Insecticides
377
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Safety - page 25 • First aid - page 33 • Resistance management - page 41
Notification is a two-way street – both the beekeeper
and farmer have to make efforts to protect pollinators.
Note: In many cases, beekeepers cannot move or
cover their bees, especially during honey flow, so
timing and accuracy of an insecticide application, plus
selection of the safest insecticide where there is risk
to bees, are the only ways to safeguard bees.
Livestock and residues
The number of days between the application of an
insecticide and harvesting, feeding to livestock or
grazing is given on the label. These restrictions must
be followed to prevent illegal residues in crops and
livestock and to eliminate hazards to consumers.
The guide
This guide only includes the major insecticides
registered for use on field crops in Alberta. Not all
insects controlled are listed for each insecticide.
Economic threshold
Before making a decision to apply an insecticide,
producers need to know if the application would be
economically justified. In addition to the expected
dollar value of the crop, the producer needs to
determine whether the insects present will cause a
yield loss greater in value than the cost of control.
The economic thresholds listed below will assist in
making this decision.
Thresholds are given as the number of insects/unit
of measure (such as #/plant or #/m
2
)
or, for insects
that are difficult to sample, the amount of damage
evident. Chemical controls are generally only
warranted when numbers meet or exceed the
threshold level. Remember to sample throughout
the field (minimum of 10 samples per 160 acres)
to obtain an average infestation level.
Economic Thresholds for Insect Pests of Forage and Special Crops
Insect
Economic threshold
Comments
Alfalfa weevil
Alfalfa hay crops: Thresholds are based on plant
height and number of larvae: < 30 cm - 1 larva per
stem; <40 cm 2 larvae/stem. 3 larvae per stem
requires control regardless of plant height. Alfalfa
seed crops: 20 - 30 larvae per 90° sweep or when
35 - 50%
of foliage tips show damage.
Alfalfa hay crops: If feeding damage
detected cutting hay early can be an
effective control strategy.
Grasshoppers
Alfalfa: See Cereals table.
Lygus bugs
For adults and nymph stages 4 and 5: 2 - 3 lygus per
90
°
sweep.
Nymph stages 1, 2 and 3 do not cause
economic damage.
Pea aphid
Alfalfa: 75 - 100 aphids per plant.
Field peas: 2 - 3 aphids per 20 cm stem tip when
50%
of plants have developed some young pods.
Plant bugs
Alfalfa for seed: 5 nymphs per sweep (any or all
species of plant bugs) when alfalfa is in bud or
bloom.
Sweetclover weevil
Seedling crop (cotyledon stage): 1 weevil per
5
seedlings under slow growing conditions or
1
weevil per 3 seedlings under normal
growing conditions.
Newly emerged 2nd-year stand:
9 - 12
weevils per plant.