Brussels sprouts

Description

Brussel sprouts, Brassica oleracea, are a cultivar of cabbage in the family Brassicaceae grown for their edible small leafy green buds, which resemble miniature cabbages. The plant has long, smooth and leathery leaves which can be green to purple in color and are arranged alternately on the stem. The sprouts form at the base of each leaf, in a long, spiral stem. The edible portion of the crop is the bud, which is a small cabbage-like head. It is a light green to green/blue in color. The plant is biennial but grown as an annual and can reach 0.6–1 m (2–3 ft) in height with a spread of 0.5–0.6 m (1.5–2 ft). Brussel sprouts may also be simply referred to as 'sprouts' and they originated from Northern Europe.


Uses

Brussel sprouts are most commonly eaten cooked as a vegetable. They may also be pickled in vinegar.


Propagation


Basic requirements
Brussels sprouts are a cool season crop which can be grown both in Spring and in Fall. The plants thrive in cool climates, maturing in cool or lightly frosty weather. In areas with hot summers, they should be planted for a Fall harvest. Brussels sprouts grow best in moist, fertile, well-draining soil with a slightly acidic pH between between 6.0 and 6.5 and at temperatures between 7 and 24°C (45–75°F), with optimum growth occurring at 15–18°C (59–64°F). Brussels sprouts have 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 sprouts are planted. Plant Brussels sprouts in an area that receives at least six hours of full sunlight for optimum growth and development.

Sowing seeds
Brussels sprouts 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 4 months 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 60 cm (24 in) within the row, allowing 76 cm (30 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
Brussels sprouts are sensitive to boron deficiency which can cause the plants to develop hollow stems and small buds. The deficiency can be corrected by adding boron to the soil. Brussels sprouts should be provided with adequate and even moisture (1.0 to 1.5 inches a week) to keep plants fertile and prevent them from bolting. Mulching around the plants helps to conserve soil moisture and reduces the soil temperature.

Harvesting
Brussels sprouts are generally ready for harvest 90 to 180 days after planting when the heads are firm and green and have reached between 2.5 and 5.0 cm (1–2 in) in diameter. The oldest sprouts are located at the bottom of the stalk and mature upwards. As sprouts are removed, it can be beneficial to remove the leaves which are beginning to yellow. Some people prefer to remove all of the leaves on the stalk to accelerate maturity and harvest in a manner similar to commercial sprout production. The stalks can be removed before the ground freezes over and stored indoors for further harvesting.


References

CABI Crop Protection Compendium. (2008). Brassica oleracea datasheet. Available at: http://www.cabi.org/cpc/datasheet/10102. [Accessed 07 November 14]. Paid subscription required.

Delahaut, K. A. & Newenhouse, A. C. (1997). Growing Broccoli, Cauliflower, Cabbage and other Cole crops in Wisconsin. A Guide for Fresh-Market Growers. University of Wisconsin Cooperative Extension. Available at: http://learningstore.uwex.edu/assets/.... [Accessed 07 November 14]. Free to access

Drost, D. & Johnson, M. (2010). Brussels Sprouts in the Garden. Utah State University Cooperative Extension. Available at: https://extension.usu.edu/files/publi.... [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.


Common Pests and Diseases

Black rot
Xanthomonas campestris

Symptoms
Seedlings develop wilted yellow to brown leaves and collapse; yellow, V-shaped lesions on mature leaf margins; dark rings can be found in the cross section of the stem
Cause
Bacteria
Comments
Can be confused with Fusarium wilt; favors warm wet environments
Management
Primary control methods based on good sanitation; plant disease-free seed; rotate crops every 2 years or less to non-brassica; avoid sprinkler irrigation

Downy mildew
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
Cause
Fungus
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 on brussel sprouts with the application of an appropriate fungicide

Powdery mildew
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
Cause
Fungus
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

White rust
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
Cause
Fungus
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

Fusarium wilt (Yellows)
Fusarium oxysporum

Symptoms
Dull yellow-green discoloration of leaves and stunted plant growth; lower leaves turning yellow-brown necrotic areas and dropping from plant; browning and defoliation spreading upwards from bottom of plant; symptoms more pronounced on one side of leaf than the other
Cause
Fungus
Comments
Fungus can survive for many years in soil and can enter plant through root tips or wounds; disease generally favors warm soil temperatures
Management
Plant resistant varieties; most other control methods are ineffective once disease has emerged; spread can be prevented by disinfecting equipment

Ring spot
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
Cause
Fungus
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

Alternaria leaf spot (Black spot, Gray spot)
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
Cause
Fungus
Comments
May become a problem during cool, wet periods
Management
Plant only pathogen-free seed; rotate crops; applications of appropriate fungicides control disease when present

Clubroot
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
Cause
Fungus
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

Sclerotinia stem rot (White mold)
Sclerotinia sclerotiorum

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

Cabbage aphid
Brevicoryne brassicae

Symptoms
Large populations can cause stunted growth or even plant death; insects visible on the plant leaves or sprouts and are small, grey-green in color and soft bodied and are covered with a white waxy coating; leaves may curl; insect excretes a sticky substance called honedew
Cause
Insect
Comments
Cabbage aphids feed only on cruciferous plants but may survive on related weed species
Management
If aphid population is limited to just a few leaves or shoots then the infestation can be pruned out to provide control; check transplants for aphids before planting; use tolerant varieties if available; reflective mulches such as silver colored plastic can deter aphids from feeding on plants; sturdy plants can be sprayed with a strong jet of water to knock aphids from leaves; insecticides are generally only required to treat aphids if the infestation is very high - plants generally tolerate low and medium level infestation; insecticidal soaps or oils such as neem or canola oil are usually the best method of control; always check the labels of the products for specific usage guidelines prior to us

Flea beetle
Systena blanda
Phyllotreta spp.

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
Cause
Insect
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)
Pieres rapae

Symptoms
Large ragged holes in leaves or bored into sprouts; 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
Cause
Insect
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

Diamondback moth
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, leaving 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
Cause
Insect
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

Cabbage looper
Trichoplusia ni

Symptoms
Large or small holes in leaves; damage often extensive; caterpillars are pale green with a white lines running down either side of their body; caterpillars are easily distinguished by the way they arch their body when moving; eggs are laid singly, usually on the lower leaf surface close to the leaf margin, and are white or pale green in color
Cause
Insect
Comments
Insects overwinter as pupae in crop debris in soil; adult insect id a dark colored moth; caterpillars have a wide host range
Management
Looper populations are usually held in check by natural enemies; if they do become problematic larvae can be hand-picked from the plants; an organically acceptable control method is the application of Bacillus thuringiensis which effectively kills younger larvae; chemical sprays may damage populations of natural enemies and should be selected carefully

Thrips (Western flower thrips, Onion thrips, etc)
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
Cause
Insect
Comments
Transmit viruses such as Tomato spotted wilt virus (see disease entry); 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

Root knot 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
Cause
Nematode
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