PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Pest cycle
There is a complete metamorphosis (egg,
larva - curl grub, scarab grub, pupa and adult) with
only 1 generation each 1-3 years. In spring female
beetles, seek out egg laying sites usually near the
soil surface of well watered fine open textured turf.
Eggs hatch in Jan-Feb, larvae burrow and feed just
below the soil surface on organic matter. Towards
autumn larvae move deeper into the soil and feed
on grass roots. At the start of winter, larvae feed
less actively and burrow even deeper into the soil.
During late spring they pupate and in summer
(Dec.-Jan.) adults emerge, fly off to favored host
plants, mate and start egg laying. All scarabs have
a similar life cycle, eg 1 year - black beetle,
pasture cockchafer, pruinose scarab, Argentinian
scarab and pasture scarab; 2 years - Christmas
beetle. Timing of the life cycle varies between
species and is affected by climatic conditions.
‘Overwintering’
As larvae deep in the soil in special chambers.
Spread
Adults can fly long distances.
Adults of some species may crawl in from
nearby areas or be transported in flood water.
Larvae may be spread in containers and bush
litter used as mulch.
Conditions favoring
Numbers are regulated by weather, natural
enemies, eg birds, diseases.
Beetles favour well watered lawns of fine textured
grasses and open textured soil for egg laying.
Street lights attract beetles which may burrow in
soil under the lights in an attempt to lay eggs.
Severe damage usually occurs during autumn.
Planting crops, eg pineapple, strawberry, nursery
stock, vegetables, in recently-ploughed pasture
or grassland containing paspalum, a favoured
food. Improved pastures.
Severe defoliation of trees by adults usually only
occurs when moist soil favour emergence of
large numbers of adults (drought hardens soil,
newly formed beetles die in their chambers).
Management (IPM)
Are you a commercial grower or home gardener?
1.Obtain/prepare a plan that fits your situation,
based on the previous season's records of infestation.
2.Crop, region. Turf, pasture, eastern states, etc.
3.Identification can be difficult at the grub stage so
consult a diagnostic service (see page xiv) to ensure
correct control methods for your scarab grub, eg
Argentine scarab beetle is the main pest species in the
ACT and African Black beetle in Vic.
4.Monitor scarab grub numbers by soil plugs in
October to indicate need for treatment. In high priority
areas also monitor adults at egg laying time with light
traps. Also check bird activity. Record findings.
5.Threshold will vary with crop, locality and likely
economic damage (page 39). How much damage is
acceptable? For many crops, thresholds have not been
determined.
As many as 250 scarab grubs/square meter have been
recorded in the ACT. Overseas recommendations
suggest that pesticides are only necessary if there are
6 or more scarab grubs in an area 30 cm by 30 cm
square by 5-8 cm deep. Since larvae live in soil under
the plants, it is always difficult to know how many
are present. Generally the first sign of infestation is
the symptoms produced on the plant.
A population of about 5 mature larvae per pineapple
plant produces visible wilting and yellowing.
3 or more per strawberry plant - grower is not
aware of them until plants start to show symptoms.
6.Action. Good cultural methods can reduce
populations of grubs and reduce damage.
Remember by the time damage is apparent it is too
late to apply chemicals.
With some crops treat preplant as it is impossible to
treat after planting.
For some crops economic injury levels have not
been established and there may be no satisfactory
means of controlling these pests.
7.Evaluation. Review IPM program to see how well
it worked. Recommend improvements if required, eg
use of more tolerant varieties, and compare the current
seasons data with previous ones.
Fig. 76. African black beetle
(Heteronychus arator). PhotoNSW
Dept of Industry and Investment (E.H.Zeck).
Enlarged about x3.5
1.Eggs in soil
2.
3.Pupa
4.Adult female beetle
5.Adult male beetle, note shape
of front tarsus or foot and
damaged maize stem
Actual size
6.Eggs
7.
8.Pupa
9.Beetle and young maize plants
that have been attacked
Insects and allied pests - Coleoptera (beetles, weevils) 109