Kale

Description

Kale, Brassica oleracea variant acephala, is a leafy herbaceous biennial or perennial plant in the family Brassicaeae grown as a leafy green vegetable. The kale plant is a non-heading, cabbage like plant with curly or straight, loose blue-green or purple leaves. Kale is usually grown as as an annual plant, harvested after one growing season and can reach a height of 1 m (3.3 ft). Kale may also be referred to as borecole or non-heading cabbage or broccoli and its exact origins are unknown, although it grows native in regions of the eastern Mediterranean and Asia.


Uses

Kale is used as a green vegetable and is usually cooked before consumption. Some varieties of kale are grown as decorative ornamental plants due to their attractive, brightly colored foliage.


Propagation


Requirements
Kale is cool season crop that grows best in cool, moist conditions. The plant will grow best at temperatures between 4 and 21°C (40–50°F) allowing it to be grown in both Spring and Fall. Kale is a hardy plant, tolerating frost, and will grow optimally in a rich, moist, well draining soil with a pH of 6.5. Kale requires at least six hours of direct sunlight every day.

Sowing seeds
Kale can be direct seeded or started indoors for transplants. The optimum soil temperature for germination is between 12 and 24°C (55–75°F). Kale seeds should be planted after any danger of hard frost or in a cold frame for transplanting to their final location. For a Fall harvest, try to time seeding so that the plants will mature in cool weather. This often means sowing in July but may be as late as October in warmer Southern regions. Prepare the soil for planting through the addition of nitrogen in the form of bone meal or composted manure. Plant seeds 12 mm (0.5 in) deep allowing 3.5 cm (1 in) between plants in the row. Thin seedlings to a final within row spacing of 45–60 cm (18–24 in). Keep soil moist during germination to prevent a crust from forming on the soil surface as this will cause uneven germination.

Transplanting
Seedlings started indoors or in a cold frame are ready to be transplanted when they have 3–4 leaves and the daytime temperature has reached 10°C (50°F). Seedlings should be planted at the final spacing for seeds (45–60 cm/18–24 in between plants and 0.6 to 1.2 m/2–4 ft between rows). Plant each seedling slightly deeper than it was previously. The plantings can be staggered in 2 week intervals to prolong the harvest.

General care
Kale should be kept evenly watered, application of mulch around plants helps to conserve soil moisture. The plants have shallow roots and in order to avoid damaging them, it is preferable to hand pull any weeds growing around the plants. Kale plants are heavy feeders, requiring plentiful nitrogen to meet their growth requirements and develop optimally. Apply an appropriate complete fertilizer when thinning seedlings.

Harvesting
Kale leaves can be harvested when they are 20–25 cm (8–10 in) long. Harvest the outer leaves to avoid damaging the growing tip of the plant. Kale leaves are sweeter when they are harvested after frost.


References

Anderson, C. R. Home Gardening Series. Kale. University of Arkansas Division of Agriculture. Available at: http://www.uaex.edu/publications/pdf/.... [Accessed 21 December 14]. Free to access.

Drost, D. & Johnson, M. (2005). Kale in the Garden. Utah State University Extension. Available at: http://extension.usu.edu/boxelder/fil.... [Accessed 21 December 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 (Leaf spot)
Xanthomonas campestris

Symptoms
V-shaped brown lesions originating from edge of leaves; black leaf stems and drop from the plant; black discoloration of stem; brown spots on leaves.
Cause
Bacteria
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.

Alternaria leaf spot (Black spot, Gray spot)
Alternaria brassicae
Alternaria brassicicola

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 on cabbage during cool, wet periods.
Management
Plant only pathogen-free seed; rotate crops; applications of appropriate fungicides control disease when present.

