Insects, diseases and disorders of asian vegetables
Learn about symptoms, monitoring and potential management strategies for several common Asian vegetables.
Introduction
A wide range of new vegetable crops traditionally associated with Asian countries are grown in Ontario. These vegetable crops come from a range of plant families including cucurbits (related to cucumbers, squash, melons), crucifers (related to cabbage, broccoli, radish), legumes (related to peas, beans) and several others. Consult the OMAFRA Factsheet: Asian Vegetables Grown in Ontario, (Order No. 98-033), for further information.
Because of this wide range of plant families and their similarity to some vegetable crops already grown in Ontario many of the Asian vegetables suffer from the same insects, diseases and disorders as traditional crops. However, the symptoms, monitoring strategies and damage levels may vary depending upon the crop. In addition, several unique crops have unique insect, disease and/or disorder problems.
This Factsheet highlights symptoms, monitoring and potential management strategies for several common Asian vegetables. Refer to the following additional OMAFRA Factsheets and publications for more information that may be applicable to specific groups of Asian vegetables.
Table 1: Insects
| Insect | Crop(s) | Affected Symptoms | Monitoring | Management | References/ Figure(s) |
|---|---|---|---|---|---|
| Cabbage maggot (Delia radicum) | Nappa cabbage, bok choy, pak choy, choy sum, gai lan, yow choy, gai choy, lo bok (daikon) | larvae feed on rootswilting of young plants, followed by plant death tunnelling damage on radish bacterial soft rots often follow | monitor adult flies monitor egg laying activity monitor success of control measures i.e. damage levels | crop rotation field sanitation floating row covers biological control (rove beetles, predatory flies, etc.) preventative chemical treatments | 1, 2 |
| Flea beetles (Phyllotreta spp.) | As above | 'shot-hole' feeding damage on leaves | monitor 50-100 plants per field threshold is 1 flea beetle per plant | use transplants control cruciferous weeds floating row covers overhead irrigation registered insecticides | 3, 4 |
| Diamondback moth larvae, imported cabbageworm, cabbage looper (Plutella xylostella, Artogeia rapae, Trichoplusia ni) | As above | feeding holes in leaves frass (insect droppings) | monitor at least 25 plants in 5 groups of 5 twice weekly record % plants infested and predominate species | naturally occurring predators and parasites row covers Bacillus thuringiensis registered insecticides | Caterpillar Pests of Cruciferous Crops (Order No. 99-035) |
| Tarnished plant bug (Lygus lineolaris) | Nappa cabbage, bok choy, pak choy, gai lan, choy sum, hinn choy, tung choy, malabar spinach, bitter melon, fuzzy squash | tan to brown lesions on stems, petioles, leaves and flower stalks often followed by secondary bacterial soft rots | monitor 50-100 plants per field twice weekly record % plants infested or number of plant bugs per plant | field sanitation monitor nearby alfalfa fields control weeds biological control registered insecticides | Tarnished Plant Bug Damage on Vegetable Crops in Ontario (Order No. 98-025) |
| Cutworms (Noctuidae) | All crops | plants are cut off at ground level usually when small | monitor field for signs of damage dig in soil around plants with symptoms | naturally occurring predators and parasites weed control crop rotation registered insecticides | Managing Cutworms in Vegetable Crops (Order No. 00-055) |
| Leafminers (Liriomyza spp.) | Gai lan, yow choy, choy sum, bok choy, pak choy, chrysanthemum greens, malabar spinach, fuzzy squash, bitter melon | pin-head size punctures in leaves mining of leaves and petioles | monitor 50-100 plants for signs of damage record % plants infested sticky traps and sweep nets can be used to monitor adult flies | greenhouse sanitation crop rotation weed control biological control registered insecticides | Leafminers Attacking Greenhouse Crops (Order No. 14-037) |
| Aphids (Myzus persicae, Brevicoryne brassicae, Aphis gossypii) | All crops | aphid colonies curling, twisting of leaves and/or new growth stunted or poor growth | monitor 50-100 plants twice weekly record % plants infested and number of aphids per plant | biological control (syrphid, lacewing, ladybird larvae) heavy rainfall destroy crop residues avoid excessive nitrogen levels registered insecticides | 5, 6, 7 |
