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Lygus bugs have piercing and sucking mouthparts that physically damage the
plants by puncturing the tissue when they suck plant juices. The plants also react to the
toxic saliva that the insects inject when they feed.
Host Crops
Lygus and other plant bugs feed on weeds (chickweed, dandelion, red clover, red root
pigweed, lamb's quarters, plantain, golden rod, asters), forage crops (red clover,
alfalfa), oilseed crops (canola, mustard, sunflower), vegetables (asparagus, beans, beets,
cabbage, cucumbers, peppers, potatoes, sugar beets, tomatoes, turnips) and fruits
(strawberries, apples).
Biology
Adult lygus bugs are about 5 mm (1/4 in.) long and 2.5 mm (1/8 in.) wide, oval, and
slightly flattened. They vary in colour from pale green to reddish-brown and have a
distinctive triangle or "V" mark about one-third of the distance down the back,
just in front of the wings. The legs and antennae are relatively long.
The young nymphs are pale-green in colour and look like aphids except that they are
more active. Colour in the older nymphs becomes more variable and is similar to that of
the adults. The older nymphs develop prominent black dots on the top of the thorax and
abdomen.
The adults overwinter, hidden in protective hedgerows, fallen leaves and other plant
debris. Emerging in mid-April to late May, they feed on host weeds. The eggs are laid on
the stems and petioles of these hosts. About 10 days later, the eggs hatch and the nymphs
feed.
The 1st-generation adults appear in mid-June to mid-July. They leave the host weeds,
dispersing into adjacent crops. The 2nd-generation nymphs feed on the host plants during
August, causing economic damage. The adults produced by this generation emerge in late
August and September. A smaller 3rd generation may emerge in September.
| May |
June |
July |
August |
September |
| Overwintering adults become active, feed, lay eggs |
Nymphs feed, new adults emerge |
New adults mate, feed, lay eggs, nymphs feed |
Nymphs feed, new adults emerge |
Adults begin to overwinter |
Scouting Techniques
Monitoring for lygus in most crops usually involves a combination of sweeping nearby
host weeds, using a standard insect sweep net, and visually inspecting crop plants.
Tapping blossoms over a shallow, white pan will reveal any young nymphs present.
Monitoring for lygus in canola involves sweeping either with
ten sweeps in 15 locations
or 20 sweeps in 10 locations in the field. The locations should be representative of the
field and spaced about 50 metres (150 ft.) apart. For those people who may have trouble
separating lygus nymphs from aphids, a hand magnifier is recommended.
Economic Thresholds
In canola, there are two economic thresholds:
-
When sampling up until petal fall is
complete, the threshold is an average of 15 lygus per ten sweeps
-
If sampling is within four to five days after petal fall, the threshold is an average of 20 lygus
per ten sweeps
In alfalfa grown for seed (not forage), an average of
five nymphs per sweep or one adult per
two sweeps indicates an economic infestation. Control is not recommended in alfalfa grown
for hay.
Control Tips
Reducing adjacent weedy areas that serve as overwintering sites for the adults and
reducing weeds in crops that serve as early season hosts will lower local populations.
Because plant bugs have two generations throughout most of the their range in the
southern Prairies, two insecticide treatments may be necessary.
If insecticide is required during the bloom stage, early morning or late evening
applications should be targeted to minimize possible bee kill. In canola, spraying is best
done at "post-petal fall" to minimize the effects of the insecticide on
pollinators. |