Anthracnose
Colletotrichum higginsianum

Symptoms
Small circular or irregularly shaped dry spots which are gray to straw in color on leaves; a high number of spots may cause the leaf to die; lesions may coalesce to form large necrotic patches causing leaves to turn yellow and wilt; lesions may split or crack in dry centers
Cause
Fungus
Comments
Fungus overwinters on leaf debris and on related weeds; disease emergence is favored by moist, warm conditions
Management
Control of disease depends on sanitary practices; treat seeds with hot water prior to planting; rotate crops; plant in an area with good soil drainage; remove all cruciferous weeds which may act as a reservoir for the fungus

Damping-off (Wirestem)
Rhizoctonia solani

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

Downy mildew
Peronospora parasitica

Symptoms
Irregular yellow patches on leaves which turn light brown in color; fluffy gray growth on the undersides of the leaves.
Cause
Fungus
Comments
Disease emergence favored by cool, moist conditions.
Management
Remove all crop debris after harvest; rotate with non-brassicas; application of appropriate fungicides may be required if symptoms of disease are present.

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 and should be selected carefully.

Beet armyworm
Spodoptera exigua

Symptoms
Singular, or closely grouped circular to irregularly shaped holes in foliage; heavy feeding by young larvae leads to skeletonized leaves; shallow, dry wounds on fruit; egg clusters of 50-150 eggs may be present on the leaves; egg clusters are covered in a whitish scale which gives the cluster a cottony or fuzzy appearance; young larvae are pale green to yellow in color while older larvae are generally darker green with a dark and light line running along the side of their body and a pink or yellow underside.
Cause
Insect
Comments
Insect can go through 3–5 generations a year.
Management
Organic methods of controlling the beet armyworm include biological control by natural enemies which parasitize the larvae and the application of Bacillus thuringiensis; there are chemicals available for commercial control but many that are available for the home garden do not provide adequate control of the larvae.

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; 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.

Cabbage aphid
Brevicoryne brassicaea

Symptoms
Large populations can cause stunted growth or even plant death; insects may be visible on the plant leaves and are small, grey-green in color and soft bodied and are covered with a white waxy coating; prefer to feed deep down in cabbage head and may be obscured by the leaves.
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 use.

Large cabbage white (and Cross-Striped Cabbageworm)
Pieres rapae
Evergestis rimosalis

Symptoms
Large ragged holes in leaves or bored into head; 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
Larvae can be distinguished from other caterpillars by their 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, 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.
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.

Cutworms
Agrotis spp.
Peridroma saucia
Nephelodes minians
and others

Symptoms
Stems of young transplants or seedlings may be severed at soil line; if infection occurs later, irregular holes are eaten into the surface of fruits; larvae causing the damage are usually active at night and hide during the day in the soil at the base of the plants or in plant debris of toppled plant; larvae are 2.5–5.0 cm (1–2 in) in length; larvae may exhibit a variety of patterns and coloration but will usually curl up into a C-shape when disturbed.
Cause
Insects
Comments
Cutworms have a wide host range and attack vegetables including asparagus, bean, cabbage and other crucifers, carrot, celery, corn, lettuce, pea, pepper, potato and tomato.
Management
Remove all plant residue from soil after harvest or at least two weeks before planting, this is especially important if the previous crop was another host such as alfalfa, beans or a leguminous cover crop; plastic or foil collars fitted around plant stems to cover the bottom 3 inches above the soil line and extending a couple of inches into the soil can prevent larvae severing plants; hand-pick larvae after dark; spread diatomaceous earth around the base of the plants (this creates a sharp barrier that will cut the insects if they try and crawl over it); apply appropriate insecticides to infested areas of garden or field if not growing organically.

Flea beetles
Phylotreta 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
Insects
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.

Root-knot nematode
Meloidogyne spp

Symptoms
Areas of irregular growth on plant; stunted plant growth; plants wilt during hot afternoons during periods of water-stress; galls on roots
Cause
Nematode
Comments
Root-knot nemtodes are easily spread via movement of infected soil; root-knot nematodes have a wide host range which includes many weed species which can act as reservoirs for infection
Management
Rotate crops every 1-2 years to non-host; avoid transferring soil from infested fields; soil fumigation with nematacide or application of non-fumigant nematicide may be required to manage heavy infestations