Broccoli

Brassica oleracea

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Description

Broccoli, Brassica oleracea, is an herbaceous annual or biennial grown for its edible flower heads which are used as a vegetable. The broccoli plant has a thick green stalk, or stem, which gives rise to thick, leathery, oblong leaves which are gray-blue to green in color. The plant produces large branching green flower heads covered with numerous white or yellow flowers. Broccoli can be annual or biennial depending on the variety and can grow to 1 m (3.3 ft) in height. Broccoli may also be referred to as sprouting broccoli and likely originates from the Mediterranean although the exact location has not been determined.

Uses

Broccoli heads are consumed after boiling or fresh in salads. It can be processed for freezing and drying.

Propagation


Basic requirements
Broccoli is a cool season crop which can be grown both in spring and in fall. The plants thrive in cool climates and should be planted for fall in areas with hot summers. Broccoli grows best in moist, fertile soil with a slightly acidic pH between between 6.0 and 7.0 and at temperatures between 15.5 and 18°C (60–65°F). Broccoli has a high nitrogen requirement and due to the reduced activity of soil microbes in late fall and winter, organic matter should be added to the soil throughout the year to ensure an adequate supply of nutrients when broccoli is planted. In addition, broccoli requires regular water, especially during drought, to prevent the plants from going to seed. Plant broccoli in full sun to ensure optimum head size.

Sowing seeds
Broccoli can be direct seeded or started indoors for transplants. Spring plantings should be made 2–3 weeks before the last frost date in your area and Fall plantings should be made approximately 100 days before the first Fall frost. Sow seed 1.3 cm (0.5 in) deep in small groups of 2–3 seeds and about a week after emergence, thin to a final spacing of 30–60 cm (12–24 in) within the row, allowing 90 cm (36 in) between rows. Keep soil evenly moist after planting. If starting indoors, plant seed in peat pots to minimize disturbance to the roots when transplanting. Seedling can be planted outdoors when they are 3–4 weeks old at the same time as seeds are planted using the spacing detailed above. Plant transplants slightly deeper in the ground than they currently are in their pot and keep soil moist to ensure good fertility.

General care and maintenance
Broccoli has a very shallow root system and cultivating the soil around the plants to remove weeds should be avoided. Provide the plants with adequate and even moisture (about 2 in a week) to keep plants fertile and prevent them from bolting and avoid wetting the flower heads as they develop. Mulching around the plants helps to conserve soil moisture and reduces the soil temperature.

Harvesting
Broccoli is ready to harvest when the flower buds are firm and packed tightly in the head. Harvest before the buds open by cutting the stalk of the head at a 45° angle about 13–20 cm (5–8 in) below the head. Side-shoots will continue to produce after the first harvest.

Diseases

Alternaria leaf spot Fungus Alternaria brassicae

Symptoms

Small dark spots on leaves which turn brown to gray; lesions may be round or angular and may possess a purple-black margin; lesions may form concentric rings, become brittle and crack in center; dark brown elongated lesions may develop on stems and petioles

Comments

Disease emergence favored by warm, rainy weather

Management

Plant only pathogen-free seed; rotate crops; applications of appropriate fungicides control disease when present

Black leg Fungus Phoma lingam

Symptoms

Damping-off of seedlings; round or irregularly shaped gray necrotic lesions on leaves with dark margins; lesions may be covered in pink masses in favorable weather conditions

Comments

Favors warm, wet conditions; higher temperatures result in the development of more visible symptoms

Management

Use disease free seed or treat with hot water to remove fungus prior to planting; remove and destroy crop debris after harvest or plow deeply into soil

Black rot Bacteria Xanthomonas campestris

Symptoms

Irregularly shaped dull yellow areas along leaf margins which expand to leaf midrib and create a characterstic "V-shaped" lesion; lesions may coalesce along the leaf margin to give plant a scorched appearance

Comments

Pathogen is spread via infected seed or by splashing water and insect movement; disease emergence favored by warm and humid conditions

Management

Primary method of controlling black rot is through the use of good sanitation practices; rotate crops to non-cruciferous crops every 2 years; plant resistant varieties; control cruciferous weed species which may act as a reservoir for bacteria; plant pathogen-free seed

