Toward new sowing systems for
aerial baiting.
Landcare Research Workshop, Lincoln,
16 November 2009
G. Nugent
Landcare Research P.O.Box 40, Lincoln
Aerial baiting
• Cheapest baiting system
• Since 1990s GPS guided
helicopters using buckets with
spinners to broadcast bait has
become the norm
Fixed wing rarely used now
Driven by belief that thin even
spread of bait by broadcasting
has to be best (less chance of
bait gaps)
Results in very limited ability
to precisely control bait
placement (equated by some
to carpet bombing)
Otago Daily Times 21/01/2008
Threats to aerial baiting
• 1080 poisoning controversial - environmental
contamination, non-target by kill, not most humane
– Continued use requires reducing the actual and perceived risks
– Ideally should use far less 1080, less often
Our core question:
• Can sowing rates be reduced much more?
– Simple calculations suggest YES
– Usually only <10 possums+rats per ha yet 200-500 individually
lethal baits/ha usually sown
=> Why is such overbaiting needed?
Fragmentation hypothesis
• GPS-guided baiting ensures all
possums encounter toxic bait, but
some still survive because they
need to quickly encounter 2 or
more baits to be killed
– This need v is because possums have to find a lethal
dose within 30-60 minutes
– And some sub-lethal bait fragments are produced
during (or after) sowing
=> High bait density (and/or prefeeding) is needed to
ensure high encounter rate
New Creek 2008
12g RS5,150m swath,
fast spinner
(NB: worst example),
=> shows lots of very
small 0-2g fragments
created during (or after)
sowing
Fragmentation
Evidence
RS5 bait distribution before sowing
0
10
20
30
0-1 2-3 4-5 6-7 8-9 10-11 12-13 >14
weight (g)
% o
f b
ait
s
RS5 bait distribution after sowing (on road)
0
10
20
30
40
0-1 2-3 4-5 6-7 8-9 10-11 12-13 >14
weight (g)
% o
f b
ait
s
Coverage question
• If overbaiting needed
because of fragments, is a
high bait density needed
everywhere?
=> What if bait was sown in
high density strips or
clusters rather than
broadcast?
Broadcast flight path map
showing total coverage,
Molesworth, 2008
How does fragmentation occur?
• Three possibilities
– Before sowing
– During sowing
– After sowing
How does fragmentation occur before sowing?
• Fracture lines created during extrusions
– Baits simply crumble under weight/pressure
• Rough handling/abrasion in in bags
– Knocks ends off baits
• Some pellets break apart during pouring into hoppers, or
larger containers
– Some evidence this is worse for RS5 and where bait is stored for
long periods
– Possibly/probably worse if bait softened by previous dampening
(e.g. w deer repellent)
How does
fragmentation
occur before
sowing?
• Counterproductive focus
on efficiency through
mass handling
•Not suited to current bait
types
•But ok w shatterproof bait
How does fragmentation occur during sowing?
• As they tumble down the
bait column in the hopper
– Lot of pressure on baits at
bottom of bug hoppers
• As they hit the high speed
spinner
– The higher the speed the
worse the problem
• As they hit bucket legs
(where not retractable)
Spinner 1350 rpm
0
50
100
-100 -50 0 50 100
Distance from flight path (m)
N b
ait
s
Spinner 950 rpm
0
50
100
-100 -50 0 50 100
N b
ait
s
All apple eaten
0
50
100
Unp
oiso
ned
3.0k
g/br
oadc
ast
0.25
kg/a
ligne
d
0.25
kg n
ot a
ligne
d
Carrot
Apple
Cereal
All carrot eaten
0
50
100
Unp
oiso
ned
3.0k
g/br
oadc
ast
0.25
kg/a
ligne
d
0.25
kg n
ot a
ligne
d
Carrot
Apple
Cereal
How does fragmentation occur after sowing?
• Partial consumption by rats/mice?
Fragments left by a possum
How does fragmentation occur after sowing?
• Competition between possums for a single bait
How does fragmentation occur after sowing?
• Caching by rats/mice may quickly reduce the amount of bait
available – decrease possum encounter rate?
