PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Black scale
An example of a soft scale (Family Coccidae)
Scientific name
Saissetia oleae (Order Hemiptera), sometimes
called brown olive scale. Widespread, common.
Key pest in Qld, NSW, Vic, NT and WA. See page
144 for other soft scales.
Host range
Wide range of plants. Mostly woody plants, but
occasionally found on succulent hosts, eg vines,
geraniums, watermelon.
Ornamentals, eg gardenia, holly, house plants.
hibiscus, oleander, poplar, tamarisk.
Fruit crops, eg especially citrus, also apricot,
passionvine, olive, vines, apple, pear, plum.
Description & damage
Adult female scales are stationary and tend
to cluster in small colonies on various parts of the
plant. They are dark brown, bun-shaped, and about
3 mm long and 2 mm wide (Fig. 112). The surface
is smooth but ridges on their back form a raised
'H' pattern, particularly on young adult scales.
Young adult females, before egg laying, are dark
mottled grey, softer and less humped than later and
are often called the ‘rubber’ stage. Male scales
are narrower, flat, tiny, winged and rarely seen.
Nymphs are initially light brown or pink and
about 0.5 mm long. Newly hatched ‘crawlers’
move around for 12-24 hours in search of food
then settle permanently along veins of young
leaves. Older stages look like adult females but
are paler.
Honeydew, sooty mould and ants...
Plant damage caused by nymphs and adults sucking
plant sap is often not great. It is the production of
copious amounts of honeydew by the young scales
with the resultant growth of sooty mould which
causes the greatest problem. Ants are attracted to
honeydew especially when eggs hatch into crawlers.
Ants feed on the honeydew protecting the scales
from natural enemies and help spread the crawlers
from plant to plant.
Leaves, twigs and stems. Although all
stages are found on branches, twigs, stems, stalks,
leaf midribs and young fruit, twigs and stems are
preferred. Soft scales feeding on young tissue can
produce distorted foliage and yellowing of foliage.
Heavy infestation can cause twigs and branches to
die back. Leaves drop if infestation is heavy.
Fruit. Citrus fruit are greenish where scales were
attached, and if covered with scales or sooty
mould, are difficult to clean before packing,
especially if skin is rough, eg mandarins.
General. Extensive sooty mould can reduce
photosynthesis and tree vigour. Soft scales can be
major economic pests, eg grapevine scale,
(Parthenolecanium persicae) on grapevines, but
not all scales are economic pests (Buchan 2008).
Diagnostics.
Soft scale are so named because most species
have bodies that are exposed and ‘soft’ but in many
cases, mature females are not the least bit soft, upon
maturing their skin becomes hardened serving as a
shell for eggs shell for the eggs and young.
Adult females are generally large, obvious and
are easy to recognize on stems. They are domeshaped
and about the size of a match head. The
tiny eggs laid under the female look like piles of
very find sand. Black scale may be confused in
the juvenile stages with citricola, hemispherical
and soft brown scales. After the 2 nd moult black
scale can be recognized by the characteristic ‘H’
pattern on its back.
Scale covers or ovisacs may remain on twigs
long after scales have died. Squash the scale
between the fingers to see if it is alive, if alive
your fingers will be wet from the juice squeezed
out, if dead you fingers will be dry and dusty.
Increased ant activity, eg aggressive meat ants
(Iridomyrmex spp.) protect scales and other
honeydew producing insects.
Soft scale produce large amounts of honeydew
one sure sign is the presence of honeydew so if
you see that or sooty mould look for a culprit.
Lucid Keys www.lucidcentral.com/ and search for:
Scale Insects: Identification Tools for Species of
Quarantine Significance
Fig. 112. Black scale (Saissetia oleae).
PhotoNSW Dept of Industry and Investment (E.H.Zeck).
Enlarged x24
1. Eggs
st
2. 1 stage female or "crawler"
Enlarged x12
3. 2 nd stage female
4. Adult female (top view)
5. Adult female (side view
Actual size
6. Scales and sooty on citrus shoots, leaves
164 Insects and allied pests - Hemiptera (bugs, aphids, etc)