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Insects, Diseases and Disorders
of Asian Vegetables
Table of Contents
- Introduction
- Table 1: Insects
- Table 2: Diseases
- Table 3: Physiological Disorders
- Summary of the Tables
- Related Factsheets
- 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
|
|
|
|
|
Diamondback moth larvae, imported cabbageworm,
cabbage looper
(Plutella xylostella, Artogeia rapae, Trichoplusia
ni)
|
As above
|
-
feeding holes in leaves
-
frass (insect droppings)
|
|
|
|
|
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
|
|
|
|
|
Cutworms
(Noctuidae)
|
All crops
|
|
|
|
|
|
Leafminers
(Liriomyza spp.)
|
Gai lan, yow choy, choy sum, bok choy, pak
choy, chrysanthemum greens, malabar spinach, fuzzy squash,
bitter melon
|
|
|
-
greenhouse sanitation
-
crop rotation
-
weed control
-
biological control
-
registered insecticides
|
|
Aphids
(Myzus persicae, Brevicoryne brassicae, Aphis gossypii)
|
All crops
|
|
|
-
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
|
|
|
|
Squash bug
(Anasa tristis).
|
As above.
|
|
-
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
|
|
|
-
crop rotation
-
field sanitation
-
naturally occurring predators and parasites
(rove beetles, predatory flies, etc.)
-
row covers on small plantings
|
|
|
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
|
|
|
biological control (predatory mites)
|
|
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
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
|
Bacterial
Diseases of Cruciferous Crops
(Order No. 86-046) and 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
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
|
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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 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
Other OMAFRA Resources
For more information:
Toll Free: 1-877-424-1300
Local: (519) 826-4047
E-mail: ag.info.omafra@ontario.ca
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