PEST
THRESHOLDS
Pest Detection and Targeted Control.
The indiscriminate use of agrochemicals is self-evident and
so it is necessary to adopt a targeted pest and disease control
policy. The principles of integrated control need to be respected
and known thresholds for spray applications need to be taken
into account. The economic threshold is attained if the monetary
benefits of a certain treatment exceed its costs. The uses of
spray thresholds assume knowledge of pest population densities,
the damage they may inflict and suitable methods of control
for each pest
How do we measure thresholds?
Yellow dish traps are used to detect the first approaches and
flying activity of injurious insects (weevils, beetles etc.).These
are placed in the crop about 20m from headlands and at a height
above ground determined by the growth of the crop. On large
fields, placing these off each headland will be beneficial.
The dishes should be examined at regular intervals and preferably
near mid-day. Additional population densities (number of insects/plant)
obtained by shaking racemes over a white tray would help back
up the dish findings.
Pest
Thresholds.
Pollen beetle. 15-20 per plant during green to
yellow bud.(winter rape). If flowering protracted as low as
5 may be the economic threshold.
Cabbage
seed weevil. 1-2 per plant during flowering.
Winter
stem weevil/cabbage stem flea beetle. Treat if more
than 5% of plants infested with the weevil larvae or where there
is more than five larvae/plant of the flea beetle larvae.
Cabbage
mealy aphid. No threshold.
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