Clubroot Fungus Plasmodiophora brassicae

Symptoms

Slow growing, stunted plants; yellowish leaves which wilt during day and rejuvenate in part at night; swollen, distorted roots; extensive gall formation

Comments

Can be difficult to distinguish from nematode damage; fungus can survive in soil for periods in excess of 10 years; can be spread by movement of contaminated soil and irrigation water to uninfected areas

Management

Once the pathogen is present in the soil it can survive for many years, elimination of the pathogen is economically unfeasible; rotating crops generally does not provide effective control; plant only certified seed and avoid field grown transplants unless produced in a fumigated bed; applying lime to the soil can reduce fungus sporulation

Diamondback moth Insect Plutella xylostella

Symptoms

Young larvae feed between upper and lower leaf surface and may be visible when they emerge from small holes on the underside of the leaf; older larvae leave large, irregularly shaped shotholes on leaf undersides, may leave the upper surface intact; larvae may drop from the plant on silk threads if the leaf is disturbed; larvae are small (1 cm/0.3 in) and tapered at both ends; larvae have to prolegs at the rear end that are arranged in a distinctive V-shape

Comments

Larvae take between 10 and 14 days to mature and spin a loose, gauze-like cocoon on leaves or stems to pupate

Management

Larvae can be controlled organically by applications of Bacillus thurengiensis or Entrust; application of appropriate chemical insecticide is only necessary if larvae are damaging the growing tips of the plants

Downy mildew Fungus Hyaloperonospora parasitica

Symptoms

Small angular lesions on upper surface of leaves which enlarge into orange or yellow necrotic patches; white fluffy growth on undersides of leaves

Comments

Disease emergence favored by cool, moist conditions

Management

Remove all crop debris after harvest; rotate with non-brassicas; it is possible to control downy mildew with the application of an appropriate fungicide

Flea beetle (Crucifer flea beetle) Insect Phyllotreta cruciferae

Symptoms

Small holes or pits in leaves that give the foliage a characteristic “shothole” appearance; young plants and seedlings are particularly susceptible; plant growth may be reduced; if damage is severe the plant may be killed; the pest responsible for the damage is a small (1.5–3.0 mm) dark colored beetle which jumps when disturbed; the beetles are often shiny in appearance

Comments

Younger plants are more susceptible to flea beetle damage than older ones; older plants can tolerate infestation; flea beetles may overwinter on nearby weed species, in plant debris or in the soil; insects may go through a second or third generation in one year

Management

In areas where flea beetles are a problem, floating row covers may have to be used prior to the emergence of the beetles to provide a physical barrier to protect young plants; plant seeds early to allow establishment before the beetles become a problem - mature plants are less susceptible to damage; trap crops may provide a measure of control - cruciferous plants are best; application of a thick layer of mulch may help prevent beetles reaching surface; application on diamotecoeus earth or oils such as neem oil are effective control methods for organic growers; application of insecticides containing carbaryl, spinosad, bifenthrin and permethrin can provide adequate control of beetles for up to a week but will need reapplied

Large cabbage white (Cabbageworm) Insect Pieres rapae

Symptoms

Large ragged holes in leaves; green-brown frass (insect feces) on leaves; caterpillar is green in color and hairy, with a velvet-like appearance; may have faint yellow to orange stripes down back; slow-moving compared with other caterpillars

Comments

Butterfly larvae cause damage by feeding on plants; can be distinguished from other caterpillars by its sluggish movement; in large numbers larvae can cause extensive damage very quickly

Management

Hand pick caterpillars from plants and destroy; scrape eggs from leaves prior to hatching; apply appropriate insecticide if infestation is very heavy

Powdery mildew Fungus Erysiphe cruciferarum

Symptoms

Small white patches on upper and lower leaf surfaces which may also show purple blotching; patches coalesce to form a dense powdery layer which coats the leaves; leaves become chlorotic and drop from plant

Comments

Disease emergence favored by dry season, moderate temperatures, low humidity and low levels of rainfall

Management

Plant resistant varieties; rotate crops; remove all crop debris after harvest; remove weeds; avoid excessive application of nitrogen fertilizer which encourages powdery mildew growth; powdery mildew can be controled by application of sulfur sprays, dusts or vapors

