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 fact sheet: 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 fact sheet highlights symptoms, monitoring and potential management strategies for several common Asian vegetables. Refer to the following additional OMAFRA fact sheets 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.)
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
13
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)
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 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:
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.
