PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
San Jose scale
An example of an armoured scale (Family Diaspididae)
A major pest of deciduous fruit trees throughout
the world. Minor pest in SE Qld, Vic and WA.
Scientific name
Quadraspidiotus perniciosus (Order Hemiptera),
an armoured scale, sometimes called a hard scale).
Host range
Wide range of deciduous fruits and trees and
shrubs, other plants, including:
Fruit, eg especially pome fruit, eg apple, pear,
quince, and stone fruit, eg almond, apricot, cherry,
peach, plum. Not usually citrus.
Ornamentals, eg the flowering species of pome
and stone fruits, also many introduced trees and
shrubs, eg hawthorn, willow.
Other crops, eg hedges of tree lucerne may
become seriously infested.
Description & damage
Adult females are yellow, about the size of a
pin head, soft bodied and concealed by a roughly
circular 2 mm diameter grey-brown scale covering.
The male scale covering is smaller and oval in
shape with a raised dot near the larger end of the
scale. The adult male emerges from the scale
covering as a minute, winged insect. Scales can
overlap. Nymphs (crawlers) are active, 6-legged
and yellow. These settle near the adult, insert their
long tube-like mouthparts into the sap, lose their
legs and begin secreting their scale covering.
Twigs, limbs and trunks. This scale is
found principally on the trunk, branches and twigs
of deciduous trees. Small circular gray scales can
be seen on the base of young shoots, originating
from main branches. Nymphs and adults damage
plants by sucking sap mainly through the bark and
injecting a substance toxic to the plant.
Poor growth, dead or rough, cracked twigs
Infested plants may suffer water stress.
Young trees can be quickly killed by heavy
populations of scales on the trunk and limbs.
Limbs and twigs heavily infested with scale
may die during the growing season, especially in
autumn. The following spring, shoots develop
below dead branches; the framework of young
trees may be seriously affected.
Little or no honeydew is produced.
Bark is rough, pink or ashy due to the masses of
tiny difficult-to-see scale coverings. The purplish
colour is similar to the colour of the bark. Pink
or red spots about 1 mm in diameter surrounded
by a white halo develop around each gray scale.
Gum droplets occur on branches of stone fruit.
Fruit, especially apples and pears, develop
characteristic pink or red spots about 1 mm in
diameter surrounded by a white halo. One tiny
scale is in the center of each reddish spot. Other
scale insects may produce the same reaction.
Cherry fruit are infested mostly at the calyx end.
Leaves may also be infested, usually with male
scales. Look for look for yellowish areas on leaves
where scale have settled, leaves which fall and
twigs and stems dying.
General. Small populations cause debilitation
and aesthetic value. Once established it usually
increases very rapidly and may seriously injure
or kill the tree over a period of several years
Examine closely the photographs on
the previous page to appreciate how
tiny the scales are, they are easily
overlooked on twigs and branches
Fig. 114. San Jose scale
(Quadraspidiotus perniciosus).
Photo NSW Dept of Industry and Investment (E.H.Zeck).
All enlarged x35
2. 2 nd -stage nymph
3. Adult female
4. Scale covering of male
5. Scale covering of female
Actual size
6. Scale on twigs and leaves
168 Insects and allied pests - Hemiptera (bugs, aphids, etc)