Possums
0% 2% 4% 6% 8%
Residual mRTCI
Results 1: Whirinaki 2007
• Bait sown aerially in
strips, or broadcast, or
placed by hand in clusters
=> strips and clusters fine
for possums and rats (at
100m flight path spacing)
- with prefeed
- even with only
0.4kg/ha toxic
Complete coverage
not essential for
possums or rats
No Prefeed, 0.4kg/ha clusters
Prefeed, 0.4kg/ha clusters
Prefeed, 2.0kg/ha strips
Prefeed, 2kg/ha broadcast
No prefeed, 2kg/ha broadcast
Aerial sowing
in clusters
• SowLow bucket– Originally designed to
improve control of sowing rate
– previously used with spinner
• Redesigned to sow clusters– Spinner removed, timed
gate added under wheel
– For Molesworth, delivered clusters of 35-40 8g baits every 30m(1kg/ha)
Cluster sowing, Isolated Hill
Results 2: Post-control possum abundance
(RTCI), Molesworth
=> With no prefeed, no consistent difference
between 2.5kg/ha broadcast and 1.0kg/ha cluster
Low coverage treated only habitats with predicted RTCI > 10% RTCI, high coverage treated habitats >5% RTCI
0.8%
1.1%
0.5%
1.8%
0.0%
0% 1% 2% 3% 4% 5%
Broadcast High
Coverage
Broadcast Low
Coverage
Cluster High Coverage
Cluster Low Coverage
Cluster w Prefeed
Residual Trap Catch Index (%)
0.9%
1.1%
0.0%
0% 1% 2% 3% 4% 5%
Broadcast
No Prefeed
Cluster No
Prefeed
Cluster w
Prefeed
Residual Trap Catch Index (%)
Results 3: Landsborough(b) Reduction in CTC activity
0% 50% 100%
Not Aligned
Cluster
Aligned
Cluster
Not Aligned
Broadcast
Reduction in CTCI
(a) Residual Trap Catch
0% 5%
Not Aligned
Cluster
Aligned
Cluster
Not Aligned
Broadcast
RTCI
Std 3kg/ha
broadcast with
no prefeed
alignment
Clustered 0.25
kg/ha with
prefeed
alignment
Clustered 0.25
kg/ha with
no prefeed
alignment
Std 3kg/ha
broadcast with
no prefeed
alignment
Clustered 0.25
kg/ha with
prefeed
alignment
Clustered 0.25
kg/ha with
no prefeed
alignment
Similar kills with either broadcast or cluster+aligned prefeed,
even though 92% less toxic bait used
=> possible to reduce the amount of 1080 by > 95%?
Low Sow summary
• Early days, but it does appear that the amount of 1080
needed can be greatly reduced with some simple
changes in sowing method and how prefeed is used.
potential for major cost savings
should reduce many (but not all) of the actual and
perceived risks associated with this tool
same principles will also make aerial baiting (with 1080
or any other poison, biocontrol, or Tb vaccine) much
cheaper than now
3. New sowing technologies
LR-industry partnership w AHB-funding for field testing– Directions not yet finalised
– Four possibilities to be explored
1. Shatterproof baits - able to
broadcast at low density
Big buckets and helicopters, but no
control of placement
2. Strip sowing of current baits
Fixed wings with 2 tonne hopper fly at
150kph, 150m spacing = >2000ha per
hour – 4000-8000ha per plane load!
New sowing technology (2)
3. Cluster sowing of small 2-4 g baits at low rates (<100g/ha)
small buckets and helicopters -
1000ha/ha = <$1/ha per pass cf $2.50-
$5.00 for current ops.
4. Simultaneous pre-fed in moderate
swaths with clustered toxic
Moderate buckets and helicopters –
single pass = low cost
New sowing technology (3)
Also: GPS control of cluster placement
• GIS/GPS control of bucket gate stops clusters being sown within
(say 50m) of any creek or track designated in the GPS
• Already routine for fertiliser application
• World leading GPS capability in NZ (Tracmap Dunedin and others)
New sowing technology (4)
Aim is to produced a hi-tech precise sowing system that:
– Places a small amount of bait in clusters at known locations
– Puts bait in only 2-3% of the landscape
– Does not not include any mappable waterways or tracks.
Coupled with small bait sizes and ultra-low sow rates
allows small helicopters and should reduce flying and
bait costs greatly.
– Makes more frequent use of aerial poisoning affordable and
yet still uses less 1080 –2-3 year cycle feasible for rats?
– Makes use of expensive toxins affordable
• Cholecalciferol
• New high tech toxins/vaccines/immunocontraceptives
Potential new applications
• Better delivery of old agents
– Screening out fragments at bottom of bucket
• Should be technologically simple?
• Holey converyor belt from buckt to offset spinner?
• Need for fragment reservoir under bucket?
– Need to increase precision of placement
Precise bait placement
The challenge: No 1080 in waterways
Precise
placement
• 50 m either side is too wide?
• Need very low flying
– Just above canopy?
• New very slow flying?
– 20-30knots?
– To minimise bait deviation
from trajectory?
Potential new applications
• Delivery of expensive new agents
– live BCG vaccine in a sachet
• ‘difficult to sow’ bait carriers
– Oral forms of fertility control
– Expensive ‘new’ toxins
• Connovation shatterproof bait
• Chole bait @ $20/kg
• Long life chole gel
Suggested directions
• Industry to work with bait manufacturers on sowing systems for
shatterproof baits
– Further development of current broadcasting technology by industry
• Bigger gentler spinners
• Industry to develop strip and cluster sowing solutions for current
baits
– Gentler spinners
– Optimisation of ability to align prefeed and toxic
– Optimisation of flight path spacing
– Fixed wing solutions?
Suggested directions (2)
• Precise placement of clusters/individual baits at
recorded locations
– LCR + industry + GPS/GIS technologists
– Development of ideal bait for this app.
• 5 g, durable, 0.25% 1080
• Requires long regsitration
• Dual agent or bait type delivery
– LCR + industry