Agriculture Reference
In-Depth Information
(b)
(a)
Figure 18.25 (a) Fine mottling symptoms caused by two-
spotted mite on a palm leaf; (b) fi ne strands ('webbing')
produced by the mites; (c) two-spotted mite being attacked
by Phytoseiulus predator
(c)
Life cycle . This pest thrives best in high greenhouse
temperatures. It lives mainly on the under-surface of
leaves. It is 1 mm long, is yellowish in colour, with two
black spots (Figure 18.25a) but become red in autumn
The female lays about 100 tiny spherical eggs on
the underside of the leaf. The life-cycle length varies
markedly from 62 days at 10°C to six days at 35°C,
when the pest's multiplication potential is extremely
high. In autumn, the female (with eggs inside her)
hibernates (diapauses). She often emerges in March
or April. A second species ( Tetranychus cinnabarinus )
is orange-red in colour all year and does not hibernate.
Spread . This occurs when adults and nymphs crawl
from plant to plant. This pest is often carried into
greenhouses on pot plants, unnoticed because of its
small size.
Control . This may be achieved in several ways.
Gardeners should carefully check incoming plants
for the presence of the mite, using a hand-lens if
necessary. A predatory mite, Phytoseiulus persimilis,
is available from specialist biological control
companies and is introduced into cucumber and other
greenhouse plants (see also p. 195 for more details).
There are spray products containing fatty acids or
plant extracts that control the mite on edible and
non-edible plants. Abamectin is used on non-edible
crops.
18
Gall mite of blackcurrant
( Cecidophyopsis ribis )
This tiny mite lives inside the blackcurrant bud
(Figure 18.26) causing distorted leaf and flower
development, and carries blackcurrant reversion
disease. 'Ben Hope' blackcurrant cultivar is resistant
to the pest. Disease-free bushes should be planted.
Pruning out infected stems is useful. A spray of
colloidal sulphur in May and June reduces the
dispersal of the mites as they emerge from infected
buds.
Tarsonemid mite ( Tarsonemus pallidus )
This mite causes distortion of developing leaves and
flowers (resulting from the pest's injected toxins).
These are the main symptom of this pest, particularly
 
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