Pest management - Ecological Applications: Toward a Sustainable World - page 166

insecticides when in the potato tuber, so control must be applied to leaf-mining
generations. The IPM strategy for potato tuber moth (Herman, 2000) involves moni-
toring (female pheromone traps, set weekly from mid summer, are used to attract
males, which are counted), cultural methods (the soil is cultivated to prevent soil
cracking, soil ridges are molded up more than once, and soil moisture is main-
tained), and the use of insecticides, but only when absolutely necessary (most com-
monly the organophosphate, methamidophos). Farmers follow the decision tree
shown in Figure 6.14.

6.5.2 IPM against an
invasive weed in
Australia

A more quantitatively based attempt to defi ne an IPM system concerns the thicket-
forming weed Mimosa pigra in Australia. You learnt in Section 6.3.1 that several
biological control agents have been released, but so far without much success.
Buckley et al. (2004) considered biological control, along with all other conceivable
weed management approaches, and assessed their likely value by means of a simula-
tion model. (This has much in common with the population viability analyses dis-
cussed in the context of species conservation in Chapter 5.) Realistic parameters
were included in the model (defi ning seed production, seed-bank properties, seed
dispersal, germination, seedling survival, weed longevity, time to reproduction, etc.)
and simulations were run for the following scenarios:
1 Disturbance alone - note that native vegetation can outcompete the weed in the
absence of disturbance by fi re or by water buffalo Bubalus bubalis .
2 Physical and chemical control alone - note that small isolated infestations can be
eradicated by hand-pulling, cutting or herbicides but this approach may need to be
prolonged because of regrowth from the base of the plant.

Fig. 6.14 Decision fl ow
chart for the integrated
pest management of
potato tuber moths
(PTM) in New Zealand.
Boxed phrases are
questions (e.g. 'what is
the growth stage of the
crop?'), words in arrows
are the farmer's answers
to the questions (e.g.
'before the tuber has
formed') and the
recommended action is
shown in the vertical
box (e.g. 'don't spray
the crop'). Note that
February is late
summer in New
Zealand. (From Begon
et al., 2006, based on
Herman, 2000.)

Growth stage
of crop?

Pre-tuber

D
O

N
O
T Time of

year?

Pre-February

S
P
R
A
Y

Prevailing
weather?

Cool/wet

PTM
population?

Increasing

S
P
R
A
Y

Breaking open

Molds?

Possible to
use cultural
controls?

If not possible