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Insects,Diseases and Disorders
of Asian Vegetables
Table of Contents
- Introduction
- Related Factsheets
- Other OMAFRA Products
- Table 1: Insects
- Table 2: Diseases
- Table 3: Physiological Disorders
- Summary of the Tables
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 OMAF 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 OMAF Factsheets and publications for more information that
may be applicable to specific groups of Asian vegetables.
Related Factsheets
- Aphids Infesting Lettuce
& Celery in Ontario, (Order No. 00-053)
- Bacterial Diseases of Cruciferous
Crops, (Order No. 86-046)
- Caterpillar Pests of Cruciferous
Crops, (Order No. 99-035)
- Chinese Cabbage Production in Southern Ontario, (Order No. 86-090)
(Order this factsheet).
- Fungal Diseases of Cruciferous
Crops, (Order No. 85-043)
- Leafminers Attacking Field
Vegetables and Greenhouse Crops, (Order No. 00-039)
- Managing Cutworms in Vegetable
Crops, (Order No. 00-055)
- Onion Maggot Control,
(Order No. 00-017)
- Pumpkin and Squash Production,
(Order No. 00-031)
- Tarnished Plant Bug Damage
on Vegetable Crops in Ontario, (Order No. 98-025)
Other OMAF Resources
Integrated
Pest Management for Crucifers (booklet plus video), Order Number VID012
with specific reference to some Asian crucifers (Order
this publication).
Publication 363, Vegetable Production Recommendations, with specific
section on 'specialty vegetables'. (Order
this publication)
Vegetable Web site.
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 IPM booklet/video, Order No. VID012
(Order this video) |
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 IPM booklet/video, Order No. VID012
(Order this video) |
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
|
Refer to IPM booklet/video, Order No. VID012 (Order
this video) |
| 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
|
Refer to IPM booklet/video, Order No. VID012
(Order this video)
|
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 IPM booklet/video, Order No. VID012
(Order this video)
|
|
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
|
|
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.
For more information:
Toll Free: 1-877-424-1300
Local: (519) 826-4047
E-mail: ag.info.omafra@ontario.ca
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