Agriculture Reference
In-Depth Information
root surface. These lesions can completely encircle the root.
Reniform nematodes reduce the number of lateral and fine
feeder roots; the remainder elongate normally so that
plants retain good soil anchorage. Root-knot nematodes
cause stunting, yellowing and dieback of plants.
preparation will directly reduce nematode numbers;
it will allow the soil to dry out and accelerate the
breakdown of plant material that harbours nematodes.
Use preplant soil sampling to assess the level of
nematodes. If signifi cant numbers are found, apply
a registered nematicide before planting.
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Importance
Root-knot nematodes are the most damaging of all
nematodes in Queensland pineapple fields. Fruit yields can
be markedly reduced, particularly in ratoon crops. Root
lesion is common in all pineapple-growing districts and
high populations can reduce ratoon crop yields, but effects
are often masked by symptoms caused by root-knot
nematodes. Reniform nematode is largely restricted to
north Queensland, where it can cause major losses.
In the plant crop, use nematode testing to determine
nematode levels at six to eight months, and at 12 months,
after planting. If signifi cant numbers are found, apply a
registered nematicide.
•
Use nematode testing to assess the incidence of
nematodes immediately after plant crop harvest and
apply a registered nematicide if testing indicates the need
for treatment.
•
Life cycle
Juvenile root-knot nematodes invade roots near the tips. As
these mature into females, the cells enlarge and develop
into galls. When each female matures, it will lay some
2000 eggs in a small mass on the root surface. Between
25 and 30 days after the initial egg laying, juveniles invade
the root. Root-knot nematodes produce many generations
each year and soil populations can increase rapidly in
optimal growing conditions.
VIRUSES
MEALYBUG WILT DISEASE
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Cause
Latest evidence suggests that mealybug wilt disease is
caused by an ampelovirus(-es) transmitted by mealybugs.
Root-lesion nematodes primarily live in the plant roots. They
only enter the soil when migrating from one plant to the
other. They move through the root cells, feeding on the cells
and generally disrupting the physiological processes of the
root. This nematode first moults inside the egg then passes
through three juvenile stages before reaching adulthood.
Both juvenile and adult nematodes can penetrate roots, so
that infested roots contain all development stages: eggs,
juveniles and adults. Reproduction occurs quickly in
summer and each generation is completed in 29 to 45 days.
Reniform nematodes are well adapted to warm dry
conditions, and very high populations can develop very
quickly. They have a wide host range, including cow peas
and watermelons, which may be grown in rotation with
pineapple. Unlike root-knot nematode, the reniform
nematode does not have to feed when it hatches and can
survive in fallow soil for long periods.
Management
•
Most nematode populations, except for reniform
nematodes, decline rapidly in a weed-free or host-free
fallow period. However, more than six months' fallow is
needed for good results. For short fallows, keep the fi elds
free from weeds. For longer fallows, plant inter-fallow
crops that are not hosts for nematodes. Thorough land
Fig 16.27 Mealy bug wilt symptoms on pineapple leaves. This disease
causes reddening and yellowing in leaves and dieback in the leaf tips.
