foaming red or dark urine, constipation anaemia, light mouth membranes, weakness, dejection, loss of appetite and may be jaundice in cattle and sheep.
  5. Photo-sensitisation in sheep, pigs and other white skinned animals.
  6. Nitrate toxicity.

Slowly introduce animals to green canola crops or sprayed areas. Don't graze frost affected, stressed or plants showing purple discolouration. Provide access to alternative feed.

Toxicity appears to be worse in dull weather, after rain or in stress conditions.

For Digestive form, give yeast, starches, gums, molasses an oily purgatives but not Epsom salts.

For Nervous form in cattle, give 500 mL molasses and 15-30 g sodium hyposulphite.


None. Seed imports should be screened for the presence of viruses.

Management and Control:


10 plants /m2 are usually worth controlling in cereal crops.

Eradication strategies:

These are not usually required.

Most of the Brassicaceae weeds have dormant seeds that continue to germinate throughout the season and for several years. They often mature and set seed very quickly. Manual removal is effective but must be done at least every 8-10 weeks. Once pods are formed, seed will often mature even if the plant has been uprooted. Soil disturbance often leads to a flush of seedlings.

Many are somewhat unpalatable, so grazing only offers partial control. They often flourish in undergrazed, sunny areas.

In bushland situations, fairly selective control can be achieved with 100 mL spray oil plus 0.1 g Eclipse® or 0.5 g Logran® in 10 L water. 5 mL Brodal® is often added to this mix to provide residual control of seedlings. Spray the plants until just wet from the seedling stage up to pod formation.

Isolated plants should be removed manually and burnt if flowering or seeding and a 10 m buffer area sprayed with 10 mL Brodal® in 10 L water.

500 mL/ha of glyphosate(450g/L) can be used at flowering to reduce the seed set of most species on roadsides without causing significant damage to most native plants.

Wick application with 1 part glyphosate(450g/L) in 2 parts water or overall spraying with 100 mL glyphosate(450g/L) in 10 L water provides reasonable control of most species though Wild Radish tends to regrow.

Herbicide resistance:

Triazine tolerant varieties have been bred.

Biological Control:

None likely to be developed because of it importance as a commercial crop.

Pests of canola include

Cabbage Aphid - grey and form dense clusters

Turnip Aphid - yellow to dark green with black legs

Green Peach Aphid - shiny green to yellow green

and occasionally Potato Aphid - pinkish green to light yellow.

False Wireworm

Vegetable Weevil

Related plants:

Black Mustard (Brassica nigra)

Broccoli (Brassica oleracea var. italica)

Brussels Sprouts (Brassica oleracea var. gemmifera)

Cabbage (Brassica oleracea var. capitata)

Cauliflower (Brassica oleracea var. botrytis)

Chinese Cabbage (Brassica chinensis)

Indian Mustard (Brassica juncea)

Kale (Brassica oleracea var. acephala)

Kohlrabi (Brassica oleracea var. gongylodes)

Mediterranean Turnip (Brassica tournefortii)

Rapeseed (Brassica rapa var. sylvestris)

Savoy cabbage (Brassica oleracea var. sabauda)

Smooth Stemmed Turnip (Brassica oxyrrhina)

Swede (Brassica napus var. napobrassica)

Turnip (Brassica rapa var. rapa)

Twiggy Turnip (Brassica fruticulosa)

Winter Rape (Brassica napus var.biennis)

Brassica elongata

The native Brassicaceae species usually have short, broad and smooth pods.

Plants of similar appearance:


Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P181.

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P210-212

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #195.7.

McBarron, E.J. (1983). Poisonous plants. (Inkata Press, Melbourne). P92-93. Diagram.

Moerkerk, M.R. and Barnett, A.G. (1998). More Crop Weeds. R.G. and F.J. Richardson, Melbourne. P64. Diagrams. Photos.


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