Bulletin 25 2010 - BSES

MONiTOriNG
Childers canegrub life cycle
Eggs Early instars
Late instars
Dec
Jan -
Mar
GRUB
SAMPLE
Apr -
May Jun -
Sep
Oct -
Apr
DAMAGE
SURVEY
Monitoring allows growers to make
informed decisions on future canegrub
management. The process could involve
monitoring numbers of canegrubs or signs
of their presence– ideally it would be best
to monitor both numbers of grubs and
levels of damage.
A monitoring system for greyback
canegrub in central and northern
Queensland is outlined in the
GrubPlan 2007 booklet, available on the
BSES website. We have developed models
to predict numbers of greyback canegrubs
one year ahead, using monitoring
information. Grower groups near Mackay
(Mount Kinchant) and Gordonvale have
been testing this system over the past two
years while a new group is starting this
year in the Herbert – all with funding
from SRDC.
In southern Queensland, there are
numerous types of canegrubs with either
1-year or 2-year life cycles. In the past,
monitoring of 2-year species such as
Childers canegrub in ratoons has focused
on checking for grubs in spring, after
harvest. The disadvantage of monitoring
grubs in spring is that there is little time
May -
Sep
Oct Nov
Adults fly Egg
lay
Dec
Pupation
3 4
fIGuRE 3
Grubs/stool - Spring
10
Timing of monitoring and damage
assessment for Childers canegrub.
fIGuRE 4
Strong relationship between numbers
of Childers canegrubs counted in
canefields in autumn and the following
spring-summer, 2005.
IMAGE 5
Greyback cane beetles feeding on fig
tree leaves.
for planning management strategies,
and significant crop damage has already
occured by the time grubs are detected or
insecticide is applied.
A more effective monitoring system
relies on sampling Childers canegrubs in
autumn rather than at the traditional
time in spring – see figure 3.
Detection of grubs in autumn gives plenty
of opportunity for the grower to decide
the most cost-effective option (treat or not
treat, or fallow-crop) and to coordinate
harvest date with the chosen treatment
option as well as other cropping activities
such as fertilising, irrigation and weed
management.
large numbers of Childers canegrubs in
autumn indicate an imperative to harvest
that block reasonably early and then
to treat it immediately, or alternatively
develop another cropping plan.
The correlation between numbers of small
Childers canegrubs that we have found in
autumn and then subsequent numbers of
large damaging grubs in spring-summer has
been strong enough to guide management
decisions – see figure 4.
Monitoring results for southern 1-year
canegrub (a 1-year species) must be
8
6
4
2
R
0
0 2 4 6 8 10
Grubs/stool - Autumn
2 = 0.7257
interpreted differently from results with
Childers canegrub. With southern 1-year
canegrub, the grubs counted in autumn
are a different generation from those
that may damage the cane the next
season. However numbers of southern
1-year canegrub usually increase from
year to year if unchecked, so grubs in
moderate numbers this year often spell
trouble for next year.
An SRDC-funded grower group at Isis will
further test these monitoring systems for
Childers and southern 1-year canegrubs
over the next 2 years.
Acknowledgment: This project was
funded by BSES limited, SRDC, and the
Queensland Government through the
Department of Employment, Economic
Development and Innovation.
[A monitoring
system for greyback
canegrub in central
and northern
Queensland is
outlined in the
GrubPlan 2007
booklet, available
on the BSES
website.]
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