Insects, Diseases and Disorders of Asian Vegetables


Factsheet - ISSN 1198-712X   -   Copyright Queen's Printer for Ontario
Agdex#: 259/605
Publication Date: 11/00
Order#: 00-095
Last Reviewed: 01/13
History: Original Factsheet
Written by: Jim Chaput - former Vegetable IPM Specialist/OMAFRA; Dr. Ray Cerkauskas - Research Scientist/ AAFC

Table of Contents

  1. Introduction
  2. Table 1: Insects
  3. Table 2: Diseases
  4. Table 3: Physiological Disorders
  5. Summary of the Tables
  6. Related Factsheets
  7. Other OMAFRA Products

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 roots

 

•wilting 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
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
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
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
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
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

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

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

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
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 leaves
  • webbing between leaf petioles and stems
  • monitor 50-100 plants especially field border areas
  • record % plants infested
biological control (predatory mites)

 

Cabbage maggot larva

Figure 1. Cabbage maggot larva

 

Figure 2. Damage to lo bok from cabbage maggot

Figure 2. Damage to lo bok from cabbage maggot

 

Figure 3. Crucifer flea beetles

Figure 3. Crucifer flea beetles

 

Figure 4. Shot hole damage from flea beetles

Figure 4. Shot hole damage from flea beetles

 

Figure 5. Green peach aphid.

Figure 5. Green peach aphid.

 

Figure 6. Green peach aphid colony.

Figure 6. Green peach aphid colony.

 

Figure 7. Cabbage aphid colony.

Figure 7. Cabbage aphid colony.

 

Figure 8. Striped cucumber beetle

Figure 8. Striped cucumber beetle.

 

Figure 9. Adult squash bug

Figure 9. Adult squash bug

 

Figure 10. Squash bug egg mass.

Figure 10. Squash bug egg mass.

 

Figure 11. Spider mites.

Figure 11. Spider mites.

 

Table 2: Diseases

Disease
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)
(Order this publication)
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)
(Order this publication)
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)
(Order this publication)
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)
(Order this publication)
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)
(Order this publication)

Powdery mildew
(Sphaerotheca spp.)

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
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

Anthracnose (Colletotrichum pisi)

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 12. Powdery mildew.

 

Figure 13. Anthracnose on snow pea

Figure 13. Anthracnose on snow pea

Table 3: Physiological Disorders

Disorder
Crop(s) Affected
Symptoms
Monitoring
Management
Reference Figure(s)

Nutrient deficiencies

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
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

Herbicide Injury

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
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 14. Boron deficiency in lo bok

 

Figure 15. Magnesium deficiency symptoms on radish

Figure 15. Magnesium deficiency symptoms on radish

 

Figure 16. Nitrogen and/or phosphorous deficiency symptoms on gai lan

Figure 16. Nitrogen and/or phosphorous deficiency symptoms on gai lan

 

Figure 17. Trifluralin injury on yow choy (centre row)

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

Other OMAFRA Resources


For more information:
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E-mail: ag.info.omafra@ontario.ca