PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
‘Overwintering’
In cold areas, most males die as the temperature
drops. A few survive and these, with mature
females, change colour to bright red (‘red
spider’) and hibernate.
On deciduous plants, eg roses and apples, mites
descend from plants and ‘camp’ on the lower
parts of the main stem, in cracks or damaged
bark and under debris at the base of main stems.
Some mites migrate to nearby perennial weeds
where they may feed and reproduce at a very
slow rate during winter.
On evergreen hosts, eg violets, females also
change colour but often remain on the plants,
feeding and reproducing at a very slow rate.
In greenhouses, mites continually reproduce.
Spread
By crawling from plant to plant.
On windblown leaves, clothing, plant debris,
visiting insects.
By movement of infested leafy plants in pots.
Between nurseries on plants. Cuttings.
By propagation from infected plants (with
leaves).
Conditions favoring
High temperatures during dry or humid
conditions. Outdoors most damage is caused
during the warmer summer months. Bodman et
al (1996) calculated the time required for a
population to double at particular temperature:
13 days 16.5 o C
7 days 21 o C
4 days 25.5 o C (optimum temperature)
3 days 29.5 o C
Heavy falls of rain or good irrigation can
reduce the effects of infestation.
Broad spectrum miticides and insecticides
which eliminate naturally occurring predators, eg
when carbaryl is used extensively on apples to
control other pests, populations of the twospotted
mite's natural enemies are reduced or killed off.
Synthetic pyrethroids may also cause upsurges
of mites due to adverse effects on beneficials.
Application of fruit fly baits too high in the
tree disrupts predatory mites causing outbreaks
of twospotted mites especially in Meyer lemons.
Water-stressed plants.
House plants are susceptible during winter
months especially if artificial heating is used.
Development of resistant mite populations
due to continued use of one miticide.
Tiny black mite-eating ladybird
(Stethorus spp.) about 2mm long, often
found on the back of mite-infested rose
leaves.
Predatory mite
Predatory mites, 0.7mm
long and pear-shaped; Top and
Right: Twospotted mites.
Fig. 126. A spider mite
(Tetranychus sp.). Probably
bean spider mite, adults
of which are red and do not
have 2 distinctive markings
on either side of their body.
PhotoNSW Dept of Industry and
Investment (E.H.Zeck).
All magnified about x30
1. Underside of leaf showing
eggs
2. 6-legged larvae and
8-legged nymphs
3. Adult mites
Actual size
4. Bean plants injured
by spider mites (0.5 mm long)
Insects and allied pests - Mites (Arachnida, Acarina) 203