Chinese cabbage
Description
Bok-choy (subspecies chinenesis)
Uses
Propagation
References
Common Pests and Diseases
Diseases
Category : Fungal
Alternaria leaf spot (Black spot, Gray spot) Alternaria brassicae
Alternaria lesions on Chinese cabbage leaf
Close-up of Alternaria lesions on chinese cabbage leaf
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 presentAnthracnose 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 fungusBlack rot 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
Cause
Bacterium
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 seedClubroot 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 economicall 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 sporulationDowny 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
Favors cool, humid weather; damage to the cabbage head may not be seen until the cabbage is cut open
Management
Remove all crop debris after harvest; rotate with non-brassicas; application of appropriate fungicides may be required if symptoms of disease are presentPowdery 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
isease 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 vaporsWatery soft rot (White mold, Cabbage drop) Sclerotinia sclerotiorum
Symptoms
Soft rotting area at base of stem which spreads upwards successively killing leaves by causing them to drop and infect the leaf below; when fungus reaches the head it causes a soft, slimy, watery rot
Cause
Fungus
Comments
Disease emergence is favored by frequent rainfall that keep soil close to saturation
Management
The number of sclerotia in the soil can be reduced by plowing crop debris deep into soil and rotating crops every 3 years with non-host crops; severe infestations may require control through application of appropriate fungicideWhite leaf spot Mycospaerella capsellae
Symptoms
Small, necrotic, brown spots on leaf tips or margins that matures to light gray or white with the original dark spot in center; margins of lesions may be darker; lesions may coalesce to form large chlorotic areas and cause defoliation
Cause
Fungus
Comments
Symptoms easily confused with downy mildew; disease emergence favored by wet leaves and cool temperatures
Management
No known plant resistance to white leaf spot so control relies on cultural practices such as rotating crops and removing weeds; application of appropriate fungicide may help control the diseaseCategory : Bacterial
Bacterial soft rot Erwinia caratovora
Symptoms
Water-soaked lesions on cabbage head which expand to form a large rotted mass of cream colored tissue which is liquid underneath; surface of lesions usually crack and exude slimy liquid which turns tan, dark brown or black on exposure to air
Cause
Bacterium
Comments
Bacteria are easily spread on tools and by irrigation water; disease emergence favored by warm, moist conditions
Management
Chemical treatments are not available for bacterial soft rot, control relies on cultural practices; rotate crops; plant cabbage in well-draining soils or raised beds; only harvest heads when they are dry; avoid damaging heads during harvestBlackleg Leptosphaeria maculans
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
Cause
Fungus
Comments
Favors warm, wet conditions; higher temperatures result in the development of more visible symptoms
Management
Cabbage does not have high levels of resistance to blackleg and fungicides use is uneconomical; 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 soilCategory :
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 useCabbage 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 useCategory : Fungal, Oomycete
Damping-off 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); in older cabbage plants sharply defined brown lesions appear on the underside of leaves; the lesions expand causing leaves to wilt and drop from plant
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 warmsPests
Category : Insects
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 larvaeCabbage 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
Cutworms
Agrotis spp.
Peridroma saucia
Nephelodes minians
and others
Cutworm feeding on plant stem
Cutworms will curl up into a characteristic C shape when disturbed
Cutworm larva severing plant stem
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 organicallyDiamondback 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 plantsLarge cabbage white (Cabbageworm) Pieres rapae
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
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
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 problematicCategory : Mites
Flea beetle 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