| Cucumber beetles (Acalymma vittatum, Diabrotica undecim-punctata) | Fuzzy squash, bitter melon, sweet melon, winter melon | feeding damage to leaves, stems, petioles and flowers beetle is a vector of the bacteria causing bacterial wilt disease | monitor 50-100 plants daily especially before the 5th leaf stage experimental threshold is 1-5 beetles per plant | row covers on small plantings prior to flowering registered insecticides | 8 |
| Squash bug (Anasa tristis) | As above | feeding damage on leaves, stems, petioles, flowers wilting plants | monitor 50-100 plants for adults, nymphs and egg masses record % plants infested and number of egg masses per plant experimental threshold is 1 egg mass per plant | crop rotation field sanitation registered insecticides | 9, 10 |
| Onion maggot (Delia antiqua) | Chinese chives | wilting plants secondary bacterial soft rots at base of plants | monitor adult flies with sticky traps monitor 100-1000 plants for damage | crop rotation field sanitation naturally occurring predators and parasites (rove beetles, predatory flies, etc.) row covers on small plantings | Onion Maggot Control (Order No. 00-017) |
| Seedcorn maggot (Delia platura) | Nappa cabbage, bok choy, fuzzy squash, bitter melon, winter melon | damage to seed and seedlings wilting plants feeding damage in mature Nappa or bok choy secondary bacterial soft rots | monitor 50-100 plants record % plants infested | row covers on small plantings seed treatment if available weed control minimize mechanical damage, herbicide burn, other damage to crop | N/A |
| Spider mites (Tetranychus urticae) (not an insect) | Fuzzy squash, bitter melon, winter melon, sweet melon, tung choy | speckling and bronzing of leaveswebbing between leaf petioles and stems | monitor 50-100 plants especially field border areas record % plants infested | biological control (predatory mites) | 11 |
Figure 1. Cabbage maggot larva
Figure 2. Damage to lo bok from cabbage maggot
Figure 3. Crucifer flea beetles
Figure 4. Shot hole damage from flea beetles
Figure 5. Green peach aphid.
Figure 6. Green peach aphid colony.
Figure 7. Cabbage aphid colony.
Figure 8. Striped cucumber beetle.
Figure 9. Adult squash bug
Figure 10. Squash bug egg mass.
Figure 11. Spider mites.
Table 2: Diseases
| Insect | Crop(s) | Affected Symptoms | Monitoring | Management | References/ Figure(s) |
|---|---|---|---|---|---|
| Clubroot (Plasmidiophora brassicae) | Nappa cabbage, bok choy, pak choy, yow choy, gai lan, choy sum, gai choy, lo bok (daikon) | plants wilting in patches during the day plants may be stunted swollen and disfigured roots | check areas with wilt symptoms conduct regular soil tests | adjust pH to 7.2 or higher avoid known infected areas improve drainage crucifer weed control reduce soil compaction long crop rotations | Fungal Disease of Cruciferous Crops (Order No. 85-043) and Integrated Pest Management for Crucifers (Pub. 701) |
| Downy mildew (Peronospora parasitica) | As above | pale yellow spots on upper leaf surface brown lesions and greyish mould on lower leaf surface | sample 50-100 plants and record % plants infested | avoid excess irrigation avoid planting too dense control crucifer weeds plow under crop residues after harvest | Fungal Disease of Cruciferous Crops (Order No. 85-043) and Integrated Pest Management for Crucifers (Pub. 701) |
| Alternaria leaf spot (Alternaria brassicae, Alternaria brassicicola) | As above | begins on older leaves as small yellow spots spots enlarge to dark brown with targetlike rings leaves often drop off and many black spores are observed | As above | As above and use hot-water treated seed | As above |
| Pseudo-cercosporella leaf spot (Pseudo-cercosporella capsellae) | Nappa cabbage, bok choy, pak choy | circular white to tan spots on leaves spots enlarge and become papery | As above | As above | Integrated Pest Management for Crucifers (Pub. 701) |
| Turnip mosaic virus (TuMV) | As above for clubroot | leaves may become mottled with yellow, light green patches plants may be stunted, twisted and distorted brown, sunken lesions found on stems and petioles | monitor aphid levels carefully monitor 50-100 plants and record % plants infested rogue out infested plants if numbers are low | control crucifer weeds and volunteer plants insecticide sprays are not effective in controlling the spread of TuMV | Integrated Pest Management for Crucifers (Pub. 701) |
| Soft rot (Erwinia carotovora & Pseudomonas spp.) | All crops | slimy, foul smelling watery rot often found at base of plant or near crown plants often collapse | monitor 50-100 plants and record % plants infested | control other insects and diseases reduce excess irrigation avoid excess nitrogen fertilization crop rotation especially with cereals do not plant too densely plow down diseased plants after harvest reduce mechanical damage to plants | Integrated Pest Management for Crucifers (Pub. 701) |
