PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Woolly aphid
Scientific name
Eriosoma lanigerum (Order Hemiptera).
Woolly aphid is a serious pest of apple trees.
Other aphids also attack apples.
Apple-grass aphid (Rhopalosiphum insertum)
Pear root aphid (E. pyricola)
Spiraea aphid, apple aphid (Aphis spiraecola)
Overseas also Aphis pomi, Dysaphis plantaginea
Host range
Fruit, eg apple, rarely pears. Ornamentals, eg
crab apple, occasionally cotoneaster, hawthorn
(Pyracantha spp.), liquidamber.
Description & damage
Adults are nearly all females and wingless,
however, winged females may be produced in
autumn. Aphids are globular in shape, purplishbrown
and usually covered with long, white woolly
threads which they secrete from pores on the body.
These threads form a loose tangled mass over the
active colonies and act as protection. The aphids
also produce a white powder which covers their
bodies. Nymphs are smaller than adults, pale and
initially not so globular. Honeydew (sticky sugary
secretion) is produced. Sooty mould grows on it
and the white woolly threads stick to it.
Above ground limbs & lateral growth.
Woolly aphids feed on the laterals and trunks of
apple trees by piercing and sucking plant sap.
However, they can only attack wood where the
bark is still thin, eg lateral growth, or where the
bark has been broken as a result of injury or at
existing feeding sites. The feeding sites become
gnarled and lumpy and trees may be weakened.
Lateral growth may become cracked and distorted
and most or all the buds are destroyed. Heavily
infested trees become ‘staggy’ in appearance, with
the quantity of productive wood greatly reduced.
The woolly threads secreted by the aphids
disfigure the laterals.
Fruit. Black sooty mould grows on honeydew
and the white woolly threads stick to it. Heavy
infestations:
Disfigure fruit.
Annoy pickers.
Cause fruit to fall prematurely.
Interfere with the coloring of red varieties.
Downgrade commercial fruit.
Roots. Heavy infestations, mostly on roots near
the surface, produce characteristic lumpy swellings
and can severely stunt growth, particularly in
young trees. But once trees are established, root
infestations do not usually affect their vigour.
General. The major cause of damage occurs
when large aphid populations build up on laterals.
The copious amounts of honeydew encourages
sooty mould which interferes with the tree's growth
by preventing photosynthesis.
Diagnostics.
White woolly threads, black aphids, sticky
honeydew.
Black sooty mould growing on the honeydew.
Limited host range.
Do not confuse with mealybugs.
Do not confuse with powdery mildew, etc.
Gnarled and lumpy lateral growth.
Fig. 107. Woolly aphid (Eriosoma lanigerum).
Top left: Swellings on lateral growth caused by
aphids feeding. Lower left: Galls on apple root.
PhotoNSW Dept of Industry and Investment. Right: Twigs with
aphids under woolly threads. PhotoCIT, Canberra (P.W.Unger).
Insects and allied pests - Hemiptera (bugs, aphids, etc) 155