PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
DISTRIBUTION
WITHIN PLANTS
Female nematodes
on gall
Foliar nematode
damage
In terms of habitat, plant parasitic nematodes are either endoparasitic or
ectoparasitic.
ENDOPARASITIC NEMATODES
Species that enter the host and feed from within the host.
Sedentary. Species which do not move around extensively once inside the plant,
eg root knot nematodes.
Migratory. Species which do move around extensively inside the plant, eg foliar
nematodes and stem and bulb nematode, root lesion and citrus nematodes.
ECTOPARASITIC NEMATODES
Species that do not normally penetrate root tissue but feed only on the cells near the
surface.
Sedentary. Species do not move around on the outside of the plant, they find a
place to feed and stay there, eg ring nematode.
Migratory. Species feed on the cells on the root surface but do not become
attached and move around from place to place, eg dagger nematode.
EGG HATCHING
Most nematode eggs hatch freely in water.
However, the eggs of some species are stimulated to hatch by substances produced
by the roots of the surrounding host plant, which diffuses into the surrounding soil.
OBLIGATE PARASITES
Plant parasitic nematodes are obligate parasites - they can only complete their
life cycles on living plants. This can be a weakness and exploited in control.
DISEASE
CYCLE
Host
Host, host debris
Host, host debris, soil
Although all plant parasitic nematodes are obligate parasites and so
only attack and complete their life cycle on living plants, many stages of their life
cycle may be found in soil, plant debris, corms, tubers, bulbs, seed, etc.
HOST ONLY
In some plant parasitic species, all stages (eggs, larvae and adults) may be found in
or on the host plant, while in other species only one or two stages may be found
in or on the host plant.
Depending on the species, various stages (eggs, larvae and adults) may be found in
or on roots, stems, leaves, seed, corms and other plant parts.
HOST AND HOST DEBRIS
Plant debris from infected plants may carry various stages of nematodes (eggs,
larvae and adults).
HOST, HOST DEBRIS AND SOIL
Most plant parasitic nematodes live part of their lives in soil.
Large numbers are usually also found around the roots of host plants so that the
depth at which nematodes can be found and should be sampled, will depend on the
type of crop being grown, previous crops, soil type and the method of growing the
crop.
In vegetables crops nematodes will be concentrated in the surface layers, eg
20-30 cm for carrot crops, while in other crops nematodes may be found as deep as
150 cm.
Seek advice on the depth and methods of sampling soil for nematode
testing for your crop.
Nematode diseases 259