| Bitter melon, fuzzy squash, winter melon, sweet melon | starts as small white spots on leaves followed by spotting on stems later leaves may be covered with white, powdery fungal growth followed by yellowing and drop of leaves | monitor 50-100 plants and record % plants infested | use resistant varieties if available registered fungicides | 12 | |
| Bacterial wilt (Erwinia tracheiphila) | As above | wilting of the plants during the day, followed by yellowing and plant death when petioles are cut, sticky bacterial exudate may be observed | in early summer monitor activity of cucumber beetles which vector the disease monitor 50 -100 plants especially before the 5th leaf stage | apply labelled insecticides when threshold of 1.0-5.0 beetles per plant is reached rogue out infected plants | N/A |
| Snow peas | grey-brown, oval lesions on leaves circular, sunken, reddish-brown lesions on pods plants may be stunted and growing poorly | favoured by humid, wet weather monitor hot spots and generally check 50-100 plants and record % plants or % of crop affected. | crop rotation use disease-free seed reduce unnecessary irrigation | ||
| Other mosaic viruses (CuMV, TYMV, CaMV, BWYV, PVY) | As above for bacterial wilt | cucumber mosaic virus may affect Asian cucurbits turnip yellows mosaic, cauliflower mosaic, beet western yellows mosaic and potato virus Y may affect Asian crucifers mottled, wrinkled leaves, distortion of growth poor fruit set | monitor 50-100 plants and record % plants infested | use healthy certified seed rogue out infected plants monitor and control aphid vectors weed control | N/A |
Figure 12. Powdery mildew.
Figure 13. Anthracnose on snow pea
Table 3: Physiological Disorders
| Insect | Crop(s) | Affected Symptoms | Monitoring | Management | References/ Figure(s) |
|---|---|---|---|---|---|
| All crops | varies with crop and nutrient boron deficiency on lo bok characterized by internal browning of root magnesium and manganese deficiency characterized by interveinal yellowing, however Mn deficiency begins on the new leaves whereas Mg deficiency begins on older leaves nitrogen deficiency characterized by pale colour and poor growth | do a complete soil test monitor entire crop regularly foliar analyses for nutrients may provide useful management information | base fertilizer applications on complete soil test foliar nutrient sprays may help reduce symptoms of some deficiencies | 14, 15, 16 | |
| Tipburn | Nappa cabbage | edges of youngest leaves become brown secondary soft rots often follow | related to calcium nutrition and nutrient balance monitor as above | ensure that growth rate is consistent carefully manage irrigation and plant spacings | N/A |
| Oedema | Asian water spinach, some cucurbits and crucifers | raised bumps on leaves and/or fruit often occurs when soils are wet and warm and nighttime air is cool and saturated | monitor entire crop regularly | ensure water and temperature are consistent avoid excessive irrigation during periods when day-to-night temperatures vary greatly | N/A |
Click here for pictures. | All crops | varies with crop and herbicide poor or uneven germination poor growth stunted or distorted growth | As above | keep good records of field history monitor neighbouring crops also where appropriate | 17 |
| Cold injury | Cucurbits, water spinach, amaranth | poor growth, poor fruit set for water spinach, injury can occur below 12 degrees C | As above | floating row covers, plastic tunnels or houses will protect sensitive crops | N/A |
| Drought stress | All crops | poor growth, wilting, poor fruit set | As above | properly timed and judicious irrigation | N/A |
| Moisture stress | All crops | as above wilting, soft rots and stunting | As above | improving drainage reduce planting densities raised beds for some crops | N/A |
Figure 14. Boron deficiency in lo bok
Figure 15. Magnesium deficiency symptoms on radish
Figure 16. Nitrogen and/or phosphorous deficiency symptoms on gai lan
Figure 17. Trifluralin injury on yow choy (centre row)
Summary of the Tables
The above tables summarize the major insects, diseases and disorders encountered in Ontario Asian vegetables. However in some areas in certain growing seasons other problems may arise. As the acreage of these specialty vegetables increases, the same bacteria, fungi and viruses that cause problems on vegetables traditionally grown in Ontario may cause problems in Asian vegetables.
