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 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

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

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)

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
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

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

Insect Crop(s) Affected Symptoms Monitoring Management References/
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
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

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
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 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