Agriculture Reference
In-Depth Information
(b)
(a)
Figure 18.27
(a) Woodlouse, can be a pest in greenhouses; (b) Geophilus centipede, a useful predator on soil
pests
caused by these tiny animals are sometimes confused
with those caused by fungi or bacteria
.
One horticulturally damaging species is described
below. Four others are mentioned.
Potato cyst nematode (
Globodera
rostochiensis and G. pallida
)
Damage
. This serious pest is found in most soils
that have grown potatoes. Leaves become yellow
and plants become stunted (Figure 18.28) and
occasionally killed. The distribution of damage in the
plot is characteristically in patches. Tomatoes grown in
greenhouses and outdoors may be similarly affected.
The pest may be diagnosed in the field by the tiny,
mature white or yellow, onion-shaped females (
cysts
)
that are
attached to
the potato roots (a hand-lens is
needed for this observation).
Life cycle
. A proportion of the eggs in the soil hatch
in spring, stimulated by chemicals that are produced
by neighbouring potato roots. The larvae invade the
roots, disturbing
translocation
in xylem and phloem
tissues, and sucking up plant cell contents. When the
adult male and female nematodes are fully developed,
they wriggle to the outside of the root, and the now
swollen female leaves only her head inserted in the
plant tissues (Figure 18.29). After fertilization, the
white female swells and becomes almost spherical,
about 0.5 mm in size, and contains 200-600 eggs. As
the potato crop reaches harvest, the female changes
colour. In
G. rostochiensis
(the golden nematode),
the change is from white to
yellow
and then to dark
18
Figure 18.28
Potatoes stunted by potato cyst
nematode