Ring spot Fungus Mycosphaerella brassicicola

Symptoms

Small, purple spots surrounded by a ring of water-soaked tissue on leaves which mature to brown spots with olive green borders 1-2 cm across; spots may develop numerous fruiting bodies which give them a black appearance or develop a concentric pattern; heavily infected leaves may dry up and curl inwards

Comments

Ring spot requires cool, moist conditions to survive; disease symptoms typically develop in the fall and the peak of the infection occurs in winter

Management

Refrain from planting in areas known to have had disease previously; rotate crop to non-brassicas; sanitize tools and equipment regularly; apply appropriate fungicide if disease is identified in crop

Root knot nematode Nematode Meloidogyne spp.

Symptoms

Galls on roots which can be up to 3.3 cm (1 in) in diameter but are usually smaller; reduction in plant vigor; yellowing plants which wilt in hot weather

Comments

Galls can appear as quickly as a month prior to planting; nematodes prefer sandy soils and damage in areas of field or garden with this type of soil is most likely

Management

Plant resistant varieties if nematodes are known to be present in the soil ;check roots of plants mid-season or sooner if symptoms indicate nematodes; solarizing soil can reduce nematode populations in the soil and levels of inoculum of many other pathogens

Sclerotinia stem rot (White mold) Fungus Sclerotinia sclerotiorum

Symptoms

Irregular, necrotic gray lesions on leaves; white-gray leions on stems; reduced pod set; shattering seed pods

Comments

Disease emergence favors moderate to cool temperatures and high humidity

Management

Rotate crop to non-hosts (e.g. cereals) for at least 3 years; control weeds; avoid dense growth by planting in adequately spaced rows; apply appropriate foliar fungicides

Thrips (Western flower thrips, Onion thrips, etc.) Insect Frankliniella occidentalis
Thrips tabaci

Symptoms

If population is high leaves may be distorted; leaves are covered in coarse stippling and may appear silvery; leaves speckled with black feces; insect is small (1.5 mm) and slender and best viewed using a hand lens; adult thrips are pale yellow to light brown and the nymphs are smaller and lighter in color

Comments

Transmit viruses such as Tomato spotted wilt virus; once acquired, the insect retains the ability to transmit the virus for the remainder of its life

Management

Avoid planting next to onions, garlic or cereals where very large numbers of thrips can build up; use reflective mulches early in growing season to deter thrips; apply appropriate insecticide if thrips become problematic

White rust Fungus Albugo candida

Symptoms

White pustules on cotyledons, leaves, stems and/or flowers which coalesce to form large areas of infection; leaves may roll and thicken

Comments

Fungus can survive for long periods of time in dry conditions; disease spread by wind

Management

Rotate crops; plant only disease-free seed; apply appropriate fungicide if disease becomes a problem

Wirestem (Damping-off) Fungus Rhizoctonia solani

Symptoms

Death of seedlings after germination; brown-red or black rot girdling stem; seedling may remain upright but stem is constricted and twisted (wirestem)

Comments

Disease emergence in seedlings favored by cool temperatures

Management

Plant pathogen-free seed or transplants that have been produced in sterilized soil; apply fungicide to seed to kill off any fungi; shallow plant seeds or delay planting until soil warms

References

CABI Crop Protection Compendium. (2010). Brassica oleracea var. italica datasheet. Available at: http://www.cabi.org/cpc/datasheet/10094. [Accessed 07 November 14]. Paid subscription required.

Drost, D. & Johnson, M. (2010). Broccoli in the Garden. Utah State University Cooperative Extension. Available at: https://extension.usu.edu/files/publi.... [Accessed 07 November 14]. Free to access.

Hardin, N. C. (1996). Growing Broccoli. West Virginia University Cooperative Extension. Available at: http://www.wvu.edu/~exten/infores/pub.... [Accessed 07 November 14]. Free to access.

Rimmer, S. R., Shattuck, V. I. Buchwaldt, L. (Eds) (2007). Compendium of Brassica Diseases. American Phytopathological Society Press. Available at: http://www.apsnet.org/apsstore/shopap.... Available for purchase from APS Press.