Agriculture Reference
In-Depth Information
seed-coating, control was achieved with only 15% the AI/ha needed for an
equivalent in-furrow treatment. The low insecticide doses needed when using
seed-coating minimize the risks associated with insecticide contamination,
including the destruction of beneficial insects and the exposure of field workers
to toxic substances during in-furrow treatments.
Aerial sprays of insecticides are also used to destroy egg-laying females. By
monitoring the insects caught in traps, it has been possible to restrict spraying
to periods when egg-laying adults are infesting onion crops (Lorbeer
et al
.,
2002). The traps are made of highly reflective white, yellow or blue sticky
plastic sheets baited with volatile attractants like Pr
2
S
2
(see above). Using these
IPM techniques, the number of sprays in Ontario was reduced from around ten
per season to just two. The time to start monitoring can be determined from
temperature records and knowledge of thermal time requirements for egg-
laying adults to develop (see Table 5.2).
This predictive system was found unsatisfactory for Germany, and a more
complex model has been developed that predicts the progress of cohort insects
through each developmental stage until the egg-laying adults are in flight (Otto
and Hommes, 2000). This model was based on the relationships between
temperature and development rate shown in Fig. 5.9, with pupal development
arrested by diapause (see above) if mean soil temperatures are below or above
specified limits at the appropriate times of year. The model specifies that flight
activity of adults is maximal at mean wind speeds of 3 m/s and below, and
declines linearly to zero with increasing mean wind speeds between 3 and 8 m/s.
Predictions of adult fly infestation in the two main chive-growing regions
of Germany corresponded fairly well with monitored populations for the first
two of the annual generations, but accumulated errors made the prediction of
the third generation unsatisfactory. The model was entered for further testing
within a suite of computerized decision aids for plant protection used by the
German crop extension services.
Soni and Ellis (1990) have reviewed the additional aspects of control that
are important within an IPM strategy. These include the destruction of infested
Table 5.2.
The thermal time above a base temperature of 4.4°C
needed to complete the development of each life stage of the
onion fly,
Delia antiqua
, in Ontario, Canada (from Liu
et al
., 1982).
Thermal time
Life cycle stage
needed (°C days)
Egg
50
Larva
287
Pupa
306
Adult, pre-egg-laying
103
Generation time (egg to egg)
746
