Environmental Engineering Reference
In-Depth Information
Table 2.4
Number of granules applied per metre of row for the 10G formulation of carbofuran.
Numbers represent registered use patterns in Canada prior to the product being cancelled in 1995
Rate of application of
the granular formulation
(g/100m of row)
Equivalent rate
of application
(kg a.i./ha)
Number of granules
applied per metre
of row
Usual row
spacing (cm)
Crop
Maize (fi eld,
sweet, silage)
110
75
1.47
3438
Onion (dry from
seed)
70
40
1.75
2188
Potato
300
90
3.33
9375
Rutabaga, turnip
175
70
2.50
5469
Sugar beet
50
60
0.83
1563
granule may well kill a bird; Table 2.4. As we can see, almost 10 000 granules may be applied in just
one metre of crop row.
In maize, the most effi cient implement available for delivering a banded application (a subsurface
T-band application) typically leaves 6.5 to 8.1% of granules at the soil surface (Mineau and Clark
2008). Over 50% of granules are left on the surface at turn points (at the row ends) and automatic
shut off systems can only bring this number down by one half (Mineau and Clark 2008). Surface
banding of granules, followed by more standard covering techniques using rakes, tines, chains, etc.,
can leave up to 40% on the surface. Given the number of granules applied, their attractiveness to
birds, and the fact that a single granule may be lethal, it is not surprising that granular carbofuran has
proven so effi cient at killing birds (see Chapter 8).
In a laboratory study, Kenaga (1974) reported that northern bobwhite given
ad libitum
(i.e., unre-
stricted) access to clean (pesticide free) clay granules, consumed up to 4.9 g/week or 0.70 g/day.
Given that each granule weighed about 0.064 mg (Hill and Camardese 1984), this would correspond
to approximately 11 000 granules ingested per day. By weight, this would represent approxi-
mately 2 200 Furadan 10G granules, or just over 300 larger Furadan CR-10 granules. However, this
extremely high consumption rate for clay granules is not typical of other grit types, which may be
less prone to rapid breakdown (i.e., hard/quartz gravel).
The ingestion of granules and dietary grit by birds in the fi eld has been investigated in a sys-
tematic fashion (Best and Gionfriddo 1991a, 1991b; Best 1992; Best and Fischer 1992). It is now
apparent that silica-based granules (such as most of the carbofuran products sold worldwide) are
extremely attractive to birds. Silicates, quartz, and feldspar are the most commonly sought after grit
material in wild passerines, although this will obviously depend on local availability. The fact that
carbofuran 10G or 15G tends to be much more spherical than 'typical' grit material does not seem
to deter birds. Corncob granules such as carbofuran CR-10 also tend to resist breakdown in the
gizzard, and therefore may be retained in this part of the digestive tract (as is grit). Given the choice,
birds may select harder grit, and therefore reduce their overall consumption. Both silica and corncob
carbofuran granule formulations tend to resist breakdown in the fi eld, and are therefore available to
birds for longer periods of time (Fischer and Best 1995).
In one study undertaken in Utah cornfi elds (see Chapter 8), 831 horned larks (
Eremophila alpes-
tris
) and 81 individuals from other species were found dead following the ingestion of either the 10G
or 15G formulation (FMC 1983). The number of granules ingested was recorded for all carcasses
with intact gastrointestinal tracts. The results by species are given in Table 2.5. This sample is known
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