Although not observed in Ontario to date, some of the Asian crucifers (Nappa, bok choy, choy sum, gai lan, gai choy, etc.) may be susceptible to:
- bacterial leaf spot (Pseudomonas syringae),
- black rot (Xanthomonas campestris),
- damping-off (Pythium & Rhizoctonia species),
- Fusarium wilt (Fusarium oxysporum),
- earwigs (Forficula auricularia) and
- slugs (Deroceras spp.).
Although not observed in Ontario to date, some of the Asian cucurbits (fuzzy squash, bitter melon, winter melon, etc.) may be susceptible to:
- Anthracnose (Colletotrichum orbiculare),
- angular leaf spot (Pseudomonas syringae pv lachrymans),
- scab (Cladosporium cucumerinum),
- Fusarium rots (Fusarium spp.),
- gray mold (Botrytis cinerea),
- Alternaria leaf blights (Alternaria spp.),
- Ulocladium leaf spot (Ulocladium spp.),
- Pythium fruit rot (Pythium spp.),
- Phytophthora blight (Phytophthora capsici),
- Septoria leaf spot (Septoria cucurbitacearum),
- nematodes (Meloidogyne hapla & Pratylenchus penetrans) and
- squash vine borer (Melittia cucurbitae).
Growers of Asian water spinach (Tung choy) may also encounter grasshoppers, thrips and a number of fungal leaf blights due to Cercospora ipomoea or Phyllosticta ipomoea.
Growers of snow peas (ho lan dow) and snow pea shoots (dow miu) may also encounter bacterial blight (Pseudomonas syringae pv pisi), Ascochyta leaf and pod spot (Ascochyta pisi), seed decay, root rot or wilt (Rhizoctonia solani, Fusarium spp, Pythium spp.)
All of these pests are presently unusual and rarely cause significant losses.
Management of insects, diseases and disorders of Asian vegetables requires consistent and reliable field monitoring, as well as an understanding of all crop management component inter-relationships. This includes soil fertility and nutrition, keeping good records on rainfall, temperature and irrigation, variety selection, seed source and seed health, field selection, crop rotations, marketing requirements and post-harvest handling procedures.
Related Resources
- Aphids Infesting Lettuce & Celery in Ontario
- Caterpillar Pests of Cruciferous Crops
- Chinese Cabbage Production in Southern Ontario
- Fungal Diseases of Cruciferous Crops
- Leafminers Attacking Greenhouse Crops
- Managing Cutworms in Vegetable Crops
- Onion Maggot Control
- Pumpkin and Squash Production
- Tarnished Plant Bug Damage on Vegetable Crops in Ontario
Other OMAFRA Resources
- Integrated Pest Management for Crucifers, Publication 701 (Order this publication), with specific reference to some Asian crucifers.
- OMAFRA's Vegetable Crop Production Publications, with specific sections on specialty vegetables
- OMAFRA Vegetable web pages